Browsing by Subject "SOLAR-WIND"

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  • Milillo, A.; Fujimoto, M.; Murakami, G.; Benkhoff, J.; Zender, J.; Aizawa, S.; Dosa, M.; Griton, L.; Heyner, D.; Ho, G.; Imber, S. M.; Jia, Yan; Karlsson, T.; Killen, R. M.; Laurenza, M.; Lindsay, S. T.; McKenna-Lawlor, S.; Mura, A.; Raines, J. M.; Rothery, D. A.; Andre, N.; Baumjohann, W.; Berezhnoy, A.; Bourdin, P. A.; Bunce, E. J.; Califano, F.; Deca, J.; de la Fuente, S.; Dong, C.; Grava, C.; Fatemi, S.; Henri, P.; Ivanovski, S. L.; Jackson, B. V.; James, M.; Kallio, E.; Kasaba, Y.; Kilpua, E.; Kobayashi, M.; Langlais, B.; Leblanc, F.; Lhotka, C.; Mangano, V.; Martindale, A.; Massetti, S.; Masters, A.; Morooka, M.; Narita, Y.; Oliveira, J. S.; Odstrcil, D.; Orsini, S.; Pelizzo, M. G.; Plainaki, C.; Plaschke, F.; Sahraoui, Afaf; Seki, K.; Slavin, J. A.; Vainio, R.; Wurz, P.; Barabash, S.; Carr, C. M.; Delcourt, D.; Glassmeier, K. -H.; Grande, M.; Hirahara, M.; Huovelin, J.; Korablev, O.; Kojima, H.; Lichtenegger, H.; Livi, S.; Matsuoka, A.; Moissl, R.; Moncuquet, M.; Muinonen, K.; Quemerais, E.; Saito, Y.; Yagitani, S.; Yoshikawa, I.; Wahlund, J. -E. (2020)
    The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.
  • Osmane, Adnane; Dimmock, Andrew P.; Pulkkinen, Tuija I. (2019)
    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.
  • Grandin, Maxime; Palmroth, Minna; Whipps, Graeme; Kalliokoski, Milla; Ferrier, Mark; Paxton, Larry J.; Mlynczak, Martin G.; Hilska, Jukka; Holmseth, Knut; Vinorum, Kjetil; Whenman, Barry (2021)
    Recently, citizen scientist photographs led to the discovery of a new auroral form called "the dune aurora" which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. This study investigates a large-scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1,500 km for at least 4 h. Spacecraft observations indicate that the dunes are associated with particle precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west-southwest direction at about 200 m s(-1), presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least-known region of near-Earth space at altitudes near 100 km.
  • Palmroth, Minna; Grandin, Maxime; Sarris, Theodoros E.; Doornbos, Eelco; Tourgaidis, Stelios; Aikio, Anita; Buchert, Stephan; Clilverd, Mark A.; Dandouras, Iannis; Heelis, Roderick; Hoffmann, Alex; Ivchenko, Nickolay; Kervalishvili, Guram; Knudsen, David J.; Kotova, Anna; Liu, Han-Li; Malaspina, David M.; March, Gunther; Marchaudon, Aurélie; Marghitu, Octav; Matsuo, Tomoko; Miloch, Wojciech J.; Moretto-Jørgensen, Therese; Mpaloukidis, Dimitris; Olsen, Nils; Papadakis, Konstantinos; Pfaff, Robert; Pirnaris, Panagiotis; Siemes, Christian; Stolle, Claudia; Suni, Jonas; van den Ijssel, Jose; Verronen, Pekka T; Visser, Pieter; Yamauchi, Masatoshi (2021)
    The lower-thermosphere-ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.
  • Kilpua, E. K. J.; Hietala, H.; Koskinen, H. E. J.; Fontaine, D.; Turc, L. (2013)
  • Palmroth, Minna; Raptis, Savvas; Suni, Jonas; Karlsson, Tomas; Turc, Lucile; Johlander, Andreas; Ganse, Urs; Pfau-Kempf, Yann; Blanco-Cano, Xochitl; Akhavan-Tafti, Mojtaba; Battarbee, Markus; Dubart, Maxime; Grandin, Maxime; Tarvus, Vertti; Osmane, Adnane (2021)
    Magnetosheath jets are regions of high dynamic pressure, which can traverse from the bow shock towards the magnetopause. Recent modelling efforts, limited to a single jet and a single set of upstream conditions, have provided the first estimations about how the jet parameters behave as a function of position within the magnetosheath. Here we expand the earlier results by doing the first statistical investigation of the jet dimensions and parameters as a function of their lifetime within the magnetosheath. To verify the simulation behaviour, we first identify jets from Magnetosphere Multiscale (MMS) spacecraft data (6142 in total) and confirm the Vlasiator jet general behaviour using statistics of 924 simulated individual jets. We find that the jets in the simulation are in quantitative agreement with the observations, confirming earlier findings related to jets using Vlasiator. The jet density, dynamic pressure, and magnetic field intensity show a sharp jump at the bow shock, which decreases towards the magnetopause. The jets appear compressive and cooler than the magnetosheath at the bow shock, while during their propagation towards the magnetopause they thermalise. Further, the shape of the jets flatten as they progress through the magnetosheath. They are able to maintain their flow velocity and direction within the magnetosheath flow, and they end up preferentially to the side of the magnetosheath behind the quasi-parallel shock. Finally, we find that Vlasiator jets during low solar wind Alfven Mach number M-A are shorter in duration, smaller in their extent, and weaker in terms of dynamic pressure and magnetic field intensity as compared to the jets during high M-A.
  • Kilpua, Emilia K. J.; Good, Simon W.; Palmerio, Erika; Asvestari, Eleanna; Lumme, Erkka; Ala-Lahti, Matti; Kalliokoski, Milla M. H.; Morosan, Diana E.; Pomoell, Jens; Price, Daniel J.; Magdalenić, Jasmina; Poedts, Stefaan; Futaana, Yoshifumi (2019)
    We report a detailed analysis of interplanetary flux ropes observed at Venus and subsequently at Earth's Lagrange L1 point between June 15 and 17, 2012. The observation points were separated by about 0.28 AU in radial distance and 5 degrees in heliographic longitude at this time. The flux ropes were associated with three coronal mass ejections (CMEs) that erupted from the Sun on June 12-14, 2012 (SOL2012-06-12, SOL2012-06-13, and SOL2012-06-14). We examine the CME-CME interactions using in-situ observations from the almost radially aligned spacecraft at Venus and Earth, as well as using heliospheric modeling and imagery. The June 14 CME reached the June 13 CME near the orbit of Venus and significant interaction occurred before they both reached Earth. The shock driven by the June 14 CME propagated through the June 13 CME and the two CMEs coalesced, creating the signatures of one large, coherent flux rope at L1. We discuss the origin of the strong interplanetary magnetic fields related to this sequence of events, the complexity of interpreting solar wind observations in the case of multiple interacting CMEs, and the coherence of the flux ropes at different observation points.
  • Palmerio, Erika; Scolini, Camilla; Barnes, David; Magdalenic, Jasmina; West, Matthew J.; Zhukov, Andrei N.; Rodriguez, Luciano; Mierla, Marilena; Good, Simon W.; Morosan, Diana E.; Kilpua, Emilia K. J.; Pomoell, Jens; Poedts, Stefaan (2019)
    We analyze in this work the propagation and geoeffectiveness of four successive coronal mass ejections (CMEs) that erupted from the Sun during 2013 May 21-23 and were detected in interplanetary space by the Wind and/or STEREO-A spacecraft. All these CMEs featured critical aspects for understanding so-called "problem space weather storms" at Earth. In the first three events a limb CMEs resulted in moderately geoeffective in situ structures at their target location in terms of the disturbance storm time (Dst) index (either measured or estimated). The fourth CME, which also caused a moderate geomagnetic response, erupted from close to the disk center as seen from Earth, but it was not visible in coronagraph images from the spacecraft along the Sun-Earth line and appeared narrow and faint from off-angle viewpoints. Making the correct connection between CMEs at the Sun and their in situ counterparts is often difficult for problem storms. We investigate these four CMEs using multiwavelength and multipoint remote-sensing observations (extreme ultraviolet, white light, and radio), aided by 3D heliospheric modeling, in order to follow their propagation in the corona and in interplanetary space and to assess their impact at 1 au. Finally, we emphasize the difficulties in forecasting moderate space weather effects that are provoked by problematic and ambiguous events and the importance of multispacecraft data for observing and modeling problem storms.
  • Davies, Emma E.; Forsyth, Robert J.; Good, Simon W.; Kilpua, Emilia K. J. (2020)
    We present observations of the same magnetic cloud made near Earth by the Advance Composition Explorer (ACE), Wind, and the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission comprising the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and THEMIS C spacecraft, and later by Juno at a distance of 1.2 AU. The spacecraft were close to radial alignment throughout the event, with a longitudinal separation of 3.6 degrees between Juno and the spacecraft near Earth. The magnetic cloud likely originated from a filament eruption on 22 October 2011 at 00:05 UT, and caused a strong geomagnetic storm at Earth commencing on 24 October. Observations of the magnetic cloud at each spacecraft have been analysed using minimum variance analysis and two flux rope fitting models, Lundquist and Gold-Hoyle, to give the orientation of the flux rope axis. We explore the effect different trailing edge boundaries have on the results of each analysis method, and find a clear difference between the orientations of the flux rope axis at the near-Earth spacecraft and Juno, independent of the analysis method. The axial magnetic field strength and the radial width of the flux rope are calculated using both observations and fitting parameters and their relationship with heliocentric distance is investigated. Differences in results between the near-Earth spacecraft and Juno are attributed not only to the radial separation, but to the small longitudinal separation which resulted in a surprisingly large difference in the in situ observations between the spacecraft. This case study demonstrates the utility of Juno cruise data as a new opportunity to study magnetic clouds beyond 1 AU, and the need for caution in future radial alignment studies.
  • Kilpua, E. K. J.; Isavnin, A.; Vourlidas, A.; Koskinen, H. E. J.; Rodriguez, L. (2013)
  • Kilpua, E. K. J.; Turner, D. L.; Jaynes, A.; Hietala, H.; Koskinen, H. E. J.; Osmane, A.; Palmroth, M.; Pulkkinen, T. I.; Vainio, R.; Baker, D.; Claudepierre, S. (2019)
    We study the response of the outer Van Allen radiation belt during an intense magnetic storm on 15-22 February 2014. Four interplanetary coronal mass ejections (ICMEs) arrived at Earth, of which the three last ones were interacting. Using data from the Van Allen Probes, we report the first detailed investigation of electron fluxes from source (tens of kiloelectron volts) to core (megaelectron volts) energies and possible loss and acceleration mechanisms as a response to substructures (shock, sheath and ejecta, and regions of shock-compressed ejecta) in multiple interacting ICMEs. After an initial enhancement induced by a shock compression of the magnetosphere, core fluxes strongly depleted and stayed low for 4 days. This sustained depletion can be related to a sequence of ICME substructures and their conditions that influenced the Earth's magnetosphere. In particular, the main depletions occurred during a high-dynamic pressure sheath and shock-compressed southward ejecta fields. These structures compressed/eroded the magnetopause close to geostationary orbit and induced intense and diverse wave activity in the inner magnetosphere (ULF Pc5, electromagnetic ion cyclotron, and hiss) facilitating both effective magnetopause shadowing and precipitation losses. Seed and source electrons in turn experienced stronger variations throughout the studied interval. The core fluxes recovered during the last ICME that made a glancing blow to Earth. This period was characterized by a concurrent lack of losses and sustained acceleration by chorus and Pc5 waves. Our study highlights that the seemingly complex behavior of the outer belt during interacting ICMEs can be understood by the knowledge of electron dynamics during different substructures.
  • Palmerio, Erika; Kilpua, Emilia K. J.; Savani, Neel P. (2016)
    Planar magnetic structures (PMSs) are periods in the solar wind during which interplanetary magnetic field vectors are nearly parallel to a single plane. One of the specific regions where PMSs have been reported are coronal mass ejection (CME)-driven sheaths. We use here an automated method to identify PMSs in 95 CME sheath regions observed in situ by the Wind and ACE spacecraft between 1997 and 2015. The occurrence and location of the PMSs are related to various shock, sheath, and CME properties. We find that PMSs are ubiquitous in CME sheaths; 85% of the studied sheath regions had PMSs with the mean duration of 6 h. In about one-third of the cases the magnetic field vectors followed a single PMS plane that covered a significant part (at least 67%) of the sheath region. Our analysis gives strong support for two suggested PMS formation mechanisms: the amplification and alignment of solar wind discontinuities near the CME-driven shock and the draping of the magnetic field lines around the CME ejecta. For example, we found that the shock and PMS plane normals generally coincided for the events where the PMSs occurred near the shock (68% of the PMS plane normals near the shock were separated by less than 20 degrees from the shock normal), while deviations were clearly larger when PMSs occurred close to the ejecta leading edge. In addition, PMSs near the shock were generally associated with lower upstream plasma beta than the cases where PMSs occurred near the leading edge of the CME. We also demonstrate that the planar parts of the sheath contain a higher amount of strong southward magnetic field than the non-planar parts, suggesting that planar sheaths are more likely to drive magnetospheric activity.
  • Takahashi, Kazue; Turc, Lucile; Kilpua, Emilia; Takahashi, Naoko; Dimmock, Andrew P.; Kajdic, Primoz; Palmroth, Minna; Pfau-Kempf, Yann; Souček, Jan; Motoba, Tetsuo; Hartinger, Michael D.; Artemyev, Anton; Singer, Howard; Ganse, Urs; Battarbee, Markus (2021)
    We have examined the properties of ultralow-frequency (ULF) waves in space (the ion foreshock, magnetosheath, and magnetosphere) and at dayside magnetometer stations (L = 1.6-6.5) during Earth's encounter with a magnetic cloud in the solar wind, which is characterized by magnetic fields with large magnitudes (similar to 14 nT) and small cone angles (similar to 30 degrees). In the foreshock, waves were excited at similar to 90 m Hz as expected from theory, but there were oscillations at other frequencies as well. Oscillations near 90 mHz were detected at the other locations in space, but they were not in general the most dominant oscillations. On the ground, pulsations in the approximate Pc2-Pc4 band (5 mHz-120 mHz) were continuously detected at all stations, with no outstanding spectral peaks near 90 mHz in the H component except at stations where the frequency of the third harmonic of standing Alfven waves had this frequency. The fundamental toroidal wave frequency was below 90 mHz at all stations. In the D component spectra, a minor spectral peak is found near 90 mHz at stations located at L <3, and the power dropped abruptly above this frequency. Magnetospheric compressional wave power was much weaker on the nightside. A hybrid-Vlasov simulation indicates that foreshock ULF waves have short spatial scale lengths and waves transmitted into the magnetosphere are strongly attenuated away from noon.
  • Alho, Markku; Jarvinen, Riku; Wedlund, Cyril Simon; Nilsson, Hans; Kallio, Esa; Pulkkinen, Tuija (2021)
    Despite the long escort by the ESA Rosetta mission, direct observations of a fully developed bow shock around 67P/Churyumov-Gerasimenko have not been reported. Expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the ESA Rosetta Plasma Consortium Ion Composition Analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. Using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67P, and varied interplanetary magnetic field (IMF) clock angles, we model the evolution of the large-scale plasma environment. We find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to 18 000 km approaching perihelion. We find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and IMF configuration. Asymmetric outgassing along with IMF clock angle is found to have a strong effect on the location of the spectral features, while the IMF clock angle causes no significant effect on the bow shock standoff distance. These dependences further complicate the interpretation of the ion observations made by Rosetta. Our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet's activity is comparable to that of 67P, and the solar wind parameters are known.
  • Good, S.W.; Kilpua, E.K.J.; LaMoury, A.T.; Forsyth, R.J.; Eastwood, J.P.; Möstl, C. (2019)
    Abstract Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation, and the evolution of ICME magnetic field structure during propagation, are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east-west direction with heliocentric distance.
  • Palmroth, M.; Laitinen, T. V.; Anekallu, C. R.; Pulkkinen, T. I.; Dunlop, M.; Lucek, E. A.; Dandouras, I. (2011)
  • Dimmock, A. P.; Osmane, A.; Pulkkinen, T. I.; Nykyri, K.; Kilpua, E. (2017)
    The magnetosheath contains an array of waves, instabilities, and nonlinear magnetic structures which modify global plasma properties by means of various wave-particle interactions. The present work demonstrates that ion-scale magnetic field structures (similar to 0.2-0.5 Hz) observed in the dayside magnetosheath are statistically correlated to ion temperature changes on orders 10-20% of the background value. In addition, our statistical analysis implies that larger temperature changes are in equipartition to larger amplitude magnetic structures. This effect was more pronounced behind the quasi-parallel bow shock and during faster solar wind speeds. The study of two separate intervals suggests that this effect can result from both local and external drivers. This manuscript presents two separate case studies, one from using THEMIS (Time History of Events and Macroscale Interactions during Substorms) data and another from Magnetospheric Multiscale; these measurements are then supported by extensive THEMIS statistical observations. These results could partly explain the 10-20% dawn-favored asymmetry of the magnetosheath ion temperature seed population and contribute to the dawn-favored asymmetry of cold component ions in the cold dense plasma sheet.
  • Turner, D. L.; Kilpua, E. K. J.; Hietala, H.; Claudepierre, S. G.; O'Brien, T. P.; Fennell, J. F.; Blake, J. B.; Jaynes, A. N.; Kanekal, S.; Baker, D. N.; Spence, H. E.; Ripoll, J.-F.; Reeves, G. D. (2019)
    A statistical study was conducted of Earth's radiation belt electron response to geomagnetic storms using NASA's Van Allen Probes mission. Data for electrons with energies ranging from 30 keV to 6.3 MeV were included and examined as a function of L-shell, energy, and epoch time during 110 storms with SYM-H 1 MeV also revealed a marked increase in likelihood of a depletion at all L-shells through the outer belt (3.5 1-MeV electrons throughout the outer belt, while storms driven by full CMEs and stream interaction regions are most likely to produce an enhancement of MeV electrons at lower (L <similar to 5) and higher (L > similar to 4.5) L-shells, respectively. CME sheaths intriguingly result in a distinct enhancement of similar to 1-MeV electrons around L similar to 5.5, and on average, CME sheaths and stream interaction regions result in double outer belt structures.