The passage of an interplanetary shock caused a sudden compression of the magnetosphere between 0... more The passage of an interplanetary shock caused a sudden compression of the magnetosphere between 0900 UT and 0915 UT on 24 August 2005. An estimate of the shock normal from solar wind data obtained by Geotail upstream of the bow shock indicates symmetric compression with respect to the noon-midnight meridian. Compression-related disturbances of the magnetic and electric field and plasma motion were observed by Double Star Program (DSP) Tan Ce 1 (TC1) and Tan Ce 2 (TC2) in the inner magnetosphere and by the Cluster spacecraft in the dawnside plasma sheet. DSP/TC1 and TC2 observations suggest that the disturbances in the inner magnetosphere are propagating from the dayside magnetopause. Cluster S/C 4 observations indicate that the front normal of the disturbances in the dawnside plasma sheet is f $ 180°at 0902:50 UT and f = 107°at 0904:34 UT, where f is the longitude in GSM coordinates, if we assume that the measured electric field is on the front plane and the normal lies on the X-Y plane. The timing analysis applied to magnetic field data from the four Cluster spacecraft independently gives a front normal, which is calculated to be f = 131°at about 0904:20 UT. Shock-associated magnetic and electric field disturbances propagating from both the dayside and flank magnetopauses are detected in the plasma sheet; the latter makes the dominant contribution. Substorms are, however, not triggered at the passage of the disturbances.
TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Ca... more TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the Exp Astron (2009) 23:893-946 895 other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere.
ABSTRACT The Charge-Energy-Mass Spectrometer (CHEMS), one of three sensors comprising the MIMI in... more ABSTRACT The Charge-Energy-Mass Spectrometer (CHEMS), one of three sensors comprising the MIMI investigation on Cassini, measures the mass and charge state of ions in the energy per charge range 3--220 keV/e. During Titan-5, Cassini's fifth close flyby of Titan on day 106, 2005, CHEMS observed an anisotropic flux of heavy ions during a 10-minute period beginning about 1915 UT, 3 minutes after closest approach. The measured ion masses ranged from 14--30 amu. Their energy spectrum exhibited a sharp cutoff above 12 keV. These ions are presumably pickup ions from Titan. We will discuss their composition, anisotropy, and energy spectrum in terms of acceleration by the corotation electric field.
1] This paper reports Cluster high-altitude observations above the acceleration region of a typic... more 1] This paper reports Cluster high-altitude observations above the acceleration region of a typical monopolar electric field event at the plasma sheet boundary. The observations reveal both characteristics of waves and signatures of electrostatic acceleration. The observations can be interpreted in terms of low-frequency transverse magnetic waves on the auroral interface. A reconstruction of the spatial structure across the interface, effectively correcting for the slow oscillations of the interface, allows a proper determination of the electric potential and of the upward and downward currents. Because of the long wave period, the auroral system can be understood in terms of a quasi-electrostatic model. In this model, the precipitating plasma sheet particles induce a perpendicular heating of cold ionospheric H + and O + ions. As these ions escape from the ionosphere, their perpendicular motion is converted into parallel motion in the divergent geomagnetic field as a result of the conservation of magnetic moment. These ions acquire an additional parallel energy through acceleration by the magnetic-field-aligned electric field in the auroral acceleration region. They also may gain substantial perpendicular energy due to the perpendicular electric field, as theẼ ×B drift increases with altitude. Both types of acceleration are typical electrostatic phenomena. Citation: De Keyser, J., R. Maggiolo, M. Echim, and I. Dandouras (2011), Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling,
SWEA, the solar wind electron analyzers that are part of the IMPACT in situ investigation for the... more SWEA, the solar wind electron analyzers that are part of the IMPACT in situ investigation for the STEREO mission, are described. They are identical on each of the two spacecraft. Both are designed to provide detailed measurements of interplanetary electron distribution functions in the energy range 1∼3000 eV and in a 120°×360°solid angle sector. This energy range covers the core or thermal solar wind plasma electrons, and the suprathermal halo electrons including the field-aligned heat flux or strahl used to diagnose the interplanetary magnetic field topology. The potential of each analyzer will be varied in order to maintain their energy resolution for spacecraft potentials comparable to the solar wind thermal electron energies. Calibrations have been performed that show the performance of the devices are in good agreement with calculations and will allow precise diagnostics of all of the interplanetary electron populations at the two STEREO spacecraft locations.
We present observations of E <= 40 keV/e ions measured by the Cluster Ion Spectrometry experim... more We present observations of E <= 40 keV/e ions measured by the Cluster Ion Spectrometry experiment at ~ 0.5 RE upstream of the bow shock. The ions were simultaneously observed by three of the spacecraft. The proton and helium ion distributions are analyzed at 4-second time resolution. These ion distributions are observed in association with low-frequency waves having substantial amplitudes
Previous work has shown that solar wind suprathermal electrons can display a number of features i... more Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counterstreaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counterstreaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March -December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15-20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate > 35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunwarddirected fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs. isotropic suprathermal population (typically above 70 eV); and (3) the "strahl", an intense beam of suprathermal electrons aligned to the magnetic field and directed outward from the Sun; it carries a substantial heat flux away from the solar corona. Solar wind electron spectra near 1 AU are characterized by a clear spectral breakpoint around 70 eV that separates the halo and strahl from the thermal electrons.
ABSTRACT Electric currents flowing through geospace support a highly nondipolar magnetic field to... more ABSTRACT Electric currents flowing through geospace support a highly nondipolar magnetic field topology, and their time-varying dynamics change particle drift paths and create a nonlinear feedback on the currents themselves. A number of current systems exist in the magnetosphere, most commonly the dayside magnetopause Chapman-Ferraro currents, high latitude &quot;region 1&quot; field-aligned Birkeland currents, lower-latitude &quot;region 2&quot; field-aligned currents connected to the partial ring current, magnetotail currents, and the symmetric ring current. In the near-Earth nightside, however, several of these current systems flow in close proximity to each other and it is very difficult to identify a local measurement as belonging to a specific system. Such identification is important, however, because how the current closes and how these loops change in space and time governs the magnetic topology of the magnetosphere and therefore controls the physical processes of geospace. Furthermore, many methods exist for identifying the regions of near-Earth space carrying each type of current. This study presents a robust collection of these definitions of current systems in geospace, particularly in the near-Earth nightside magnetosphere, as viewed from a variety of observational and computational analysis techniques. The influence of definitional choice on the resulting interpretation of physical processes governing geospace dynamics is presented and discussed.
Hot flow anomalies (HFAs) are studied using observations of the FGM 5 magnetometer and the CIS pl... more Hot flow anomalies (HFAs) are studied using observations of the FGM 5 magnetometer and the CIS plasma detector aboard the four Cluster spacecraft. Pre-6 viously we studied several specific features of tangential discontinuities on the basis 7 of Cluster measurements in February-April 2003 and discovered a new condition 8 for forming HFAs that is the solar wind speed is higher than the average. How-9 ever during the whole spring season of 2003, the solar wind speed was higher than 10 average. In this study we analyse HFAs detected in 2007, the year of solar cycle 11 minimum. Our earlier result was confirmed: the higher solar wind speed is a real 12 condition for HFA formation; furthermore this constraint is independent of Schwartz 13 et al.'s condition for HFA formation. AQ1 14 G. Facskó ( ), M. Tátrallyay, and G. Erdős
The bow shock and upstream solar wind are extremely dynamic. A portion of the solar wind is refle... more The bow shock and upstream solar wind are extremely dynamic. A portion of the solar wind is reflected off the bow shock and travel back upstream. Magnetosheath particles also travel upstream on interplanetary magnetic field that connects to the bow shock. These backstreaming particles disturb the solar wind, excite instabilities and produce complex structures. We report novel observations of a class of ion density depletions that have durations of ~20s but as short as 8s. They are ubiquitous and seen out to Cluster apogee distance of ~19 RE. The temperature in the ion holes is a few million oK and the density can fall below the instrument detection threshold (~0.01/cc). The shapes are symmetric with both edges slightly elevated or highly asymmetric with only one edge elevated. The ion holes are accompanied by similarly shaped magnetic holes whose interior intensity is considerably reduced and fluctuating but at the edges highly enhanced and shock-like as in short, large-amplitude magnetic structures (SLAMS). 3D analysis shows the ion holes have dimensions of about a gyroradius of 4 keV protons and convecting with the solar wind. The electric fields at the edges are bipolar and the accompanying magnetic field undergoes either rotation or compression. These ion holes may be a previously unresolvable, early-development stage of the much more rare hot diamagnetic cavity structures or hot flow anomalies. The most likely theoretical explanations for these ion holes is that they are solitary Alfvenic structures produced by the nonlinear steepening of Alfven waves and evolving into coherent structures.
Journal of Geophysical Research: Space Physics, 2013
ABSTRACT We investigate magnetopause energy conversion in a large statistical data set utilizing ... more ABSTRACT We investigate magnetopause energy conversion in a large statistical data set utilizing Cluster spacecraft observations. We have compiled a database of about 4000 magnetopause crossings from Cluster spacecraft 1 (SC1) measurements during years 2001 - 2008. We have estimated the local energy conversion across the magnetopause for these crossings using Generic Residue Analysis (GRA) and analyzed the spatial distribution of load and generator regions during dayside and lobe reconnection as a function of the IMF magnitude and solar wind dynamic pressure. We found a scatter of the load and the generator regions on the magnetopause surface. Categorizing the crossings into equatorward or tailward of the cusp organizes the load and generators on the surface. During dayside reconnection, equatorward (tailward) of the cusp indicates more load (generator) than generator and is in agreement with theory. During lobe reconnection, we find that a load region dominates both equatorward and tailward of the cusp. We compare the statistics with GUMICS-4 global magnetohydrodynamic simulation results and find that there is a reasonable agreement, although disagreements are also found especially during lobe reconnection. We also investigate the influence of IMF magnitude on the load and generator locations and suggest that the spatial mixing of load and generators is due to rapid movement of the magnetopause surface which in turns moves the locations where load and generator processes appear. The solar wind dynamic pressure controls the magnitude of energy conversion across the magnetopause, and higher dynamic pressures lead to more energy conversion and vice versa.
The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-win... more The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-wind properties in the ecliptic since their longitudinal separation increases with time. We derive the characteristic temporal variations at ∼ 1 AU between two different plasma parcels ejected from the same solar source by excluding the spatial variations from our datasets. As part of the onboard IMPACT instrument suite, the SWEA electron experiment provides the solar-wind electron core density at two different heliospheric vantage points. We analyze these density datasets between March and August 2007 and find typical solar minimum conditions. After adjusting for the theoretical time lag between the two spacecraft, we compare the two density datasets. We find that their correlation decreases
We analyze Wind, ACE and STEREO (A and B) plasma and magnetic field data in the vicinity of the h... more We analyze Wind, ACE and STEREO (A and B) plasma and magnetic field data in the vicinity of the heliospheric current sheet (HCS) crossed by all spacecraft between 22:15 UT on March 31 and 01:25 UT on April 1, 2007; corresponding to its observation at ST-A and ST-B which were separated by over 1800 R E (or over 1200 R E across the Sun-Earth line). Although only Wind and ACE provided good ion flow data in accord with a solar wind magnetic reconnection exhaust at the HCS, the magnetic field bifurcation typical of such exhausts was clearly observed at all spacecraft. They also all observed unambiguous strahl mixing within the exhaust, consistent with the sunward flow deflection observed at Wind and ACE and thus with the formation of closed magnetic field lines within the exhaust with both ends attached to the Sun. The strong dawnward flow deflection in the exhaust is consistent with the exhaust and X-line orientations obtained from minimum variance analysis at each spacecraft so that the X-line is almost along the GSE Z-axis and duskward of all the spacecraft. The observation of strahl mixing in extended and intermittent layers outside the exhaust by ST-A and B is consistent with the formation of electron separatrix layers surrounding the exhaust. This event also provides further evidence that balanced parallel and anti-parallel suprathermal electron fluxes are not a necessary condition for identification of closed field lines in the solar wind. In the present case the origin of the imbalance simply is the mixing of strahls of substantially different strengths from a different solar source each side of the HCS. The inferred exhaust orientations and distances of each spacecraft relative to the X-line show that the exhaust was likely non-planar, following the Parker spiral orientation. Finally, the separatrix layers and exhausts properties at each spacecraft suggest that the magnetic reconnection X-line location and/or reconnection rate were variable in both space and time at such large scales.
The Ion And Neutral Camera (INCA) sensor of the Cassini Magnetospheric Imaging Instrument (MIMI) ... more The Ion And Neutral Camera (INCA) sensor of the Cassini Magnetospheric Imaging Instrument (MIMI) may be configured either as an energetic neutral atom (ENA) camera, or as a sensitive energetic ion sensor. During the distant approach of Cassini to Saturn, the ENA emission from Saturn is too weak to take advantage of the ENA imaging capability of INCA, and so it was configured to measure 10-200 keV/nucleon energetic ions in the solar wind. INCA is easily the most sensitive instrument in this energy range to have measured heliospheric energetic ions in the region between Jupiter and Saturn. The measurements are dominated by ions accelerated at interplanetary shocks, as both coronal mass ejections and corotating interaction regions pass the Cassini spacecraft. The angular distributions of these ions have not been fully charaterized over most of this region, as Cassini remained typically 3-axis oriented and INCA can measure only over a 90o x 120o field of view. From the beginning of 2004...
1] Cluster CIS ion spectrograms measured during the period of the recent solar minimum between . ... more 1] Cluster CIS ion spectrograms measured during the period of the recent solar minimum between . We demonstrate how the background counts produced by energetic particles of the radiation belts in Cluster CIS and Double Star HIA instruments can be interpreted to obtain the locations of the boundaries of the outer and inner belts. The obtained L-MLT distribution of boundaries reflects the general structure of the radiation belts. Closer examination of the time-dependent L locations of the boundaries reveals several dips to lower L-shells (from L = 6 to L = 4) in the outer boundary location. The importance of the solar wind pressure increases for the Earthward shift of the outer boundary of the outer belt is discussed. The location and thickness of the slot region are studied using the determined inner boundaries of the outer belt and the outer boundaries of the inner belt. It was found that during intervals of low activity in the solar wind parameters, the slot region widens, which is consistent with weaker inward radial diffusion, and also with weaker local acceleration that can occur only at higher L-shells outside the plasmasphere. We conclude that boundaries of radiation belts determined from background measurements on the instruments with energy ranges that do not cover the radiation belts' energies provide valuable additional information that is useful for radiation belts' model development and validation. Citation: Ganushkina, N. Y., I. Dandouras, Y. Y. Shprits, and J. Cao (2011), Locations of boundaries of outer and inner radiation belts as observed by Cluster and Double Star,
1] How the solar wind affects the location of the magnetopause has been widely studied and excell... more 1] How the solar wind affects the location of the magnetopause has been widely studied and excellent models of the magnetopause based on in situ observations in the solar wind and at the magnetopause have been established, while the careful insight into the responses of the magnetopause to the variations in the solar wind can still provide us some new information about the processes in space plasmas. The short distance from Cluster to TC-1 on 9 March 2004, between 06:10 and 08:10 UT, gives us a good opportunity to precisely monitor the responses of the magnetopause to the variations in the solar wind. On the basis of the combined observations between Cluster, TC-1, and SuperDARN we analyze the magnetopause crossings associated with magnetopause motion or magnetic reconnection when the solar wind conditions have a series of variations. New results about the time delays for the propagation from the solar wind monitor to the magnetopause of the interplanetary magnetic fields (IMF) and of the solar wind dynamic pressure, respectively, and the intrinsic time for reconnection onset at the magnetopause are obtained. The most important feature of the event is that the dynamic pressure and the IMF in the solar wind do not arrive at the magnetopause at the same time, which will direct us to find out how the variation in the solar wind dynamic pressure is transported from the bow shock to the magnetopause. Another significant feature is that this event presents a shorter intrinsic time, ∼2 min, for reconnection onset at the dayside magnetopause than that given by the previous work of Le et al. (2011), Magnetopause response to variations in the solar wind: Conjunction observations between Cluster, TC-1, and SuperDARN,
1] We present a small statistical data set, where we investigate energy conversion at the magneto... more 1] We present a small statistical data set, where we investigate energy conversion at the magnetopause using Cluster measurements of magnetopause crossings. The Cluster observations of magnetic field, plasma velocity, current density and magnetopause orientation are needed to infer the energy conversion at the magnetopause. These parameters can be inferred either from accurate multispacecraft methods, or by using single-spacecraft methods. Our final aim is a large statistical study, for which only single-spacecraft methods can be applied. The Cluster mission provides an opportunity to examine and validate single-spacecraft methods against the multispacecraft methods. For single-spacecraft methods, we use the Generic Residue Analysis (GRA) and a standard one-dimensional current density method using magnetic field measurements. For multispacecraft methods, we use triangulation (Constant Velocity Approach -CVA) and the curlometer technique. We find that in some cases the single-spacecraft methods yield a different sign for the energy conversion than compared to the multispacecraft methods. These sign ambiguities arise from the orientation of the magnetopause, choosing the interval to be analyzed, large normal current and time offset of the current density inferred from the two methods. By using the Finnish Meteorological Institute global MHD simulation GUMICS-4, we are able to determine which sign is likely to be correct, introducing an opportunity to correct the ambiguous energy conversion values. After correcting the few ambiguous cases, we find that the energy conversion estimated from single-spacecraft methods is generally lower by 70% compared to the multispacecraft methods.
Several hot flow anomaly (HFA) like events were observed by STEREO magnetometer (MAG) and solar w... more Several hot flow anomaly (HFA) like events were observed by STEREO magnetometer (MAG) and solar wind thermal proton (PLASTIC) and electron (SWEA) instruments during the Earth orbit phase of STEREO B in February-March, 2007. The magnetic signature of the tangential discontinuities (TDs) was observed but the resolution of PLASTIC is not sufficient to identify the events without any doubt. The events are identified using the simultaneous measurements of the Cluster fluxgate magnetometer (FGM), ion (CIS/HIA) and resonance sounder (WHISPER) instruments. No HFA events were observed so far from the Earth before and these events are in the very late phase of HFA development. The comparison of these events using data acquired by Cluster and STEREO is a unique opportunity for studying the HFA characteristics far from its generation region, its turbulent features and its spatial-temporal development.
The passage of an interplanetary shock caused a sudden compression of the magnetosphere between 0... more The passage of an interplanetary shock caused a sudden compression of the magnetosphere between 0900 UT and 0915 UT on 24 August 2005. An estimate of the shock normal from solar wind data obtained by Geotail upstream of the bow shock indicates symmetric compression with respect to the noon-midnight meridian. Compression-related disturbances of the magnetic and electric field and plasma motion were observed by Double Star Program (DSP) Tan Ce 1 (TC1) and Tan Ce 2 (TC2) in the inner magnetosphere and by the Cluster spacecraft in the dawnside plasma sheet. DSP/TC1 and TC2 observations suggest that the disturbances in the inner magnetosphere are propagating from the dayside magnetopause. Cluster S/C 4 observations indicate that the front normal of the disturbances in the dawnside plasma sheet is f $ 180°at 0902:50 UT and f = 107°at 0904:34 UT, where f is the longitude in GSM coordinates, if we assume that the measured electric field is on the front plane and the normal lies on the X-Y plane. The timing analysis applied to magnetic field data from the four Cluster spacecraft independently gives a front normal, which is calculated to be f = 131°at about 0904:20 UT. Shock-associated magnetic and electric field disturbances propagating from both the dayside and flank magnetopauses are detected in the plasma sheet; the latter makes the dominant contribution. Substorms are, however, not triggered at the passage of the disturbances.
TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Ca... more TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the Exp Astron (2009) 23:893-946 895 other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere.
ABSTRACT The Charge-Energy-Mass Spectrometer (CHEMS), one of three sensors comprising the MIMI in... more ABSTRACT The Charge-Energy-Mass Spectrometer (CHEMS), one of three sensors comprising the MIMI investigation on Cassini, measures the mass and charge state of ions in the energy per charge range 3--220 keV/e. During Titan-5, Cassini&#39;s fifth close flyby of Titan on day 106, 2005, CHEMS observed an anisotropic flux of heavy ions during a 10-minute period beginning about 1915 UT, 3 minutes after closest approach. The measured ion masses ranged from 14--30 amu. Their energy spectrum exhibited a sharp cutoff above 12 keV. These ions are presumably pickup ions from Titan. We will discuss their composition, anisotropy, and energy spectrum in terms of acceleration by the corotation electric field.
1] This paper reports Cluster high-altitude observations above the acceleration region of a typic... more 1] This paper reports Cluster high-altitude observations above the acceleration region of a typical monopolar electric field event at the plasma sheet boundary. The observations reveal both characteristics of waves and signatures of electrostatic acceleration. The observations can be interpreted in terms of low-frequency transverse magnetic waves on the auroral interface. A reconstruction of the spatial structure across the interface, effectively correcting for the slow oscillations of the interface, allows a proper determination of the electric potential and of the upward and downward currents. Because of the long wave period, the auroral system can be understood in terms of a quasi-electrostatic model. In this model, the precipitating plasma sheet particles induce a perpendicular heating of cold ionospheric H + and O + ions. As these ions escape from the ionosphere, their perpendicular motion is converted into parallel motion in the divergent geomagnetic field as a result of the conservation of magnetic moment. These ions acquire an additional parallel energy through acceleration by the magnetic-field-aligned electric field in the auroral acceleration region. They also may gain substantial perpendicular energy due to the perpendicular electric field, as theẼ ×B drift increases with altitude. Both types of acceleration are typical electrostatic phenomena. Citation: De Keyser, J., R. Maggiolo, M. Echim, and I. Dandouras (2011), Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling,
SWEA, the solar wind electron analyzers that are part of the IMPACT in situ investigation for the... more SWEA, the solar wind electron analyzers that are part of the IMPACT in situ investigation for the STEREO mission, are described. They are identical on each of the two spacecraft. Both are designed to provide detailed measurements of interplanetary electron distribution functions in the energy range 1∼3000 eV and in a 120°×360°solid angle sector. This energy range covers the core or thermal solar wind plasma electrons, and the suprathermal halo electrons including the field-aligned heat flux or strahl used to diagnose the interplanetary magnetic field topology. The potential of each analyzer will be varied in order to maintain their energy resolution for spacecraft potentials comparable to the solar wind thermal electron energies. Calibrations have been performed that show the performance of the devices are in good agreement with calculations and will allow precise diagnostics of all of the interplanetary electron populations at the two STEREO spacecraft locations.
We present observations of E <= 40 keV/e ions measured by the Cluster Ion Spectrometry experim... more We present observations of E <= 40 keV/e ions measured by the Cluster Ion Spectrometry experiment at ~ 0.5 RE upstream of the bow shock. The ions were simultaneously observed by three of the spacecraft. The proton and helium ion distributions are analyzed at 4-second time resolution. These ion distributions are observed in association with low-frequency waves having substantial amplitudes
Previous work has shown that solar wind suprathermal electrons can display a number of features i... more Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counterstreaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counterstreaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March -December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15-20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate > 35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunwarddirected fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs. isotropic suprathermal population (typically above 70 eV); and (3) the "strahl", an intense beam of suprathermal electrons aligned to the magnetic field and directed outward from the Sun; it carries a substantial heat flux away from the solar corona. Solar wind electron spectra near 1 AU are characterized by a clear spectral breakpoint around 70 eV that separates the halo and strahl from the thermal electrons.
ABSTRACT Electric currents flowing through geospace support a highly nondipolar magnetic field to... more ABSTRACT Electric currents flowing through geospace support a highly nondipolar magnetic field topology, and their time-varying dynamics change particle drift paths and create a nonlinear feedback on the currents themselves. A number of current systems exist in the magnetosphere, most commonly the dayside magnetopause Chapman-Ferraro currents, high latitude &quot;region 1&quot; field-aligned Birkeland currents, lower-latitude &quot;region 2&quot; field-aligned currents connected to the partial ring current, magnetotail currents, and the symmetric ring current. In the near-Earth nightside, however, several of these current systems flow in close proximity to each other and it is very difficult to identify a local measurement as belonging to a specific system. Such identification is important, however, because how the current closes and how these loops change in space and time governs the magnetic topology of the magnetosphere and therefore controls the physical processes of geospace. Furthermore, many methods exist for identifying the regions of near-Earth space carrying each type of current. This study presents a robust collection of these definitions of current systems in geospace, particularly in the near-Earth nightside magnetosphere, as viewed from a variety of observational and computational analysis techniques. The influence of definitional choice on the resulting interpretation of physical processes governing geospace dynamics is presented and discussed.
Hot flow anomalies (HFAs) are studied using observations of the FGM 5 magnetometer and the CIS pl... more Hot flow anomalies (HFAs) are studied using observations of the FGM 5 magnetometer and the CIS plasma detector aboard the four Cluster spacecraft. Pre-6 viously we studied several specific features of tangential discontinuities on the basis 7 of Cluster measurements in February-April 2003 and discovered a new condition 8 for forming HFAs that is the solar wind speed is higher than the average. How-9 ever during the whole spring season of 2003, the solar wind speed was higher than 10 average. In this study we analyse HFAs detected in 2007, the year of solar cycle 11 minimum. Our earlier result was confirmed: the higher solar wind speed is a real 12 condition for HFA formation; furthermore this constraint is independent of Schwartz 13 et al.'s condition for HFA formation. AQ1 14 G. Facskó ( ), M. Tátrallyay, and G. Erdős
The bow shock and upstream solar wind are extremely dynamic. A portion of the solar wind is refle... more The bow shock and upstream solar wind are extremely dynamic. A portion of the solar wind is reflected off the bow shock and travel back upstream. Magnetosheath particles also travel upstream on interplanetary magnetic field that connects to the bow shock. These backstreaming particles disturb the solar wind, excite instabilities and produce complex structures. We report novel observations of a class of ion density depletions that have durations of ~20s but as short as 8s. They are ubiquitous and seen out to Cluster apogee distance of ~19 RE. The temperature in the ion holes is a few million oK and the density can fall below the instrument detection threshold (~0.01/cc). The shapes are symmetric with both edges slightly elevated or highly asymmetric with only one edge elevated. The ion holes are accompanied by similarly shaped magnetic holes whose interior intensity is considerably reduced and fluctuating but at the edges highly enhanced and shock-like as in short, large-amplitude magnetic structures (SLAMS). 3D analysis shows the ion holes have dimensions of about a gyroradius of 4 keV protons and convecting with the solar wind. The electric fields at the edges are bipolar and the accompanying magnetic field undergoes either rotation or compression. These ion holes may be a previously unresolvable, early-development stage of the much more rare hot diamagnetic cavity structures or hot flow anomalies. The most likely theoretical explanations for these ion holes is that they are solitary Alfvenic structures produced by the nonlinear steepening of Alfven waves and evolving into coherent structures.
Journal of Geophysical Research: Space Physics, 2013
ABSTRACT We investigate magnetopause energy conversion in a large statistical data set utilizing ... more ABSTRACT We investigate magnetopause energy conversion in a large statistical data set utilizing Cluster spacecraft observations. We have compiled a database of about 4000 magnetopause crossings from Cluster spacecraft 1 (SC1) measurements during years 2001 - 2008. We have estimated the local energy conversion across the magnetopause for these crossings using Generic Residue Analysis (GRA) and analyzed the spatial distribution of load and generator regions during dayside and lobe reconnection as a function of the IMF magnitude and solar wind dynamic pressure. We found a scatter of the load and the generator regions on the magnetopause surface. Categorizing the crossings into equatorward or tailward of the cusp organizes the load and generators on the surface. During dayside reconnection, equatorward (tailward) of the cusp indicates more load (generator) than generator and is in agreement with theory. During lobe reconnection, we find that a load region dominates both equatorward and tailward of the cusp. We compare the statistics with GUMICS-4 global magnetohydrodynamic simulation results and find that there is a reasonable agreement, although disagreements are also found especially during lobe reconnection. We also investigate the influence of IMF magnitude on the load and generator locations and suggest that the spatial mixing of load and generators is due to rapid movement of the magnetopause surface which in turns moves the locations where load and generator processes appear. The solar wind dynamic pressure controls the magnitude of energy conversion across the magnetopause, and higher dynamic pressures lead to more energy conversion and vice versa.
The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-win... more The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-wind properties in the ecliptic since their longitudinal separation increases with time. We derive the characteristic temporal variations at ∼ 1 AU between two different plasma parcels ejected from the same solar source by excluding the spatial variations from our datasets. As part of the onboard IMPACT instrument suite, the SWEA electron experiment provides the solar-wind electron core density at two different heliospheric vantage points. We analyze these density datasets between March and August 2007 and find typical solar minimum conditions. After adjusting for the theoretical time lag between the two spacecraft, we compare the two density datasets. We find that their correlation decreases
We analyze Wind, ACE and STEREO (A and B) plasma and magnetic field data in the vicinity of the h... more We analyze Wind, ACE and STEREO (A and B) plasma and magnetic field data in the vicinity of the heliospheric current sheet (HCS) crossed by all spacecraft between 22:15 UT on March 31 and 01:25 UT on April 1, 2007; corresponding to its observation at ST-A and ST-B which were separated by over 1800 R E (or over 1200 R E across the Sun-Earth line). Although only Wind and ACE provided good ion flow data in accord with a solar wind magnetic reconnection exhaust at the HCS, the magnetic field bifurcation typical of such exhausts was clearly observed at all spacecraft. They also all observed unambiguous strahl mixing within the exhaust, consistent with the sunward flow deflection observed at Wind and ACE and thus with the formation of closed magnetic field lines within the exhaust with both ends attached to the Sun. The strong dawnward flow deflection in the exhaust is consistent with the exhaust and X-line orientations obtained from minimum variance analysis at each spacecraft so that the X-line is almost along the GSE Z-axis and duskward of all the spacecraft. The observation of strahl mixing in extended and intermittent layers outside the exhaust by ST-A and B is consistent with the formation of electron separatrix layers surrounding the exhaust. This event also provides further evidence that balanced parallel and anti-parallel suprathermal electron fluxes are not a necessary condition for identification of closed field lines in the solar wind. In the present case the origin of the imbalance simply is the mixing of strahls of substantially different strengths from a different solar source each side of the HCS. The inferred exhaust orientations and distances of each spacecraft relative to the X-line show that the exhaust was likely non-planar, following the Parker spiral orientation. Finally, the separatrix layers and exhausts properties at each spacecraft suggest that the magnetic reconnection X-line location and/or reconnection rate were variable in both space and time at such large scales.
The Ion And Neutral Camera (INCA) sensor of the Cassini Magnetospheric Imaging Instrument (MIMI) ... more The Ion And Neutral Camera (INCA) sensor of the Cassini Magnetospheric Imaging Instrument (MIMI) may be configured either as an energetic neutral atom (ENA) camera, or as a sensitive energetic ion sensor. During the distant approach of Cassini to Saturn, the ENA emission from Saturn is too weak to take advantage of the ENA imaging capability of INCA, and so it was configured to measure 10-200 keV/nucleon energetic ions in the solar wind. INCA is easily the most sensitive instrument in this energy range to have measured heliospheric energetic ions in the region between Jupiter and Saturn. The measurements are dominated by ions accelerated at interplanetary shocks, as both coronal mass ejections and corotating interaction regions pass the Cassini spacecraft. The angular distributions of these ions have not been fully charaterized over most of this region, as Cassini remained typically 3-axis oriented and INCA can measure only over a 90o x 120o field of view. From the beginning of 2004...
1] Cluster CIS ion spectrograms measured during the period of the recent solar minimum between . ... more 1] Cluster CIS ion spectrograms measured during the period of the recent solar minimum between . We demonstrate how the background counts produced by energetic particles of the radiation belts in Cluster CIS and Double Star HIA instruments can be interpreted to obtain the locations of the boundaries of the outer and inner belts. The obtained L-MLT distribution of boundaries reflects the general structure of the radiation belts. Closer examination of the time-dependent L locations of the boundaries reveals several dips to lower L-shells (from L = 6 to L = 4) in the outer boundary location. The importance of the solar wind pressure increases for the Earthward shift of the outer boundary of the outer belt is discussed. The location and thickness of the slot region are studied using the determined inner boundaries of the outer belt and the outer boundaries of the inner belt. It was found that during intervals of low activity in the solar wind parameters, the slot region widens, which is consistent with weaker inward radial diffusion, and also with weaker local acceleration that can occur only at higher L-shells outside the plasmasphere. We conclude that boundaries of radiation belts determined from background measurements on the instruments with energy ranges that do not cover the radiation belts' energies provide valuable additional information that is useful for radiation belts' model development and validation. Citation: Ganushkina, N. Y., I. Dandouras, Y. Y. Shprits, and J. Cao (2011), Locations of boundaries of outer and inner radiation belts as observed by Cluster and Double Star,
1] How the solar wind affects the location of the magnetopause has been widely studied and excell... more 1] How the solar wind affects the location of the magnetopause has been widely studied and excellent models of the magnetopause based on in situ observations in the solar wind and at the magnetopause have been established, while the careful insight into the responses of the magnetopause to the variations in the solar wind can still provide us some new information about the processes in space plasmas. The short distance from Cluster to TC-1 on 9 March 2004, between 06:10 and 08:10 UT, gives us a good opportunity to precisely monitor the responses of the magnetopause to the variations in the solar wind. On the basis of the combined observations between Cluster, TC-1, and SuperDARN we analyze the magnetopause crossings associated with magnetopause motion or magnetic reconnection when the solar wind conditions have a series of variations. New results about the time delays for the propagation from the solar wind monitor to the magnetopause of the interplanetary magnetic fields (IMF) and of the solar wind dynamic pressure, respectively, and the intrinsic time for reconnection onset at the magnetopause are obtained. The most important feature of the event is that the dynamic pressure and the IMF in the solar wind do not arrive at the magnetopause at the same time, which will direct us to find out how the variation in the solar wind dynamic pressure is transported from the bow shock to the magnetopause. Another significant feature is that this event presents a shorter intrinsic time, ∼2 min, for reconnection onset at the dayside magnetopause than that given by the previous work of Le et al. (2011), Magnetopause response to variations in the solar wind: Conjunction observations between Cluster, TC-1, and SuperDARN,
1] We present a small statistical data set, where we investigate energy conversion at the magneto... more 1] We present a small statistical data set, where we investigate energy conversion at the magnetopause using Cluster measurements of magnetopause crossings. The Cluster observations of magnetic field, plasma velocity, current density and magnetopause orientation are needed to infer the energy conversion at the magnetopause. These parameters can be inferred either from accurate multispacecraft methods, or by using single-spacecraft methods. Our final aim is a large statistical study, for which only single-spacecraft methods can be applied. The Cluster mission provides an opportunity to examine and validate single-spacecraft methods against the multispacecraft methods. For single-spacecraft methods, we use the Generic Residue Analysis (GRA) and a standard one-dimensional current density method using magnetic field measurements. For multispacecraft methods, we use triangulation (Constant Velocity Approach -CVA) and the curlometer technique. We find that in some cases the single-spacecraft methods yield a different sign for the energy conversion than compared to the multispacecraft methods. These sign ambiguities arise from the orientation of the magnetopause, choosing the interval to be analyzed, large normal current and time offset of the current density inferred from the two methods. By using the Finnish Meteorological Institute global MHD simulation GUMICS-4, we are able to determine which sign is likely to be correct, introducing an opportunity to correct the ambiguous energy conversion values. After correcting the few ambiguous cases, we find that the energy conversion estimated from single-spacecraft methods is generally lower by 70% compared to the multispacecraft methods.
Several hot flow anomaly (HFA) like events were observed by STEREO magnetometer (MAG) and solar w... more Several hot flow anomaly (HFA) like events were observed by STEREO magnetometer (MAG) and solar wind thermal proton (PLASTIC) and electron (SWEA) instruments during the Earth orbit phase of STEREO B in February-March, 2007. The magnetic signature of the tangential discontinuities (TDs) was observed but the resolution of PLASTIC is not sufficient to identify the events without any doubt. The events are identified using the simultaneous measurements of the Cluster fluxgate magnetometer (FGM), ion (CIS/HIA) and resonance sounder (WHISPER) instruments. No HFA events were observed so far from the Earth before and these events are in the very late phase of HFA development. The comparison of these events using data acquired by Cluster and STEREO is a unique opportunity for studying the HFA characteristics far from its generation region, its turbulent features and its spatial-temporal development.
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Papers by I. Dandouras