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  • 1.
    Abudayyeh, H.A.
    et al.
    Department of Physics, Al-Quds University, Jerusalem.
    Barghouthi, I.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Centrifugal acceleration at high altitudes above the polar cap: A Monte Carlo simulation2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 8, p. 6409-6426Article in journal (Refereed)
    Abstract [en]

    A Monte Carlo simulation was used to study the outflow of O+ and H+ ions along three flight trajectories above the polar cap up to altitudes of about 15 RE. Barghouthi (2008) developed a model on the basis of altitude and velocity-dependent wave-particle interactions and a radial geomagnetic field which includes the effects of ambipolar electric field and gravitational and mirror forces. In the present work we improve this model to include the effect of the centrifugal force, with the use of relevant boundary conditions. In addition, the magnetic field and flight trajectories, namely, the central polar cap (CPC), nightside polar cap (NPC), and cusp, were calculated using the Tsyganenko T96 model. To simulate wave-particle interactions, the perpendicular velocity diffusion coefficients for O+ ions in each region were determined such that the simulation results fit the observations. For H+ ions, a constant perpendicular velocity diffusion coefficient was assumed for all altitudes in all regions as recommended by Nilsson et al. (2013). The effect of centrifugal acceleration was simulated by considering three values for the ionospheric electric field: 0 (no centrifugal acceleration), 50, and 100 mV/m. It was found that the centrifugal acceleration increases the parallel bulk velocity and decreases the parallel and perpendicular temperatures of both ion species at altitudes above about 4 RE. Centrifugal acceleration also increases the temperature anisotropy at high altitudes. At a given altitude, centrifugal acceleration decreases the density of H+ ions while it increases the density of O+ ions. This implies that with higher centrifugal acceleration more O+ ions overcome the potential barrier. It was also found that aside from two exceptions centrifugal acceleration has the same effect on the velocities of both ions. This implies that the centrifugal acceleration is universal for all particles. The parallel bulk velocities at a given value of ionospheric electric field were highest in the cusp followed by the CPC followed by the NPC. In this study a region of no wave-particle interaction was assumed in the CPC and NPC between 3.7 and 7.5 RE. In this region the perpendicular temperature was found to decrease with altitude due to perpendicular adiabatic cooling.

  • 2. Adriani, O.
    et al.
    Barbarino, G. C.
    Bazilevskaya, G. A.
    Bellotti, R.
    Boezio, M.
    Bogomolov, E. A.
    Bongi, M.
    Bonvicini, V.
    Bottai, S.
    Bruno, A.
    Cafagna, F.
    Campana, D.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Casolino, M.
    Castellini, G.
    De Donato, C.
    De Santis, C.
    De Simone, N.
    Di Felice, V.
    Formato, V.
    Galper, A. M.
    Karelin, A. V.
    Koldashov, S. V.
    Koldobskiy, S.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A.
    Malakhov, V.
    Marcelli, L.
    Martucci, M.
    Mayorov, A. G.
    Menn, W.
    Merge, M.
    Mikhailov, V. V.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Munini, R.
    Osteria, G.
    Palma, F.
    Panico, B.
    Papini, P.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Picozza, P.
    Ricci, M.
    Ricciarini, S. B.
    Sarkar, R.
    Scotti, V.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G. I.
    Voronov, S. A.
    Yurkin, Y. T.
    Zampa, G.
    Zampa, N.
    Reentrant albedo proton fluxes measured by the PAMELA experiment2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 5, p. 3728-3738Article in journal (Refereed)
    Abstract [en]

    We present a precise measurement of downward going albedo proton fluxes for kinetic energy above similar to 70 MeV performed by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment at an altitude between 350 and 610 km. On the basis of a trajectory tracing simulation, the analyzed protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and untrapped spreading over all latitudes, including both short-lived (precipitating) and long-lived (pseudotrapped) components. In addition, features of the penumbra region around the geomagnetic cutoff were investigated in detail. PAMELA results significantly improve the characterization of the high-energy albedo proton populations at low-Earth orbits.

  • 3.
    Aikio, A. T.
    et al.
    Univ Oulu, Ionospher Phys Unit, Oulu, Finland.
    Vanhamaeki, H.
    Kyushu Univ, Int Ctr Space Weather Sci & Educ, Fukuoka, Japan;Univ Oulu, Ionospher Phys Unit, Oulu, Finland.
    Workayehu, A. B.
    Univ Oulu, Ionospher Phys Unit, Oulu, Finland.
    Virtanen, I. I.
    Univ Oulu, Ionospher Phys Unit, Oulu, Finland.
    Kauristie, K.
    Finnish Meteorol Inst, Helsinki, Finland.
    Juusola, L.
    Finnish Meteorol Inst, Helsinki, Finland.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Knudsen, D.
    Univ Calgary, Dept Phys & Astron, Calgary, AB, Canada.
    Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 6, p. 5140-5158Article in journal (Refereed)
    Abstract [en]

    We present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5 degrees wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F-region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10 degrees in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13-kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near-Earth magnetotail.

  • 4.
    Ala-Lahti, Matti
    et al.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Kilpua, Emilia K. J.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Soucek, Jan
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic.
    Pulkkinen, Tuija, I
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA;Aalto Univ, Sch Elect Engn, Espoo, Finland.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Alfven Ion Cyclotron Waves in Sheath Regions Driven by Interplanetary Coronal Mass Ejections2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 3893-3909Article in journal (Refereed)
    Abstract [en]

    We report on a statistical analysis of the occurrence and properties of Alfven ion cyclotron (AIC) waves in sheath regions driven by interplanetary coronal mass ejections (ICMEs). We have developed an automated algorithm to identify AIC wave events from magnetic field data and apply it to investigate 91 ICME sheath regions recorded by the Wind spacecraft. Our analysis focuses on waves generated by the ion cyclotron instability. AIC waves are observed to be frequent structures in ICME-driven sheaths, and their occurrence is the highest in the vicinity of the shock. Together with previous studies, our results imply that the shock compression has a crucial role in generating wave activity in ICME sheaths. AIC waves tend to have their frequency below the ion cyclotron frequency, and, in general, occur in plasma that is stable with respect to the ion cyclotron instability and has lower ion beta(parallel to) than mirror modes. The results suggest that the ion beta anisotropy beta(perpendicular to)/beta(parallel to) > 1 appearing in ICME sheaths is regulated by both ion cyclotron and mirror instabilities.

  • 5.
    Allen, R. C.
    et al.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Zhang, J. -C
    Kistler, L. M.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Spence, H. E.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Lin, R. -L
    Klecker, B.
    Max Planck Inst Extraterr Phys, D-85748 Garching, Germany..
    Dunlop, M. W.
    Rutherford Appleton Lab, Div Space Sci, Harwell, Oxon, England..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Jordanova, V. K.
    Los Alamos Natl Lab, Los Alamos, NM USA..
    A statistical study of EMIC waves observed by Cluster: 1. Wave properties2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 7, p. 5574-5592Article in journal (Refereed)
    Abstract [en]

    Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10years (2001-2010) of data from Cluster, totaling 25,431min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.

  • 6.
    Allen, R. C.
    et al.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Zhang, J. -C
    Kistler, L. M.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Spence, H. E.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Lin, R. -L
    Klecker, B.
    Max Planck Inst Extraterr Phys, Garching, Germany..
    Dunlop, M. W.
    Rutherford Appleton Lab, SSTD, Div Space Sci, Didcot, Oxon, England..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Jordanova, V. K.
    Los Alamos Natl Lab, Los Alamos, NM USA..
    A statistical study of EMIC waves observed by Cluster: 2. Associated plasma conditions2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 7, p. 6458-6479Article in journal (Refereed)
    Abstract [en]

    This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10years (2001-2010) of Cluster observations. In the first paper, an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)-distance as well as magnetic local time (MLT)-L frames. This paper focuses on the distribution of EMIC wave-associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H+ anisotropy, electron and hot H+ density measurements, hot H+ parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well-known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off-equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere.

  • 7. Alm, L.
    et al.
    Argall, M. R.
    Torbert, R. B.
    Farrugia, C. J.
    Burch, J. L.
    Ergun, R. E.
    Russell, C. T.
    Strangeway, R. J.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Giles, B. L.
    Shuster, J.
    EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 3, p. 3262-3276Article in journal (Refereed)
    Abstract [en]

    We present a method for mapping the position of satellites relative to the X line using the measured B-L and B-N components of the magnetic field and apply it to the Magnetospheric multiscale (MMS) encounter with the electron diffusion region (EDR) which occurred on 13:07 UT on 16 October 2015. Mapping the data to our parametric space succeeds in capturing many of the signatures associated with magnetic reconnection and the electron diffusion region. This offers a method for determining where in the reconnection region the satellites were located. In addition, parametric mapping can also be used to present data from numerical simulations. This facilitates comparing data from simulations with data from in situ observations as one can avoid the complicated process using boundary motion analysis to determine the geometry of the reconnection region. In parametric space we can identify the EDR based on the collocation of several reconnection signatures, such as electron nongyrotropy, electron demagnetization, parallel electric fields, and energy dissipation. The EDR extends 2-3km in the normal direction and in excess of 20km in the tangential direction. It is clear that the EDR occurs on the magnetospheric side of the topological X line, which is expected in asymmetric reconnection. Furthermore, we can observe a north-south asymmetry, where the EDR occurs north of the peak in out-of-plane current, which may be due to the small but finite guide field.

  • 8.
    Alm, L.
    et al.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Argall, M. R.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA.;Southwest Res Inst, San Antonio, TX USA..
    Farrugia, C. J.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Russell, C. T.
    Univ Calif Los Angeles, IGPP EPSS, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, IGPP EPSS, Los Angeles, CA USA..
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Stockholm, Sweden..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Shuster, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Coll Comp Math & Nat Sci, College Pk, MD 20742 USA..
    EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 3, p. 3262-3276Article in journal (Refereed)
    Abstract [en]

    We present a method for mapping the position of satellites relative to the X line using the measured B-L and B-N components of the magnetic field and apply it to the Magnetospheric multiscale (MMS) encounter with the electron diffusion region (EDR) which occurred on 13:07 UT on 16 October 2015. Mapping the data to our parametric space succeeds in capturing many of the signatures associated with magnetic reconnection and the electron diffusion region. This offers a method for determining where in the reconnection region the satellites were located. In addition, parametric mapping can also be used to present data from numerical simulations. This facilitates comparing data from simulations with data from in situ observations as one can avoid the complicated process using boundary motion analysis to determine the geometry of the reconnection region. In parametric space we can identify the EDR based on the collocation of several reconnection signatures, such as electron nongyrotropy, electron demagnetization, parallel electric fields, and energy dissipation. The EDR extends 2-3km in the normal direction and in excess of 20km in the tangential direction. It is clear that the EDR occurs on the magnetospheric side of the topological X line, which is expected in asymmetric reconnection. Furthermore, we can observe a north-south asymmetry, where the EDR occurs north of the peak in out-of-plane current, which may be due to the small but finite guide field.

  • 9. Alm, L.
    et al.
    Farrugia, C. J.
    Paulson, K. W.
    Argall, M. R.
    Torbert, R. B.
    Burch, J. L.
    Ergun, R. E.
    Russell, C. T.
    Strangeway, R. J.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Giles, B. L.
    Differing Properties of Two Ion-Scale Magnetopause Flux Ropes2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 114-131Article in journal (Refereed)
    Abstract [en]

    In this paper, we present results from the Magnetospheric Multiscale constellation encountering two ion-scale, magnetopause flux ropes. The two flux ropes exhibit very different properties and internal structure. In the first flux rope, there are large differences in the currents observed by different satellites, indicating variations occurring over sub-d(i) spatial scales, and time scales on the order of the ion gyroperiod. In addition, there is intense wave activity and particle energization. The interface between the two flux ropes exhibits oblique whistler wave activity. In contrast, the second flux rope is mostly quiescent, exhibiting little activity throughout the encounter. Changes in the magnetic topology and field line connectivity suggest that we are observing flux rope coalescence.

  • 10.
    Alm, L.
    et al.
    Univ New Hampshire, Space Sci Ctr, Durham, NH, USA.
    Farrugia, C. J.
    Univ New Hampshire, Space Sci Ctr, Durham, NH USA.
    Paulson, K. W.
    Univ New Hampshire, Space Sci Ctr, Durham, NH USA.
    Argall, M. R.
    Univ New Hampshire, Space Sci Ctr, Durham, NH USA.
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH USA; Southwest Res Inst, San Antonio, TX USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA.
    Russell, C. T.
    Univ Calif Los Angeles, IGPP EPSS, Los Angeles, CA USA.
    Strangeway, R. J.
    Univ Calif Los Angeles, IGPP EPSS, Los Angeles, CA USA.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    KTH Royal Inst Technol, Dept Space & Plasma Phys, Stockholm, Sweden.
    Marklund, G. T.
    KTH Royal Inst Technol, Dept Space & Plasma Phys, Stockholm, Sweden.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Differing Properties of Two Ion-Scale Magnetopause Flux Ropes2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 114-131Article in journal (Refereed)
    Abstract [en]

    In this paper, we present results from the Magnetospheric Multiscale constellation encountering two ion‐scale, magnetopause flux ropes. The two flux ropes exhibit very different properties and internal structure. In the first flux rope, there are large differences in the currents observed by different satellites, indicating variations occurring over sub‐di spatial scales, and time scales on the order of the ion gyroperiod. In addition, there is intense wave activity and particle energization. The interface between the two flux ropes exhibits oblique whistler wave activity. In contrast, the second flux rope is mostly quiescent, exhibiting little activity throughout the encounter. Changes in the magnetic topology and field line connectivity suggest that we are observing flux rope coalescence.

  • 11.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Li, Bin
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistical altitude distribution of the auroral density cavity2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 996-1006Article in journal (Refereed)
    Abstract [en]

    The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

  • 12.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    In situ observations of density cavities extending above the auroral acceleration region2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 7, p. 5286-5294Article in journal (Refereed)
    Abstract [en]

    The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

  • 13.
    Andrews, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gurnett, D. A.
    Morgan, D.
    Nemec, F.
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Control of the topside Martian ionosphere by crustal magnetic fields2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 3042-3058Article in journal (Refereed)
    Abstract [en]

    We present observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument onboard Mars Express of the thermal electron plasma density of the Martian ionosphere and investigate the extent to which it is influenced by the presence of Mars's remnant crustal magnetic fields. We use locally measured electron densities, derived when MARSIS is operating in active ionospheric sounding (AIS) mode, covering an altitude range from approximate to 300km to approximate to 1200km. We compare these measured densities to an empirical model of the dayside ionospheric plasma density in this diffusive transport-dominated regime. We show that small spatial-scale departures from the averaged values are strongly correlated with the pattern of the crustal fields. Persistently elevated densities are seen in regions of relatively stronger crustal fields across the whole altitude range. Comparing these results with measurements of the (scalar) magnetic field also obtained by MARSIS/AIS, we characterize the dayside strength of the draped magnetic fields in the same regions. Finally, we provide a revised empirical model of the plasma density in the Martian ionosphere, including parameterizations for both the crustal field-dominated and draping-dominated regimes.

  • 14.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Barabash, S.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Hall, B. E. S.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Holmström, M.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Lester, M.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Morgan, D. D.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ramstad, R.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Sanchez-Cano, B.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Way, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. NASA Goddard Inst Space Studies, New York, NY USA..
    Witasse, O.
    ESA ESTEC, Noordwijjk, Netherlands..
    Plasma observations during the Mars atmospheric "plume" event of March-April 20122016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 4, p. 3139-3154Article in journal (Refereed)
    Abstract [en]

    We present initial analyses and conclusions from plasma observations made during the reported "Mars plume event" of March-April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator, the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.

  • 15.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Leyser, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morgan, D. D.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA USA.
    Kopf, A. J.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA USA.
    Fallows, K.
    Boston Univ, Ctr Space Phys, Boston, MA USA.
    Withers, P.
    Boston Univ, Ctr Space Phys, Boston, MA USA; Boston Univ, Dept Astron, Commonwealth Ave, Boston, MA USA.
    MARSIS Observations of Field-Aligned Irregularities and Ducted Radio Propagation in the Martian Ionosphere2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 8, p. 6251-6263Article in journal (Refereed)
    Abstract [en]

    Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp-like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere.

  • 16.
    Andriopoulou, Maria
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nakamura, Rumi
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Wellenzohn, Simon
    Karl Franzens Univ Graz, Inst Geophys Astrophys & Meteorol, Graz, Austria..
    Torkar, Klaus
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys IRF, Uppsala, Sweden..
    Dorelli, John
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2620-2629Article in journal (Refereed)
    Abstract [en]

    Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.

  • 17.
    Andriopoulou, Maria
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Nakamura, Rumi
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Wellenzohn, Simon
    Karl Franzens Univ Graz, Inst Geophys Astrophys & Meteorol, Graz, Austria.
    Torkar, Klaus
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.
    Lindqvist, Per-Arne
    KTH Royal Inst Technol, Dept Space & Plasma Phys, Stockholm, Sweden.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dorelli, John
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA.
    Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2620-2629Article in journal (Refereed)
    Abstract [en]

    Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.

  • 18.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Li, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Outflow of low-energy ions and the solar cycle2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 1072-1085Article in journal (Refereed)
    Abstract [en]

    Magnetospheric ions with energies less than tens of eV originate from the ionosphere. Positive low-energy ions are complicated to detect onboard sunlit spacecraft at higher altitudes, which often become positively charged to several tens of volts. We use two Cluster spacecraft and study low-energy ions with a technique based on the detection of the wake behind a charged spacecraft in a supersonic ion flow. We find that low-energy ions usually dominate the density and the outward flux in the geomagnetic tail lobes during all parts of the solar cycle. The global outflow is of the order of 10(26) ions/s and often dominates over the outflow at higher energies. The outflow increases by a factor of 2 with increasing solar EUV flux during a solar cycle. This increase is mainly due to the increased density of the outflowing population, while the outflow velocity does not vary much. Thus, the outflow is limited by the available density in the ionospheric source rather than by the energy available in the magnetosphere to increase the velocity.

  • 19.
    Argall, M. R.
    et al.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Paulson, K.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Alm, L.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Rager, A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Dorelli, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Shuster, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Wang, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA; Southwest Res Inst, San Antonio, TX USA.
    Vaith, H.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Dors, I.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Chutter, M.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Farrugia, C.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA.
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA.
    Pollock, C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Gershman, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Lavraud, B.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, UPS, Toulouse, France..
    Russell, C. T.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Lindqvist, P. -A
    KTH Royal Inst Technol, Stockholm, Sweden.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ergun, R. E.
    Univ Colorado Boulder, Boulder, CO USA.
    Ahmadi, N.
    Univ Colorado Boulder, Boulder, CO USA.
    Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 146-162Article in journal (Refereed)
    Abstract [en]

    Abstract: We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported approximate to 66eV agyrotropic "crescent" population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500eV is also more persistent than at 66eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500eV, but only in close proximity to the EDR at 66eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90 degrees, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma.

    Plain Language Summary: The process of reconnection involves an explosive transfer of magnetic energy into particle energy. When energetic particles contact modern technology such as satellites, cell phones, or other electronic devices, they can cause random errors and failures. Exactly how particles are energized via reconnection, however, is still unknown. Fortunately, the Magnetospheric Multiscale mission is finally able to detect and analyze reconnection processes. One recent finding is that energized particles take on a crescent-shaped configuration in the vicinity of reconnection and that this crescent shape is related to the energy conversion process. In our paper, we explain why the crescent shape has not been observed until now and inspect particle motions to determine what impact it has on energy conversion. When reconnection heats the plasma, the crescent shape forms from the cool, tenuous particles. As plasmas from different regions mix, dense, nonheated plasma obscures the crescent shape in our observations. The highest-energy particle population created by reconnection, though, also contains features of the crescent shape that are more persistent but appear less dramatically in the data.

  • 20. Argall, M. R.
    et al.
    Paulson, K.
    Alm, L.
    Rager, A.
    Dorelli, J.
    Shuster, J.
    Wang, S.
    Torbert, R. B.
    Vaith, H.
    Dors, I.
    Chutter, M.
    Farrugia, C.
    Burch, J.
    Pollock, C.
    Giles, B.
    Gershman, D.
    Lavraud, B.
    Russell, C. T.
    Strangeway, R.
    Magnes, W.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yu. V.
    Ergun, R. E.
    Ahmadi, N.
    Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 146-162Article in journal (Refereed)
    Abstract [en]

    We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported approximate to 66eV agyrotropic "crescent" population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500eV is also more persistent than at 66eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500eV, but only in close proximity to the EDR at 66eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90 degrees, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma. Plain Language Summary The process of reconnection involves an explosive transfer of magnetic energy into particle energy. When energetic particles contact modern technology such as satellites, cell phones, or other electronic devices, they can cause random errors and failures. Exactly how particles are energized via reconnection, however, is still unknown. Fortunately, the Magnetospheric Multiscale mission is finally able to detect and analyze reconnection processes. One recent finding is that energized particles take on a crescent-shaped configuration in the vicinity of reconnection and that this crescent shape is related to the energy conversion process. In our paper, we explain why the crescent shape has not been observed until now and inspect particle motions to determine what impact it has on energy conversion. When reconnection heats the plasma, the crescent shape forms from the cool, tenuous particles. As plasmas from different regions mix, dense, nonheated plasma obscures the crescent shape in our observations. The highest-energy particle population created by reconnection, though, also contains features of the crescent shape that are more persistent but appear less dramatically in the data.

  • 21. Bader, A.
    et al.
    Wieser, G. Stenberg
    Andre, M.
    Wieser, M.
    Futaana, Y.
    Persson, M.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, H.
    Zhang, T. L.
    Proton Temperature Anisotropies in the Plasma Environment of Venus2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3312-3330Article in journal (Refereed)
    Abstract [en]

    Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T-perpendicular to) and parallel (T-parallel to) to the background magnetic field. We calculate average values of T-perpendicular to and T-parallel to for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T-perpendicular to/T-parallel to > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near-subsolar magnetosheath (T-perpendicular to/ T-parallel to approximate to 3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

  • 22.
    Bader, A.
    et al.
    Swedish Inst Space Phys, Kiruna, Sweden;Lulea Tekniska Univ, Kiruna, Sweden;Univ Lancaster, Phys, Lancaster, England.
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wieser, M.
    Swedish Inst Space Phys, Kiruna, Sweden.
    Futaana, Y.
    Swedish Inst Space Phys, Kiruna, Sweden.
    Persson, M.
    Swedish Inst Space Phys, Kiruna, Sweden;Umea Univ, Dept Phys, Umea, Sweden.
    Nilsson, H.
    Swedish Inst Space Phys, Kiruna, Sweden.
    Zhang, T. L.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Proton Temperature Anisotropies in the Plasma Environment of Venus2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3312-3330Article in journal (Refereed)
    Abstract [en]

    Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T-perpendicular to) and parallel (T-parallel to) to the background magnetic field. We calculate average values of T-perpendicular to and T-parallel to for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T-perpendicular to/T-parallel to > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near-subsolar magnetosheath (T-perpendicular to/ T-parallel to approximate to 3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

  • 23.
    Bader, Alexander
    et al.
    Luleå University of Technology. Swedish Institute of Space Physics, Kiruna, Sweden. Physics, Lancaster University, Lancaster, United Kingdom.
    Stenberg Weiser, G.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    André, M.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Wieser, M.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Futaana, Y.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Persson, M.
    Swedish Institute of Space Physics, Kiruna, Sweden. Department of Physics, Umeå Universitet, Umeå, Sweden.
    Nilsson, H.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Zhang, T.L.
    Space Research Institute, Austrian Academy of Science, Graz, Austria.
    Proton Temperature Anisotropies in the Plasma Environment of Venus2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3312-3330Article in journal (Refereed)
    Abstract [en]

    Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T⊥) and parallel (T‖) to the background magnetic field. We calculate average values of T⊥ and T‖ for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T⊥/T‖ > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near‐subsolar magnetosheath (T⊥/T‖≈3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

  • 24.
    Badman, S. V.
    et al.
    JAXA Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2525210, Japan..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cowley, S. W. H.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Lamy, L.
    Observ Paris, Meudon, France..
    Provan, G.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Tao, C.
    JAXA Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2525210, Japan..
    Kasahara, S.
    JAXA Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2525210, Japan..
    Kimura, T.
    JAXA Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2525210, Japan..
    Fujimoto, M.
    JAXA Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2525210, Japan..
    Melin, H.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Stallard, T.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Brown, R. H.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ USA..
    Baines, K. H.
    Univ Wisconsin Madison, SSEC, Madison, NJ USA..
    Rotational modulation and local time dependence of Saturn's infrared H-3(+) auroral intensity2012In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 117, article id A09228Article in journal (Refereed)
    Abstract [en]

    Planetary auroral emissions reveal the configuration of magnetospheric field-aligned current systems. In this study, Cassini Visual and Infrared Mapping Spectrometer (VIMS) observations of Saturn's pre-equinox infrared H-3(+) aurorae were analysed to show (a) rotational modulation of the auroral intensity in both hemispheres and (b) a significant local time dependence of the emitted intensity. The emission intensity is modulated by the 'planetary period' rotation of auroral current systems in each hemisphere. The northern auroral intensity also displays a lesser anti-phase dependence on the southern rotating current system, indicating that part of the southern current system closes in the northern hemisphere. The southern hemisphere aurorae were most intense in the post-dawn sector, in agreement with some past measurements of auroral field-aligned currents, UV aurora and SKR emitted power. A corresponding investigation of the northern hemisphere auroral intensity reveals a broader dawn-noon enhancement, possibly due to the interaction of the southern rotating current system with that of the north. The auroral intensity was reduced around dusk and post-midnight in both hemispheres. These observations can be explained by the interaction of a rotating field-aligned current system in each hemisphere with one fixed in local time, which is related to the solar wind interaction with magnetospheric field lines.

  • 25.
    Barghouthi, Imad A.
    et al.
    Space Research Lab, Department of Physics, Al-Quds University, Jerusalem, Department of Physics, Al-Quds University, Jerusalem.
    Abudayyeh, H.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    O+ and H+ above the polar cap: Observations and semikinetic simulations2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 1, p. 459-474Article in journal (Refereed)
    Abstract [en]

    A 1-dimensional direct simulation Monte Carlo model is used to study the outflow of O+ and H+ ions from 1.2 RE to 15.2 RE along two flight trajectories originating from the polar cap, namely the central polar cap (CPC) and the cusp. To study the effect of varying geophysical conditions and to deduce the proper set of parameters. several parameters were varied and the results were compared to corresponding data from Cluster spacecraft. First, several sets of diffusion coefficients were considered based on using diffusion coefficients calculated by Barghouthi et al. [1998], Nilsson et al. [2013], and Abudayyeh et al. [2015b] for different altitude intervals. It was found that in the central polar cap using the diffusion coefficients reported by Barghouthi et al. [1998] for altitudes lower than 3.7 RE, zero diffusion coefficients between 3.7 and 7.5 RE and diffusion coefficients from Nilsson et al. [2013] for altitudes higher than 7.5 RE provide the best fit for O+ ions. For O+ ions in the cusp the best fit was obtained for using Barghouthi et al. [1998] diffusion coefficients for altitudes lower than 3.7 RE and Nilsson et al. [2013] diffusion coefficients for altitudes higher than that. The best fit for H+ ions in both regions was obtained by using the diffusion coefficients calculated by Abudayyeh et al. [2015b]. Also, it was found that along an ion's trajectory the most recent heating dominates. Second, the strength of centrifugal acceleration was varied by using three values for the ionospheric electric field namely: 0, 50, and 100 mV/m. It was found that the value of 50 mV/m provided the best fit for both ion species in both regions. Finally the lower altitude boundary conditions and the electron temperature were varied. Increasing the electron temperature and the lower altitude O+ parallel velocity were found to increase the access of O+ ions to higher altitudes and therefore increase the density at a given altitude. The variation of all other boundary conditions only affected the densities of the ions and not the other moments due to the overwhelming effect of wave particle interaction. Furthermore varying the parameters of one ion species has no effect on the other ion species. We also compared the energy gain per ion due to wave particle interaction, centrifugal acceleration, and ambipolar electric field and found that wave particle interaction is the most important mechanism, while ambipolar electric field is relatively unimportant especially at higher altitudes.

  • 26.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Wieser, Martin
    Johansson, Fredrik
    Eriksson, Anders
    The Influence of Spacecraft Charging on Low‐Energy Ion Measurements Made by RPC‐ICA on Rosetta2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 1, article id e2019JA027478Article in journal (Refereed)
    Abstract [en]

    Spacecraft charging is problematic for low‐energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC‐ICA) on board the Rosetta spacecraft is suffering from this effect. RPC‐ICA was measuring positive ions in the vicinity of comet 67P/Churyumov‐Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low‐energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles.

  • 27.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Wieser, Martin
    Johansson, Fredrik
    Eriksson, Anders
    The Influence of Varying Spacecraft Potentials and Debye Lengths on In Situ Low-Energy Ion Measurements2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402Article in journal (Refereed)
  • 28. Blagoveshchenskaya, N. F.
    et al.
    Borisova, T. D.
    Kosch, M.
    Sergienko, T.
    Brändström, U.
    Yeoman, T. K.
    Häggström, I.
    Optical and ionospheric phenomena at EISCAT under continuous X-mode HF pumping2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 12, p. 10-483Article in journal (Refereed)
    Abstract [en]

    We present experimental results from multiinstrument observations in the high-latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X-polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458–548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave. Intensities at red and green lines varied in the range 110–950 R and 50–350 R, respectively, with a ratio of green to red line of 0.35–0.5. The results of optical observations are compared with behaviors of the HF-enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small-scale field-aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X-mode radio-induced optical emissions coexisted with HF-enhanced ion and plasma lines and strong artificial field-aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two-stream instabilities were not quenched by fully established small-scale field-aligned artificial irregularities excited by an X-mode HF pump wave.

  • 29. Blöcker, A.
    et al.
    Saur, J.
    Roth, Lorenz
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Europa's plasma interaction with an inhomogeneous atmosphere: Development of Alfvén winglets within the Alfvén wings2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 10, p. 9794-9828Article in journal (Refereed)
    Abstract [en]

    We apply a three-dimensional magnetohydrodynamic (MHD) model to study the influence of inhomogeneities in Europa's atmosphere, as, for example, water vapor plumes, on Europa's plasma interaction with the Jovian magnetosphere. In our model we have included electromagnetic induction in a subsurface water ocean, collisions between ions and neutrals, plasma production and loss due to electron impact ionization, and dissociative recombination. We present a systematic study of the plasma interaction when a local inhomogeneity in the neutral density is present within a global sputtering generated atmosphere. We show that an inhomogeneity near the north or south pole affects the plasma interaction in a way that a pronounced north-south asymmetry is generated. We find that an Alfvén winglet develops within Europa's main Alfvén wing on that side where the inhomogeneity is located. In addition to the MHD model we apply an analytic model based on the model of Saur et al. (2007) to understand the role of steep gradients and discontinuities in the interaction. We compare our model results with the measured magnetic field data from three flybys of the Galileo spacecraft at Europa which included Alfvén wing crossings. Our analysis suggests that the magnetic field might be influenced by atmospheric inhomogeneities during the E26 flyby. The findings of this work will aid in the search for plumes at Europa in future plasma and field observations.

  • 30.
    Blöcker, Aljona
    et al.
    KTH, School of Electrical Engineering (EES). Univ Cologne, Inst Geophys & Meteorol, Cologne, Germany.
    Saur, Joachim
    Univ Cologne, Inst Geophys & Meteorol, Cologne, Germany..
    Roth, Lorenz
    KTH, School of Electrical Engineering (EES).
    Strobel, Darrell F.
    Johns Hopkins Univ, Dept Earth & Planetary Sci, Baltimore, MD 21218 USA.;Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA..
    MHD Modeling of the Plasma Interaction With Io's Asymmetric Atmosphere2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 11, p. 9286-9311Article in journal (Refereed)
    Abstract [en]

    Io's atmosphere, with an average equatorial column density of >= 10(20) m(-2), exhibits significant density variations with latitude and longitude. We apply a 3-D magnetohydrodynamic model to investigate the effects of atmospheric asymmetries, both locally from volcanic plumes and globally, on the plasma and magnetic field environment of Io. The model takes into account collisions between ions and neutrals, plasma production and loss due to electron impact ionization and dissociative recombination, and the ionospheric Hall effect. Our simulation results show that volcanic plumes influence the plasma interaction locally, generating Alfven winglets within Io's global Alfven wing. Signals from individual plumes can however barely be probed by magnetic field measurements during spacecraft flybys at Io. In contrast, the surface number density, scale height, the longitudinal and latitudinal variations of the global atmosphere are crucial factors for modeling and understanding magnetic field and plasma perturbations. Comparing our model results with the magnetic field data from the 124 and 127 flybys of the Galileo spacecraft, we find that the measured perturbations can be primarily caused by the plasma interaction with the longitudinally asymmetric atmosphere. This implies that a significant magnetic induction signal from a partially molten magma ocean is not necessarily required to explain the Galileo magnetometer data.

  • 31. Borries, Claudia
    et al.
    Mahrous, Ayman M.
    Ellahouny, Nada M.
    Badeke, Ronny
    Multiple ionospheric perturbations during the Saint Patrick’s Day storm 2015 in the European-African sector2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 11, p. 11-333Article in journal (Refereed)
    Abstract [en]

    Strong ionospheric perturbations were generated by the intense geomagnetic storm on 17 March 2015. In this article, we are studying perturbations in the European-African sector observed in the total electron content (TEC). Focal points are wavelike phenomena considered as large-scale traveling ionospheric disturbances (LSTIDs). In the European-African sector, the storm produced three different types of LSTIDs: (1) a concurrent TEC perturbation at all latitudes simultaneously; (2) one LSTID propagating toward the equator, having very large wave parameters (wavelength: ≈3600 km, period: ≈120 min, and speed: ≈500 m/s); and (3) several LSTIDs propagating toward the equator with typical wave parameters (wavelength: ≈2100 km, period: ≈60 min, and speed ≈600 m/s). The third type of LSTIDs is considered to be exited as most LSTIDs either due to variations in the Joule heating or variations in the Lorentz force, whereas the first two perturbation types are rather unusual in their appearance. They occurred during the partial recovery phase when the geomagnetic perturbations were minor and the interplanetary magnetic field turned northward. A westward prompt penetration electric field is considered to excite the first perturbation signature, which indicates a sudden TEC depletion. For the second LSTID type, variations in the Lorentz force because of perturbed electric fields and a minor particle precipitation effect are extracted as possible excitation mechanisms.

  • 32. Breuillard, H.
    et al.
    Le Contel, O.
    Chust, T.
    Berthomier, M.
    Retino, A.
    Turner, D. L.
    Nakamura, R.
    Baumjohann, W.
    Cozzani, G.
    Catapano, F.
    Alexandrova, A.
    Mirioni, L.
    Graham, D. B.
    Argall, M. R.
    Fischer, D.
    Wilder, F. D.
    Gershman, D. J.
    Varsani, A.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yu. V.
    Marklund, G.
    Ergun, R. E.
    Goodrich, K. A.
    Ahmadi, N.
    Burch, J. L.
    Torbert, R. B.
    Needell, G.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Wei, H.
    Plaschke, F.
    Anderson, B. J.
    Le, G.
    Moore, T. E.
    Giles, B. L.
    Paterson, W. R.
    Pollock, C. J.
    Dorelli, J. C.
    Avanov, L. A.
    Saito, Y.
    Lavraud, B.
    Fuselier, S. A.
    Mauk, B. H.
    Cohen, I. J.
    Fennell, J. F.
    The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 93-103Article in journal (Refereed)
    Abstract [en]

    Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency similar to 100Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2f(ce) by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.

  • 33.
    Breuillard, H.
    et al.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Chust, T.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Berthomier, M.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Retino, A.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Turner, D. L.
    Aerosp Corp, Space Sci Dept, El Segundo, CA 90245 USA..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Cozzani, G.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Catapano, F.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Alexandrova, A.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Mirioni, L.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Argall, M. R.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Fischer, D.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Varsani, A.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Lindqvist, P. -A
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Marklund, G.
    Royal Inst Technol, Stockholm, Sweden..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Goodrich, K. A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Needell, G.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Chutter, M.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Rau, D.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Dors, I.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Strangeway, R. J.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Bromund, K. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Wei, H.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Anderson, B. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Le, G.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Moore, T. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Lavraud, B.
    Univ Paul Sabatier, CNRS UMR5277, Inst Rech Astrophys & Planetol, Toulouse, France..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX USA..
    Mauk, B. H.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Cohen, I. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Fennell, J. F.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, UMR7648,CNRS,Ecole Polytech,Observ Paris, Paris, France..
    The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 93-103Article in journal (Refereed)
    Abstract [en]

    Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi‐perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency ∼100 Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi‐perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05–0.2fce by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first‐time 3‐D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi‐linear pitch angle diffusion and possible signatures of nonlinear interaction with high‐amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.

  • 34.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX, USA.
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA.
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX, USA; Univ New Hampshire, Dept Phys, Durham, NH, USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX, USA.
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA; Catholic Univ Amer, Dept Phys, Washington DC, USA..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA, USA.
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Chen, L. -J
    Univ Maryland, Dept Astron, College Pk, MD, USA.
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD, USA.
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, CNRS, Ecole Polytech,Observ Paris, Paris, France.
    Russell, C. T.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA, USA.
    Strangeway, R. J.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA, USA.
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO, USA.
    Jaynes, A. N.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA, USA.
    Lindqvist, P. -A
    Royal Inst Technol, Stockholm, Sweden.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO, USA.
    Hwang, K. -J
    Southwest Res Inst, San Antonio, TX, USA.
    Goldstein, J.
    Southwest Res Inst, San Antonio, TX, USA.
    Wave Phenomena and Beam-Plasma Interactions at the Magnetopause Reconnection Region2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 2, p. 1118-1133Article in journal (Refereed)
    Abstract [en]

    This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher-frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The diffusion region is bounded by crescent-shaped electron distributions and associated dissipation just upstream of the X-line and by magnetic field-aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X-line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X-line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising-tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.

  • 35.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Chen, L. -J
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Russell, C. T.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Jaynes, A. N.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Hwang, K. -J
    Goldstein, J.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Wave Phenomena and Beam-Plasma Interactions at the Magnetopause Reconnection Region2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 2, p. 1118-1133Article in journal (Refereed)
    Abstract [en]

    This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher-frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The diffusion region is bounded by crescent-shaped electron distributions and associated dissipation just upstream of the X-line and by magnetic field-aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X-line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X-line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising-tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.

  • 36. Cai, L.
    et al.
    Oyama, S.
    Aikio, A.
    Vanhamäki, H.
    Virtanen, I.
    Fabry-Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3709-3728Article in journal (Refereed)
    Abstract [en]

    The high-latitude ionosphere-thermosphere system is strongly affected by the magnetospheric energy input during magnetospheric substorms. In this study, we investigate the response of the upper thermospheric winds to four substorm events by using the Fabry-Perot interferometer at Troms?, Norway, the International Monitor for Auroral Geomagnetic Effects magnetometers, the EISCAT radar, and an all-sky camera. The upper thermospheric winds had distinct responses to substorm phases. During the growth phase, westward acceleration of the wind was observed in the premidnight sector within the eastward electrojet region. We suggest that the westward acceleration of the neutral wind is caused by the ion drag force associated with the large-scale westward plasma convection within the eastward electrojet. During the expansion phase, the zonal wind had a prompt response to the intensification of the westward electrojet (WEJ) overhead Troms?. The zonal wind was accelerated eastward, which is likely to be associated with the eastward plasma convection within the substorm current wedge. During the expansion and recovery phases, the meridional wind was frequently accelerated to the southward direction, when the majority of the substorm WEJ current was located on the poleward side of Troms?. We suggest that this meridional wind acceleration is related to a pressure gradient produced by Joule heating within the substorm WEJ region. In addition, strong atmospheric gravity waves during the expansion and the recovery phases were observed.

  • 37. Carter, J. A.
    et al.
    Milan, S. E.
    Fear, R. C.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hairston, M. R.
    Dayside reconnection under interplanetary magnetic field B-y-dominated conditions: The formation and movement of bending arcs2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 2967-2978Article in journal (Refereed)
    Abstract [en]

    Based upon a survey of global auroral images collected by the Polar Ultraviolet Imager, Kullen etal. (2002) subdivided polar cap auroral arcs into a number of categories, including that of bending arcs. We are concerned with those bending arcs that appear as a bifurcation of the dayside auroral oval and which subsequently form a spur intruding into the polar cap. Once formed, the spur moves poleward and antisunward over the lifetime of the arc. We propose that dayside bending arcs are ionospheric signatures of pulses of dayside reconnection and are therefore part of a group of transient phenomena associated with flux transfer events. We observe the formation and subsequent motion of a bending arc across the polar cap during a 30 min interval on 8 January 1999, and we show that this example is consistent with the proposed model. We quantify the motion of the arc and find it to be commensurate with the convection flows observed by both ground-based radar observations and space-based particle flow measurements. In addition, precipitating particles coincident with the arc appear to occur along open field lines, lending further support to the model.

  • 38. Chen, L. -J
    et al.
    Hesse, M.
    Wang, S.
    Gershman, D.
    Ergun, R. E.
    Burch, J.
    Bessho, N.
    Torbert, R. B.
    Giles, B.
    Webster, J.
    Pollock, C.
    Dorelli, J.
    Moore, T.
    Paterson, W.
    Lavraud, B.
    Strangeway, R.
    Russell, C.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Avanov, L.
    Electron diffusion region during magnetopause reconnection with an intermediate guide field: Magnetospheric multiscale observations2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 5, p. 5235-5246Article in journal (Refereed)
    Abstract [en]

    An electron diffusion region (EDR) in magnetic reconnection with a guide magnetic field approximately 0.2 times the reconnecting component is encountered by the four Magnetospheric Multiscale spacecraft at the Earth's magnetopause. The distinct substructures in the EDR on both sides of the reconnecting current sheet are visualized with electron distribution functions that are 2 orders of magnitude higher cadence than ever achieved to enable the following new findings: (1) Motion of the demagnetized electrons plays an important role to sustain the reconnection current and contributes to the dissipation due to the nonideal electric field, (2) the finite guide field dominates over the Hall magnetic field in an electron-scale region in the exhaust and modifies the electron flow dynamics in the EDR, (3) the reconnection current is in part carried by inflowing field-aligned electrons in the magnetosphere part of the EDR, and (4) the reconnection electric field measured by multiple spacecraft is uniform over at least eight electron skin depths and corresponds to a reconnection rate of approximately 0.1. The observations establish the first look at the structure of the EDR under a weak but not negligible guide field.

  • 39. Chen, L. -J
    et al.
    Hesse, M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Wang, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Gershman, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Bessho, N.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Webster, J.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Pollock, C.
    Denali Sci, Healy, AK USA..
    Dorelli, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Moore, T.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Paterson, W.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, UMR 5277, Toulouse, France..
    Strangeway, R.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Russell, C.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Avanov, L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Electron diffusion region during magnetopause reconnection with an intermediate guide field: Magnetospheric multiscale observations2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 5, p. 5235-5246Article in journal (Refereed)
    Abstract [en]

    An electron diffusion region (EDR) in magnetic reconnection with a guide magnetic field approximately 0.2 times the reconnecting component is encountered by the four Magnetospheric Multiscale spacecraft at the Earth's magnetopause. The distinct substructures in the EDR on both sides of the reconnecting current sheet are visualized with electron distribution functions that are 2 orders of magnitude higher cadence than ever achieved to enable the following new findings: (1) Motion of the demagnetized electrons plays an important role to sustain the reconnection current and contributes to the dissipation due to the nonideal electric field, (2) the finite guide field dominates over the Hall magnetic field in an electron-scale region in the exhaust and modifies the electron flow dynamics in the EDR, (3) the reconnection current is in part carried by inflowing field-aligned electrons in the magnetosphere part of the EDR, and (4) the reconnection electric field measured by multiple spacecraft is uniform over at least eight electron skin depths and corresponds to a reconnection rate of approximately 0.1. The observations establish the first look at the structure of the EDR under a weak but not negligible guide field.

  • 40. Chen, Yuxi
    et al.
    Toth, Gabor
    Cassak, Paul
    Jia, Xianzhe
    Gombosi, Tamas I.
    Slavin, James A.
    Markidis, Stefano
    KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Peng, Ivy Bo
    KTH.
    Jordanova, Vania K.
    Henderson, Michael G.
    Global Three-Dimensional Simulation of Earth's Dayside Reconnection Using a Two-Way Coupled Magnetohydrodynamics With Embedded Particle-in-Cell Model: Initial Results2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 10, p. 10318-10335Article in journal (Refereed)
    Abstract [en]

    We perform a three-dimensional (3-D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle-in-cell model. During the 1 h long simulation, the FTEs are generated quasi-periodically near the subsolar point and move toward the poles. We find that the magnetic field signature of FTEs at their early formation stage is similar to a "crater FTE," which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomes an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. The LHDI electric field is about 8 mV/m, and its dominant wavelength relative to the electron gyroradius agrees reasonably with Magnetospheric Multiscale (MMS) observations.

  • 41.
    Cowley, S. W. H.
    et al.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Provan, G.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Comment on "Magnetic phase structure of Saturn's 10.7h oscillations" by Yates et al.2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 7, p. 5686-5690Article in journal (Other academic)
  • 42.
    Cowley, S. W. H.
    et al.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Zarka, P.
    Univ Paris Diderot, Sorbonne Paris Cite, Univ Paris 06, Univ Paris 04,CNRS,PSL Res Univ,LESIA,Observ Pari, Meudon, France..
    Provan, G.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Lamy, L.
    Univ Paris Diderot, Sorbonne Paris Cite, Univ Paris 06, Univ Paris 04,CNRS,PSL Res Univ,LESIA,Observ Pari, Meudon, France..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Comment on "A new approach to Saturn's periodicities" by J. F. Carbary2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 3, p. 2418-2422Article in journal (Other academic)
  • 43.
    Cravens, T. E.
    et al.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Renzaglia, A.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Plasma Transport in Saturn's Low-Latitude Ionosphere: Cassini Data2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 4881-4888Article in journal (Refereed)
    Abstract [en]

    In 2017 the Cassini Orbiter made the first in situ measurements of the upper atmosphere and ionosphere of Saturn. The Ion and Neutral Mass Spectrometer in its ion mode measured densities of light ion species (H+, H-2(+), H-3(+), and He+), and the Radio and Plasma Wave Science instrument measured electron densities. During proximal orbit 287 (denoted P287), Cassini reached down to an altitude of about 3,000 km above the 1 bar atmospheric pressure level. The topside ionosphere plasma densities measured for P287 were consistent with ionospheric measurements during other proximal orbits. Spacecraft potentials were measured by the Radio and Plasma Wave Science Langmuir probe and are typically about negative 0.3 V. Also, for this one orbit, Ion and Neutral Mass Spectrometer was operated in an instrument mode allowing the energies of incident H+ ions to be measured. H+ is the major ion species in the topside ionosphere. Ion flow speeds relative to Saturn's atmosphere were determined. In the southern hemisphere, including near closest approach, the measured ion speeds were close to zero relative to Saturn's corotating atmosphere, but for northern latitudes, southward ion flow of about 3 km/s was observed. One possible interpretation is that the ring shadowing of the southern hemisphere sets up an interhemispheric plasma pressure gradient driving this flow.

  • 44. Cresswell-Moorcock, Kathy
    et al.
    Rodger, Craig J.
    Kero, Antti
    Collier, Andrew B.
    Clilverd, Mark A.
    Häggström, Ingemar
    Pitkänen, Timo
    A reexamination of latitudinal limits of substorm-produced energetic electron precipitation2013In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, p. 6694-6705Article in journal (Refereed)
  • 45.
    Dahlgren, Hanna
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. University of Southampton, United Kingdom.
    Lanchester, B. S.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Whiter, D. K.
    Electrodynamics and energy characteristics of aurora at high resolution by optical methods2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 6, p. 5966-5974Article in journal (Refereed)
    Abstract [en]

    Technological advances leading to improved sensitivity of optical detectors have revealed that aurora contains a richness of dynamic and thin filamentary structures, but the source of the structured emissions is not fully understood. In addition, high-resolution radar data have indicated that thin auroral arcs can be correlated with highly varying and large electric fields, but the detailed picture of the electrodynamics of auroral filaments is yet incomplete. The Auroral Structure and Kinetics (ASK) instrument is a state-of-the-art ground-based instrument designed to investigate these smallest auroral features at very high spatial and temporal resolution, by using three electron multiplying CCDs in parallel for three different narrow spectral regions. ASK is specifically designed to utilize a new optical technique to determine the ionospheric electric fields. By imaging the long-lived O+ line at 732 nm, the plasma flow in the region can be traced, and since the plasma motion is controlled by the electric field, the field strength and direction can be estimated at unprecedented resolution. The method is a powerful tool to investigate the detailed electrodynamics and current systems around the thin auroral filaments. The two other ASK cameras provide information on the precipitation by imaging prompt emissions, and the emission brightness ratio of the two emissions, together with ion chemistry modeling, is used to give information on the energy and energy flux of the precipitating electrons. In this paper, we discuss these measuring techniques and give a few examples of how they are used to reveal the nature and source of fine-scale structuring in the aurora.

  • 46.
    De Spiegeleer, A.
    et al.
    Umea Univ, Dept Phys, Umea, Sweden..
    Hamrin, M.
    Umea Univ, Dept Phys, Umea, Sweden..
    Gunell, H.
    Umea Univ, Dept Phys, Umea, Sweden.;Belgian Inst Space Aeron, Brussels, Belgium..
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Andersson, L.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Pitkanen, T.
    Umea Univ, Dept Phys, Umea, Sweden.;Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai, Peoples R China..
    Mouikis, C. G.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Nilsson, H.
    Swedish Inst Space Sci, Kiruna, Sweden..
    Kistler, L. M.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 4, p. 2736-2754Article in journal (Refereed)
    Abstract [en]

    Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2-D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0 degrees to 180 degrees in the Northern Hemisphere and from 180 degrees to 0 degrees in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time-of-flight effect from which we estimate that the source of particle is located similar to 5-25R(E) and similar to 40-107R(E) tailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain similar to 21-46 R-E for the Southern Hemisphere event and tailward of X similar to - 65R(E) (outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux.

  • 47.
    De Spiegeleer, Alexandre
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gunell, Herbert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Volwerk, M.
    Andersson, L.
    Karlsson, T.
    Pitkänen, Timo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mouikis, C. G.
    Nilsson, H.
    Kistler, L. M.
    Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 4, p. 2736-2754Article in journal (Refereed)
    Abstract [en]

    Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2-D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0 degrees to 180 degrees in the Northern Hemisphere and from 180 degrees to 0 degrees in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time-of-flight effect from which we estimate that the source of particle is located similar to 5-25R(E) and similar to 40-107R(E) tailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain similar to 21-46 R-E for the Southern Hemisphere event and tailward of X similar to - 65R(E) (outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux.

  • 48.
    De Spiegeleer, Alexandre
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Pitkänen, Timo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Volwerk, M.
    Mann, Ingrid
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics and Technology, The Arctic University of Norway, Tromsø, Norway.
    Nilsson, H.
    Norqvist, Patrik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, L.
    Vaverka, Jakub
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, p. 7042-7056Article in journal (Refereed)
    Abstract [en]

    Using plasma sheet data from Cluster 1 spacecraft from 2001 till 2011, we statistically investigate oscillatory signatures in the plasma bulk flow. These periodic oscillations are compared to high-speed and quiet flows. Periodic oscillations are observed approximately 8% of the time, while high-speed flows and quiet flows are observed around 0.5% and 12% of the time, respectively. We remark that periodic oscillations can roughly occur everywhere for x(gsm) < -10 R-E and |y(gsm)| < 10 RE, while quiet flows mainly occur toward the flanks of this region and toward x = -10 R-E. The relation between the geomagnetic and solar activity and the occurrence of periodic oscillations is investigated and reveal that periodic oscillations occur for most Kp values and solar activity, while quiet flows are more common during low magnetospheric and solar activity. We find that the median oscillation frequency of periodic oscillations is 1.7 mHz and the median duration of the oscillation events is 41 min. We also observe that their associated Poynting vectors show a tendency to be earthward (S-x >= 0). Finally, the distribution of high-speed flows and periodic oscillations as a function of the velocity is investigated and reveals that thresholds lower than 200 km/s should not be used to identify high-speed flows as it could result in misinterpreting a periodic oscillations for a high-speed flow.

  • 49.
    De Spiegeleer, Alexandre
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Volwerk, M.
    Karlsson, T.
    Gunell, Herbert
    Umeå University, Faculty of Science and Technology, Department of Physics. Belgian Institute for Space Aeronomy, Brussels, Belgium.
    Chong, Ghai Siung
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Pitkänen, Timo
    Umeå University, Faculty of Science and Technology, Department of Physics. Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Nilsson, H.
    Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 8928-8942Article in journal (Refereed)
    Abstract [en]

    We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+ data for which the pitch angle continuously changes with time, either from 0 degrees to 180 degrees or from 180 degrees to 0 degrees. These structures are called "Pitch Angle Slope Structures" (PASSes). PASSes for which the pitch angle changes from 0 degrees to 180 degrees are observed in the Northern Hemisphere while those for which the pitch angle changes from 180 degrees to 0 degrees are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth-tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from similar to 0 to similar to 600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy-dispersed structures, the distance to the source from the spacecraft is estimated to be typically R-E along the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail.

  • 50. Deca, Jan
    et al.
    Divin, Andrey
    Lembege, Bertrand
    Horanyi, Mihaly
    Markidis, Stefano
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Lapenta, Giovanni
    General mechanism and dynamics of the solar wind interaction with lunar magnetic anomalies from 3-D particle-in-cell simulations2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 8, p. 6443-6463Article in journal (Refereed)
    Abstract [en]

    We present a general model of the solar wind interaction with a dipolar lunar crustal magnetic anomaly (LMA) using three-dimensional full-kinetic and electromagnetic simulations. We confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface, forming a so-called minimagnetosphere, as suggested by spacecraft observations and theory. We show that the LMA configuration is driven by electron motion because its scale size is small with respect to the gyroradius of the solar wind ions. We identify a population of back-streaming ions, the deflection of magnetized electrons via the E x B drift motion, and the subsequent formation of a halo region of elevated density around the dipole source. Finally, it is shown that the presence and efficiency of the processes are heavily impacted by the upstream plasma conditions and, on their turn, influence the overall structure and evolution of the LMA system. Understanding the detailed physics of the solar wind interaction with LMAs, including magnetic shielding, particle dynamics and surface charging is vital to evaluate its implications for lunar exploration.

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