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  • 1.
    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.

  • 2.
    Ala-Lahti, Matti M.
    et al.
    Univ Helsinki, Dept Phys, POB 64, Helsinki, Finland.
    Kilpua, Emilia K. J.
    Univ Helsinki, Dept Phys, POB 64, Helsinki, Finland.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Aalto Univ, Sch Elect Engn, Espoo, Finland.
    Osmane, Adnane
    Aalto Univ, Sch Elect Engn, Espoo, Finland.
    Pulkkinen, Tuija
    Aalto Univ, Sch Elect Engn, Espoo, Finland.
    Soucek, Jan
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic.
    Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection2018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, no 3, p. 793-808Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME). We have constructed a semi-automated method to identify mirror modes from the magnetic field data. We analyze 91 ICME sheath regions from January 1997 to April 2015 using data from the Wind spacecraft. The results imply that similarly to planetary magnetosheaths, mirror modes are also common structures in ICME sheaths. However, they occur almost exclusively as dip-like structures and in mirror stable plasma. We observe mirror modes throughout the sheath, from the bow shock to the ICME leading edge, but their amplitudes are largest closest to the shock. We also find that the shock strength (measured by Alfven Mach number) is the most important parameter in controlling the occurrence of mirror modes. Our findings suggest that in ICME sheaths the dominant source of free energy for mirror mode generation is the shock compression. We also suggest that mirror modes that are found deeper in the sheath are remnants from earlier times of the sheath evolution, generated also in the vicinity of the shock.

  • 3.
    Blanco-Cano, Xochitl
    et al.
    Univ Nacl Autonoma Mexico, Inst Geofis, Mexico City, DF, Mexico..
    Battarbee, Markus
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Turc, Lucile
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland..
    Kilpua, Emilia K. J.
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Hoilijoki, Sanni
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Ganse, Urs
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Sibeck, David G.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Cassak, Paul A.
    West Virginia Univ, Dept Phys & Astron, Morgantown, WV USA..
    Fear, Robert C.
    Univ Southampton, Dept Phys & Astron, Southampton, Hants, England..
    Jarvinen, Riku
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.;Finnish Meteorol Inst, Helsinki, Finland..
    Juusola, Liisa
    Univ Helsinki, Dept Phys, Helsinki, Finland.;Finnish Meteorol Inst, Helsinki, Finland..
    Pfau-Kempf, Yann
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Vainio, Rami
    Univ Turku, Dept Phys & Astron, Turku, Finland..
    Palmroth, Minna
    Univ Helsinki, Dept Phys, Helsinki, Finland.;Finnish Meteorol Inst, Helsinki, Finland..
    Cavitons and spontaneous hot flow anomalies in a hybrid-Vlasov global magnetospheric simulation2018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, no 4, p. 1081-1097Article in journal (Refereed)
    Abstract [en]

    In this paper we present the first identification of foreshock cavitons and the formation of spontaneous hot flow anomalies (SHFAs) with the Vlasiator global magnetospheric hybrid-Vlasov simulation code. In agreement with previous studies we show that cavitons evolve into SHFAs. In the presented run, this occurs very near the bow shock. We report on SHFAs surviving the shock crossing into the down-stream region and show that the interaction of SHFAs with the bow shock can lead to the formation of a magnetosheath cavity, previously identified in observations and simulations. We report on the first identification of long-term local weakening and erosion of the bow shock, associated with a region of increased foreshock SHFA and caviton formation, and repeated shock crossings by them. We show that SHFAs are linked to an increase in suprathermal particle pitch-angle spreads. The realistic length scales in our simulation allow us to present a statistical study of global caviton and SHFA size distributions, and their comparable size distributions support the theory that SHFAs are formed from cavitons. Virtual spacecraft observations are shown to be in good agreement with observational studies.

  • 4.
    Dimmock, Andrew P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.
    Alho, M.
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.
    Kallio, Esa
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.
    Pope, Simon Alexander
    Univ Sheffield, Dept Automat Control & Syst Engn, Sheffield, S Yorkshire, England.
    Zhang, Tielong
    Harbin Inst Technol, Shenzhen, Peoples R China; Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Kilpua, E.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Pulkkinen, Tuija I.
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.
    Futaana, Y.
    Swedish Inst Space Phys, Kiruna, Sweden.
    Coates, Andrew J.
    UCL, Mullard Space Sci Lab, London, England.
    The Response of the Venusian Plasma Environment to the Passage of an ICME: Hybrid Simulation Results and Venus Express Observations2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 5, p. 3580-3601Article in journal (Refereed)
    Abstract [en]

    Owing to the heritage of previous missions such as the Pioneer Venus Orbiter and Venus Express, the typical global plasma environment of Venus is relatively well understood. On the other hand, this is not true for more extreme driving conditions such as during passages of interplanetary coronal mass ejections (ICMEs). One of the outstanding questions is how do ICMEs, either the ejecta or sheath portions, impact (1) the Venusian magnetic topology and (2) escape rates of planetary ions? One of the main issues encountered when addressing these problems is the difficulty of inferring global dynamics from single spacecraft obits; this is where the benefits of simulations become apparent. In the present study, we present a detailed case study of an ICME interaction with Venus on 5 November 2011 in which the magnetic barrier reached over 250 nT. We use both Venus Express observations and hybrid simulation runs to study the impact on the field draping pattern and the escape rates of planetary O+ ions. The simulation showed that the magnetic field line draping pattern around Venus during the ICME is similar to that during typical solar wind conditions and that O+ ion escape rates are increased by approximately 30% due to the ICME. Moreover, the atypically large magnetic barrier appears to manifest from a number of factors such as the flux pileup, dayside compression, and the driving time from the ICME ejecta.

  • 5.
    Dimmock, Andrew P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Rosenqvist, L.
    Swedish Def Res Agcy, Stockholm, Sweden.
    Hall, J-O
    Swedish Def Res Agcy, Stockholm, Sweden;Swedish Nucl Fuel & Waste Management Co, Solna, Sweden.
    Viljanen, A.
    Finnish Meteorol Inst, Helsinki, Finland.
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Honkonen, I
    Finnish Meteorol Inst, Helsinki, Finland.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sjoberg, E. C.
    Swedish Inst Space Phys, Kiruna, Sweden.
    The GIC and Geomagnetic Response Over Fennoscandia to the 7-8 September 2017 Geomagnetic Storm2019In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 17, no 7, p. 989-1010Article in journal (Refereed)
    Abstract [en]

    Between 7 and 8 September 2017, Earth experienced extreme space weather events. We have combined measurements made by the IMAGE magnetometer array, ionospheric equivalent currents, geomagnetically induced current (GIC) recordings in the Finnish natural gas pipeline, and multiple ground conductivity models to study the Fennoscandia ground effects. This unique analysis has revealed multiple interesting physical and technical insights. We show that although the 7-8 September event was significant by global indices (Dst similar to 150 nT), it produced an unexpectedly large peak GIC. It is intriguing that our peak GIC did not occur during the intervals of largest geomagnetic depressions, nor was there any clear upstream trigger. Another important insight into this event is that unusually large and rare GIC amplitudes (>10 A) occurred in multiple Magnetic Local Time (MLT) sectors and could be associated with westward and eastward electrojets. We were also successfully able to model the geoelectric field and GIC using multiple models, thus providing a further important validation of these models for an extreme event. A key result from our multiple conductivity model comparison was the good agreement between the temporal features of 1-D and 3-D model results. This provides an important justification for past and future uses of 1-D models at Mantsala which is highly relevant to additional uses of this data set. Although the temporal agreement (after scaling) was good, we found a large (factor of 4) difference in the amplitudes between local and global ground models due to the difference in model conductivities. Thus, going forward, obtaining accurate ground conductivity values are key for GIC modeling.

  • 6.
    Dimmock, Andrew P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.
    Sagdeev, Roald Z.
    Univ Maryland, Dept Phys, College Pk, MD 20742 USA.
    Krasnoselskikh, Vladimir
    Univ Orleans, CNRS, LPC2E, Orleans, France;Univ Calif Berkeley, Space Sci Lab, 7 Gauss Way, Berkeley, CA 94720 USA.
    Walker, Simon N.
    Univ Sheffield, Dept Automat Control & Syst Engn, Sheffield, S Yorkshire, England.
    Carr, Christopher
    Imperial Coll London, London SW7 2AZ, England.
    Dandouras, Iannis
    Univ Toulouse, IRAP, CNRS, UPS,CNES, Toulouse, France.
    Escoubet, C. Philippe
    European Space Agcy, European Space Res & Technol Ctr ESA ESTEC, Noordwijk, Netherlands.
    Ganushkina, Natalia
    Finnish Meteorol Inst, Helsinki, Finland;Univ Michigan, Ann Arbor, MI 48109 USA.
    Gedalin, Michael
    Ben Gurion Univ Negev, Dept Phys, Beer Sheva, Israel.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Aryan, Homayon
    Univ Sheffield, Dept Automat Control & Syst Engn, Sheffield, S Yorkshire, England;NASA Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Pulkkinen, Tuija, I
    Univ Michigan, Ann Arbor, MI 48109 USA;Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Espoo, Finland.
    Balikhin, Michael A.
    Univ Sheffield, Dept Automat Control & Syst Engn, Sheffield, S Yorkshire, England.
    Direct evidence of nonstationary collisionless shocks in space plasmas2019In: Science Advances, E-ISSN 2375-2548, Vol. 5, no 2, article id eaau9926Article in journal (Refereed)
    Abstract [en]

    Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.

  • 7.
    Hoilijoki, S.
    et al.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA;Univ Helsinki, Dept Phys, Helsinki, Finland.
    Ganse, U.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Sibeck, D. G.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Cassak, P. A.
    West Virginia Univ, Dept Phys & Astron, Morgantown, WV 26506 USA.
    Turc, L.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Battarbee, M.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Fear, R. C.
    Univ Southampton, Dept Phys & Astron, Southampton, Hants, England.
    Blanco-Cano, X.
    Univ Nacl Autonoma Mexico, Inst Geofis, Mexico City, DF, Mexico.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Aalto Univ, Dept Elect & Nanoengn, Sch Elect Engn, Espoo, Finland.
    Kilpua, E. K. J.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Jarvinen, R.
    Aalto Univ, Dept Elect & Nanoengn, Sch Elect Engn, Espoo, Finland;Finnish Meteorol Inst, Helsinki, Finland.
    Juusola, L.
    Univ Helsinki, Dept Phys, Helsinki, Finland;Finnish Meteorol Inst, Helsinki, Finland.
    Pfau-Kempf, Y.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Palmroth, M.
    Univ Helsinki, Dept Phys, Helsinki, Finland;Finnish Meteorol Inst, Helsinki, Finland.
    Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 4037-4048Article in journal (Refereed)
    Abstract [en]

    This paper describes properties and behavior of magnetic reconnection and flux transfer events (FTEs) on the dayside magnetopause using the global hybrid-Vlasov code Vlasiator. We investigate two simulation runs with and without a sunward (positive)B-x component of the interplanetary magnetic field (IMF) when the IMF is southward. The runs are two-dimensional in real space in the noon-midnight meridional (polar) plane and three-dimensional in velocity space. Solar wind input parameters are identical in the two simulations with the exception that the IMF is purely southward in one but tilted 45 degrees toward the Sun in the other. In the purely southward case (i.e., without B-x) the magnitude of the magnetos heath magnetic field component tangential to the magnetopause is larger than in the run with a sunward tilt. This is because the shock normal is perpendicular to the IMF at the equatorial plane, whereas in the other run the shock configuration is oblique and a smaller fraction of the total IMF strength is compressed at the shock crossing. Hence, the measured average and maximum reconnection rate are larger in the purely southward run. The run with tilted IMF also exhibits a north-south asymmetry in the tangential magnetic field caused by the different angle between the IMF and the bow shock normal north and south of the equator. Greater north-south asymmetries are seen in the FTE occurrence rate, size, and velocity as well; FTEs moving toward the Southern Hemisphere are larger in size and observed less frequently than FTEs in the Northern Hemisphere.

  • 8.
    Lakka, A.
    et al.
    Aalto Univ, Dept Elect & Nanoengn, Espoo, Finland.
    Pulkkinen, T. I.
    Aalto Univ, Dept Elect & Nanoengn, Espoo, Finland.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Myllys, M.
    Univ Helsinki, Dept Phys, Helsinki, Finland; CNRS, Lab Phys & Chim Environm & Espace, Orleans, France.
    Honkonen, I.
    Finnish Meteorol Inst, Helsinki, Finland.
    Palmroth, M.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    The Cross-Polar Cap Saturation in GUMICS-4 During High Solar Wind Driving2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 5, p. 3320-3332Article in journal (Refereed)
    Abstract [en]

    It is well known that the Earth's ionospheric cross‐polar cap potential (CPCP) saturates as a response to the solar wind (SW) driver especially when the level of driving is high and the interplanetary magnetic field is oriented southward. Moreover, previous studies have shown that the upstream Alfvén Mach number may be an important factor in the saturation effect. While the CPCP is often viewed as a measure of the SW‐magnetosphere‐ionosphere coupling, the processes associated with the nonlinearity of the coupling remain an open issue. We use fourth edition of the Grand Unified Magnetosphere‐Ionosphere Coupling Simulation (GUMICS‐4) and artificial SW data to mimic weak and strong driving in order to study the CPCP response to a wide range of interplanetary magnetic field magnitudes (3.5–30 nT) and upstream Alfvén Mach number values (1.2–22). The results provide the first overview of the CPCP saturation in GUMICS‐4 and show that the onset of saturation is strongly dependent on the upstream Alfvén Mach number and the physical processes responsible for the saturation effect might take place both in the Earth's magnetosheath and in the upstream SW.

  • 9.
    Lakka, Antti
    et al.
    Aalto Univ, Dept Elect & Nanoengn, Espoo, Finland.
    Pulkkinen, Tuija I.
    Aalto Univ, Dept Elect & Nanoengn, Espoo, Finland;Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Kilpua, Emilia
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Ala-Lahti, Matti
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Honkonen, Ilja
    Finnish Meteorol Inst, Helsinki, Finland.
    Palmroth, Minna
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Raukunen, Osku
    Univ Turku, Dept Phys & Astron, Turku, Finland.
    GUMICS-4 analysis of interplanetary coronal mass ejection impact on Earth during low and typical Mach number solar winds2019In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 37, no 4, p. 561-579Article in journal (Refereed)
    Abstract [en]

    We study the response of the Earth's magnetosphere to fluctuating solar wind conditions during interplanetary coronal mass ejections (ICMEs) using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). The two ICME events occurred on 15-16 July 2012 and 29-30 April 2014. During the strong 2012 event, the solar wind upstream values reached up to 35 particles cm(-3), speeds of up to 694 km s(-1), and an interplanetary magnetic field of up to 22 nT, giving a Mach number of 2.3. The 2014 event was a moderate one, with the corresponding upstream values of 30 particles cm(-3), 320 km s(-1) and 10 nT, indicating a Mach number of 5.8. We examine how the Earth's space environment dynamics evolves during both ICME events from both global and local perspectives, using well-established empirical models and in situ measurements as references. We show that on the large scale, and during moderate driving, the GUMICS-4 results are in good agreement with the reference values. However, the local values, especially during high driving, show more variation: such extreme conditions do not reproduce local measurements made deep inside the magnetosphere. The same appeared to be true when the event was run with another global simulation. The cross-polar cap potential (CPCP) saturation is shown to depend on the Alfven-Mach number of the upstream solar wind. However, care must be taken in interpreting these results, as the CPCP is also sensitive to the simulation resolution.

  • 10.
    Osmane, Adnane
    et al.
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Pulkkinen, Tuija, I
    Univ Michigan, Dept Climate & Space Sci, Ann Arbor, MI 48109 USA;Aalto Univ, Sch Elect Engn, Espoo, Finland.
    Jensen-Shannon Complexity and Permutation Entropy Analysis of Geomagnetic Auroral Currents2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 4, p. 2541-2551Article in journal (Refereed)
    Abstract [en]

    In this study we determine whether auroral westward currents can be characterized by low-dimensional chaotic attractors through the use of the complexity-entropy methodology developed by Rosso et al. (2007, https:// doi.org/10.1103/PhysRevLett.99.154102) and based on the permutation entropy developed by Bandt and Pompe (2002, https://doi.org/10.1103/PhysRevLett.88.174102) . Our results indicate that geomagnetic auroral indices are indistinguishable from stochastic processes from time scales ranging from a few minutes to 10 hr and for embedded dimensions d < 8. Our results are inconsistent with earlier studies of Baker et al. (1990, https://doi.org/10.1029/GL017i001p00041), Pavlos et al. (1992), D. Roberts et al. (1991, https://doi.org/10.1029/91GL00021), D. A. Roberts (1991, https://doLorg/10.1029/91JA01088), and Vassiliadis et al. (1990, https://doi.org/10.1029/GL017i011 p01841, 1991, https://doi.org/10.1029/91GL01378) indicating that auroral geomagnetic indices could be reduced to low-dimensional systems with chaotic dynamics.

  • 11.
    Werner, A. L. E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Sorbonne Univ, CNRS, LATMOS IPSL, UVSQ, Paris, France.
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden.
    Temmer, M.
    Karl Franzens Univ Graz, Inst Phys, Graz, Austria.
    Modeling the Multiple CME Interaction Event on 6-9 September 2017 with WSA-ENLIL plus Cone2019In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 17, no 2, p. 357-369Article in journal (Refereed)
    Abstract [en]

    A series of coronal mass ejections (CMEs) erupted from the same active region between 4-6 September 2017. Later, on 6-9 September, two interplanetary (IP) shocks reached LE creating a complex and geoeffective plasma structure. To understand the processes leading up to the formation of the two shocks, we model the CMEs with the Wang-Sheeley-Arge (WSA)-ENLIL+Cone model. The first two CMEs merged already in the solar corona driving the first IP shock. In IP space, another fast CME presumably interacted with the flank of the preceding CMEs and caused the second shock detected in situ. By introducing a customized density enhancement factor (dcld) in the WSA-ENLIL+Cone model based on coronagraph image observations, the predicted arrival time of the first IP shock was drastically improved. When the dcld factor was tested on a well-defined single CME event from 12 July 2012 the shock arrival time saw similar improvement. These results suggest that the proposed approach may be an alternative to improve the forecast for fast and simple CMEs. Further, the slowly decelerating kilometric type II radio burst confirms that the properties of the background solar wind have been preconditioned by the passage of the first IP shock. This likely caused the last CME to experience insignificant deceleration and led to the early arrival of the second IP shock. This result emphasizes the need to take preconditioning of the IP medium into account when making forecasts of CMEs erupting in quick succession.

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