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  • 1.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Lindkvist, Jesper
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Swedish Institute of Space Physics, Kiruna.
    Götz, C.
    Technicsche Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft. Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind. Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere. Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind. Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind

  • 2.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Brolles, T.W.
    Space Science and Engineering Division, Southwest Research Institute, San Antonio.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mass loading at 67P/Churyumov-Gerasimenko: A case study2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 4, p. 1411-1418Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.

  • 3.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 2, p. 1570-1575Article in journal (Refereed)
    Abstract [en]

    When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.

  • 4.
    Berecic, Laura
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nicolaou, G.
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Wieser, M.
    Swedish Institute of Space Physics, Kiruna.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

  • 5.
    Dieval, Catherine
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Edberg, N.J.T.
    Swedish Institute of Space Physics, Uppsala.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Reduced proton and alpha particle precipitations at Mars during solar wind pressure pulses: Mars Express results2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3421-3429Article in journal (Refereed)
    Abstract [en]

    1] We performed a statistical study of downward moving protons and alpha particles of ~keV energy (assumed to be of solar wind origin) inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package on board Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low-altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent, and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses, the occurrence frequency of observed proton precipitation events is reduced by a factor of ~3, and for He2+ events the occurrence frequency is reduced by a factor of ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pileup of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H+/He2+ precipitations.

  • 6.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Emami, Reza
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Törlind, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zorzano Mier, Maria-Paz
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Parida, Vinit
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dordlofva, Christo
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Mendaza de Cal, Maria Teresa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Roos, Tobias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ottemark, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nieto, Chris
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Soria Salinas, Álvaro Tomás
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vázquez Martín, Sandra
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neikter, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindwall, Angelica
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Fakhardji, Wissam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Projekt: Rymdforskarskolan2015Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The Graduate School of Space Technology

  • 7.
    Kirkwood, Sheila
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Belova, Evgenia G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Dalin, Peter A.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Mihalikova, Maria
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Mikhaylova, Daria
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Murtagh, Donal P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Satheesan, K.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Urban, Joachim B.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Wolf, Ingemar
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: The importance of nitric oxide2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, no 2, p. 333-347Article in journal (Refereed)
    Abstract [en]

    The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic I K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68 N, geomagnetic latitude 65 ) and at two different sites in Queen Maud Land, Antarctica (73/72 S, geomagnetic latitudes 62/63 ). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and indices) and low correlations for minute-to-day timescales

  • 8.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barghouthi, Imad A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Eriksson, A.I
    Swedish Institute of Space Physics, Uppsala.
    André, M.
    Swedish Institute of Space Physics, Uppsala.
    Hot and cold ion outflow: Observations and implications for numerical models2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, p. 105-117Article in journal (Refereed)
    Abstract [en]

    Cluster observations of oxygen ion outflow and low-frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low-altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high-energy O+ ions in the high-altitude cusp and mantle and cold H+ ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high-altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O+ and cold H+, if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low-altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations

  • 9.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Hamrin, Maria
    Department of Physics, Umeå University.
    Pitkänen, Timo
    Department of Physics, Umeå University.
    Karlsson, Tomas
    Space and Plasma Physics, School of Electrical Engineering Royal Institute of Technology Stockholm.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Andersson, Laila O.
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vaivads, Andris
    Swedish Institute of Space Physics, Uppsala.
    Oxygen ion response to proton bursty bulk flows2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 8, p. 7535-7546Article in journal (Refereed)
    Abstract [en]

    We have used Cluster spacecraft data from the years 2001 to 2005 to study how oxygen ions respond to bursty bulk flows (BBFs) as identified from proton data. We here define bursty bulk flows as periods of proton perpendicular velocities more than 100 km/s and a peak perpendicular velocity in the structure of more than 200 km/s, observed in a region with plasma beta above 1 in the near-Earth central tail region. We find that during proton BBFs only a minor increase in the O+ velocity is seen. The different behavior of the two ion species is further shown by statistics of H+ and O+ flow also outside BBFs: For perpendicular earthward velocities of H+ above about 100 km/s, the O+ perpendicular velocity is consistently lower, most commonly being a few tens of kilometers per second earthward. In summary, O+ ions in the plasma sheet experience less acceleration than H+ ions and are not fully frozen in to the magnetic field. Therefore, H+ and O+ motion is decoupled, and O+ ions have a slower earthward motion. This is particularly clear during BBFs. This may add further to the increased relative abundance of O+ ions in the plasma sheet during magnetic storms. The data indicate that O+ is typically less accelerated in association with plasma sheet X lines as compared to H+.

  • 10.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Barghouthi, I.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Eriksson, A.I.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    André, M.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Hot and cold ion outflow: Spatial distribution of ion heating2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    Ions apparently emanating from the same source, the ionospheric polar cap, can either end up as energized to keV energies in the high-altitude cusp/mantle, or appear as cold ions in the magnetotail lobes. We use Cluster observations of ions and wave electric fields to study the spatial variation of ion heating in the cusp/mantle and polar cap. The average flow direction in a simplified cylindrical coordinate system is used to show approximate average ion flight trajectories, and discuss the temperatures, fluxes and wave activity along some typical trajectories. It is found that it is suitable to distinguish between cusp, central and nightside polar cap ion outflow trajectories, though O+ heating is mainly a function of altitude. Furthermore we use typical cold ion parallel velocities and the observed average perpendicular drift to obtain average cold ion flight trajectories. The data show that the cusp is the main source of oxygen ion outflow, whereas a polar cap source would be consistent with our average outflow paths for cold ions observed in the lobes. A majority of the cusp O+ flux is sufficiently accelerated to escape into interplanetary space. A scenario with significant oxygen ion heating in regions with strong magnetosheath origin ion fluxes, cold proton plasma dominating at altitudes below about 8 RE in the polar cap, and most of the cusp oxygen outflow overcoming gravity and flowing out in the cusp and mantle is consistent with our observations.

  • 11.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gunell, Herbert
    Belgian Institute for Space Aeronomy, Brussels.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics.
    Lundin, Rickard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Swedish Institute of Space Physics.
    Wieser, Martin
    Swedish Institute of Space Physics.
    Carr, Chris
    Imperial College London.
    Cupido, Emanuele
    Imperial College London.
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Savaud, Jean-André
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Koskinen, Hannu
    Department of Physics, University of Helsinki.
    Kallio, Esa
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Lebreton, Jean-Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E).
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory.
    Edberg, Niklas
    Swedish Institute of Space Physics, Ångström Laboratory.
    Goldstein, Raymond
    Belgian Institute for Space Aeronomy, Brussels.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E).
    Coenders, Christoph
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Rubin, Martin
    Physikalisches Institut, University of Bern.
    Birth of a comet magnetosphere: A spring of water ions2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, no 6220, article id aaa0571Article in journal (Refereed)
    Abstract [en]

    The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (

  • 12.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Edberg, N.J.T.
    Swedish Institute of Space Physics, Uppsala.
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics.
    Koenders, Christoph
    Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig.
    Wieser, Martin
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Lundin, Rickard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Mandt, Kathleen E.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Goldstein, Raymond M.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Carr, Chris
    Imperial College London.
    Cupido, Emanuele
    Imperial College London.
    Fox, P.T.
    Imperial College London.
    Szego, Karoly
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Sauvaud, J.A.
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Koskinen, Hannu
    Department of Physics, University of Helsinki.
    Geiger, B.
    Rosetta Science Ground Segment, Science and Robotic Exploration (SRE-OOR).
    Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, article id A20Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, where the comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation. Aims. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ion environment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energy are abundant. We compare ion fluxes of solar wind and cometary origin. Methods. RPC-ICA is an ion mass spectrometer measuring ions of solar wind and cometary origins in the 10 eV-40 keV energy range. Results. We show how the flux of accelerated water ions with energies above 120 eV increases between 3.6 and 2.0 AU. The 24 h average increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectra also become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion flux is frequently of the same order as the solar wind proton flux. Water ions of 120 eV-few keV energy may thus constitute a significant part of the ions sputtering the nucleus surface. The ion density and mass in the comet vicinity is dominated by ions of cometary origin. The solar wind is deflected and the energy spectra broadened compared to an undisturbed solar wind.

  • 13.
    Nordström, T.
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Zhang, T.L.
    Austrian Academy of Sciences, Space Research Institute, Graz.
    Venus ion outflow estimates at solar minimum: Influence of reference frames and disturbed solar wind conditions2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3592-3601Article in journal (Refereed)
    Abstract [en]

    Recent estimates of ion escape rates from Venus, based on ASPERA-4 data, differ by more than a factor of 4. Whereas the ASPERA-4 instrument provides state-of-the art observations, the limited field of view of the instrument and the strongly limited geographical coverage of the spacecraft orbit means that significant assumptions must be used in the interpretation of the data. We complement previous studies by using a method of average distribution functions to obtain as good statistics as possible while taking the limited field of view into account. We use more than 3 years of data, more than any of the previous studies, and investigate how the choice of a geographical reference frame or a solar wind electric field oriented reference frame affects the results. We find that the choice of reference frame cannot explain the difference between the previously published reports. Our results, based on a larger data set, fall in between the previous studies. Our conclusion is that the difference between previous studies is caused by the large variability of ion outflow at Venus. It matters significantly for the end result which data are selected and which time period is used. The average escape rates were found to be 5.2±1.0×1024 s−1for heavy ions (m/q ≥16) and 14±2.6×1024 s−1for protons. We also discuss the spatial distribution of the planetary ion outflow in the solar wind electric field reference frame.

  • 14.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Slapak, R.
    EISCAT Scientific Association, Kiruna, Sweden.
    Wintoft, P.
    Swedish Institute of Space Physics, Lund, Sweden.
    Yamauchi, M.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Wik, M.
    Swedish Institute of Space Physics, Lund, Sweden.
    Dandouras, I.
    IRAP, Université de Toulouse, CNRS, UPS, CNES, France.
    Carr, C.M.
    Department of Physics, Imperial College London, London, United Kingdom.
    O+ Escape During the Extreme Space Weather Event of 4–10 September 20172018In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, no 9, p. 1363-1376Article in journal (Refereed)
    Abstract [en]

    We have investigated the consequences of extreme space weather on ion outflow from the polar ionosphere by analyzing the solar storm that occurred early September 2017, causing a severe geomagnetic storm. Several X-flares and coronal mass ejections were observed between 4 and 10 September. The first shock—likely associated with a coronal mass ejection—hit the Earth late on 6 September, produced a storm sudden commencement, and began the initial phase of the storm. It was followed by a second shock, approximately 24 hr later, that initiated the main phase and simultaneously the Dst index dropped to Dst = −142 nT and Kp index reached Kp = 8. Using COmposition DIstribution Function data on board Cluster satellite 4, we estimated the ionospheric O+ outflow before and after the second shock. We found an enhancement in the polar cap by a factor of 3 for an unusually high ionospheric O+ outflow (mapped to an ionospheric reference altitude) of 1013 m−2 s−1. We suggest that this high ionospheric O+ outflow is due to a preheating of the ionosphere by the multiple X-flares. Finally, we briefly discuss the space weather consequences on the magnetosphere as a whole and the enhanced O+ outflow in connection with enhanced satellite drag.

  • 15.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Atmospheric loss during major geomagnetic storms: Cluster observations2017Conference paper (Refereed)
  • 16.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Hamrin, Maria
    Department of Physics, Umeä University.
    Pitkänen, Timo
    Department of Physics, Umeä University.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Karlsson, Tomas
    Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Quantification of the total ion transport in the near-Earth plasma sheet2017In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 4, p. 869-877Article in journal (Refereed)
    Abstract [en]

    Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001-2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s -1, respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0. 5 × 1025 s -1, which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows ( < 100kms -1) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

  • 17.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Schillings, Audrey
    Swedish Institute of Space Physics, Kiruna.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dandouras, Iannis
    CNSR, Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Atmospheric outflow from the terrestrial magnetosphere: implications forescape on evolutionary time scales2017Conference paper (Refereed)
  • 18.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A statistical study on O+ flux in the dayside magnetosheath2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1005-1010Article in journal (Refereed)
    Abstract [en]

    Studies on terrestrial oxygen ion (O+) escape into the interplanetary space have considered a number of different escape paths. Recent observations however suggest a yet insufficiently investigated additional escape route for hot O+: along open magnetic field lines in the high altitude cusp and mantle. Here we present a statistical study on O+ flux in the high-latitude dayside magnetosheath. The O+ is generally seen relatively close to the magnetopause, consistent with observations of O+ flowing primarily tangentially to the magnetopause. We estimate the total escape flux in this region to be ~ 7 × 1024 s−1, implying this escape route to significantly contribute to the overall total O+ loss into interplanetary space.

  • 19.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eriksson, Anders
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Observations of oxygen ions in the dayside magnetosheath associated with southward IMF2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    We present a case study of high energy oxygen ions (O+) observed in the dayside terrestrial magnetosheath, in the southern hemisphere. It is shown that the presence of O+ is strongly correlated to the IMF direction: O+ is observed only for Bz<0. Three satellites observe O$^+ immediately at both sides of the magnetopause and about 2 RE outside the magnetopause. These conditions indicate escape along open magnetic field lines. We show that if outflowing O+ is heated and accelerated sufficiently in the cusp, it takes 15-20 minutes for it to reach the magnetopause, allowing the ions to escape along newly opened field lines on the dayside. Earlier studies show evidence of strong heating and high velocities in the cusp and mantle at high altitudes, strengthening our interpretation. The observed magnetosheath O+ fluxes are of the same order as measured in the ionospheric upflow, which indicates that this loss mechanism is significant when it takes place.

  • 20.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Richard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    O+ transport in the dayside magnetosheath and its dependence on the IMF direction2015In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, p. 301-307Article in journal (Refereed)
    Abstract [en]

    Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

  • 21.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales2017In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 3, p. 721-731Article in journal (Refereed)
  • 22.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,20172018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Article in journal (Refereed)
  • 23.
    Waara, Martin
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Slapak, Rikard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    André, Mats
    Institutet för rymdfysik, Uppsala.
    Stenberg, Gabriella
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Oxygen ion energization by waves in the high altitude cusp and mantle2012In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, p. 1309-1314Article in journal (Refereed)
  • 24.
    Wedlund, Cyril Simon
    et al.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Alho, Markku
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Pusa, J.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gronoff, Guillaume
    Science Directorate, Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, Virginia.
    The atmosphere of comet 67P/Churyumov-Gerasimenko diagnosed by charge-exchanged solar wind alpha particles2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A154Article in journal (Refereed)
    Abstract [en]

    Context. The ESA/Rosetta mission has been orbiting comet 67P/Churyumov-Gerasimenko since August 2014, measuring its dayside plasma environment. The ion spectrometer onboard Rosetta has detected two ion populations, one energetic with a solar wind origin (H+, He2+, He+), the other at lower energies with a cometary origin (water group ions such as H2O+). He+ ions arise mainly from charge-exchange between solar wind alpha particles and cometary neutrals such as H2O. Aims. The He+ and He2+ ion fluxes measured by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA) give insight into the composition of the dayside neutral coma, into the importance of charge-exchange processes between the solar wind and cometary neutrals, and into the way these evolve when the comet draws closer to the Sun. Methods. We combine observations by the ion spectrometer RPC-ICA onboard Rosetta with calculations from an analytical model based on a collisionless neutral Haser atmosphere and nearly undisturbed solar wind conditions. Results. Equivalent neutral outgassing rates Q can be derived using the observed RPC-ICA He+/He2+ particle flux ratios as input into the analytical model in inverse mode. A revised dependence of Q on heliocentric distance Rh in AU is found to be Rh -7.06Rh-7.06 between 1.8 and 3.3 AU, suggesting that the activity in 2015 differed from that of the 2008 perihelion passage. Conversely, using an outgassing rate determined from optical remote sensing measurements from Earth, the forward analytical model results are in relatively good agreement with the measured RPC-ICA flux ratios. Modelled ratios in a 2D spherically-symmetric plane are also presented, showing that charge exchange is most efficient with solar wind protons. Detailed cometocentric profiles of these ratios are also presented. Conclusions. In conclusion, we show that, with the help of a simple analytical model of charge-exchange processes, a mass-capable ion spectrometer such as RPC-ICA can be used as a "remote-sensing" instrument for the neutral cometary atmosphere.

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