Search

Spacecraft formation flying in co-planar identical orbits with oppositely directed apse lines (eccentricity vectors) allows simultaneous in-situ measurements in different altitudes and time-sequential measurements in a limited altitude range (rapid revisit); a key enabling factor in understanding many poorly understood phenomena in our atmosphere and its interaction with the magnetosphere. The dynamics and control problem for flying formations in mirrored orbits are investigated using the Mechanisms of Energetic Mass Ejection - Explorer (MEME-X) mission concept as a case study. It is determined that the proposed two-craft and four-craft configurations require routine maintenance to correct their relative motion. The formation maintenance costs are quantified for both configurations and determined to be within the capabilities of small satellites. A high-fidelity end-to-end simulation is developed to model the entire two-craft mission concept, from orbit insertion to decommissioning, providing an approximate baseline for the flight dynamics costs of similar missions using multiple spacecraft flying in mirrored orbits.

STR acknowledges support from the ISSI international team Cold plasma of ionospheric origin in the Earth's magnetosphere and of the Ministry of Economy and Competitiveness (MINECO) of Spain (grant FIS2017-90102-R). Research at IRAP was supported by CNRS, CNES and the University of Toulouse. JHL and DLT acknowledge support from NASA Grant 80NSSC18K1378. RED was supported by NASA grants 80NSSC19K070 and 80NSSC19K0254. MA was supported by SNSA Grant 56/18. SKV and RCA acknowledge support from NASA Grant 80NSSC19K0270. Work performed by MMS team members is supported by NASA contract NNG04EB99C., We report observations of the ion dynamics inside an Alfvén branch wave that propagates near the reconnecting dayside magnetopause. The measured frequency, wave normal angle and polarization are consistent with the predictions of a dispersion solver. The magnetospheric plasma contains hot protons (keV), cold protons (eV), plus some heavy ions. While the cold protons follow the magnetic field fluctuations and remain frozen-in, the hot protons are at the limit of magnetization. The cold protons exchange energy back and forth, adiabatically, with the wave fields. The cold proton velocity fluctuations contribute to balance the Hall term fluctuations in Ohm's law, and the wave E field has small ellipticity and right-handed polarization. The dispersion solver indicates that increasing the cold proton density facilitates propagation and amplification of these waves at oblique angles, as for the observed wave., ISSI international team Cold plasma of ionospheric origin in the Earth's magnetosphere, Ministry of Economy and Competitiveness (MINECO) of Spain FIS2017-90102-R, Centre National de la Recherche Scientifique (CNRS), European Commission, Centre National D'etudes Spatiales, University of Toulouse, National Aeronautics & Space Administration (NASA) 80NSSC18K1378 80NSSC19K070 80NSSC19K0254 80NSSC19K0270 NNG04EB99C, SNSA 56/18

We investigate the energy conversion and partition in the asymmetric reconnection diffusion region using two-dimensional particle-in-cell simulations and Magnetosphere Multiscale (MMS) mission observations. Under an upstream condition with equal temperatures in the two inflow regions, the simulation analysis indicates that the energy partition between ions and electrons depends on the distance from the X-line. Within the central electron diffusion region (EDR), nearly all dissipated electromagnetic field energies are converted to electrons. From the EDR to the ion diffusion region (IDR) scales, the rate of the electron energy gain decreases to be lower than that of ions. A magnetopause reconnection event inside the IDR observed by MMS shows comparable ion and electron energy gains, consistent with the simulation result in the transition region from EDR to IDR. At the EDR scale, the electron energization is mainly by the reconnection electric field (E(sub r)); in-plane electric fields (E(sub xz)) provide additional positive contributions near the X-line and do negative work on electrons beyond the EDR. The guide field reduces the electron energization by both E(sub r) and E(sub xz) in the EDR. For ion energization, E(sub r) and E(sub xz) have comparable contributions near the time of the peak reconnection rate, while E(sub xz) dominants at later time. At the IDR scale, the guide field causes asymmetry in the amount of the energy gain and energization mechanisms between two exhausts but does not have significant effects on energy partition. Our study advances understanding of ion and electron energization in asymmetric reconnect IDRs.

International audience; The Electron Diffusion Region (EDR) is the region where magnetic reconnection is initiated and electrons are energized. Because of experimental difficulties, the structure of the EDR is still poorly understood. A key question is whether the EDR has a homogeneous or patchy structure. Here we report Magnetospheric MultiScale (MMS) novel spacecraft observations providing evidence of inhomogeneous current densities and energy conversion over a few electron inertial lengths within an EDR at the terrestrial magnetopause, suggesting that the EDR can be rather structured. These inhomogenenities are revealed through multi-point measurements because the spacecraft separation is comparable to a few electron inertial lengths, allowing the entire MMS tetrahedron to be within the EDR most of the time. These observations are consistent with recent high-resolution and low-noise kinetic simulations.

The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm‐3 and the H+ density is 20% due to mass‐loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions. publishedVersion

The structure of asymmetric magnetopause reconnection is explored with multiple point and high-time-resolution ion velocity distribution observations from the Magnetospheric Multiscale mission. On 9 September 2015, reconnection took place at the magnetopause, which separated the magnetosheath and the magnetosphere with a density ratio of 25:2. The magnetic field intensity was rather constant, even higher in the asymptotic magnetosheath. The reconnected field line region had a width of approximately 540 km. In this region, streaming and gyrating ions are discriminated. The large extension of the reconnected field line region toward the magnetosheath can be identified where a thick layer of escaping magnetospheric ions was formed. The scale of the magnetosheath side of the reconnected field line region relative to the scale of its magnetospheric side was 4.5:1.

Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an “ambipolar” electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an “electric wind” must be considered when studying the evolution and potential habitability of any planet in any star system.

Magnetic holes are ubiquitous in space plasmas, occurring in the solar wind, downstream of planetary bow shocks, and inside the magnetosphere. Recently, kinetic-scale magnetic holes have been observed near Earth's central plasma sheet. The Fast Plasma Investigation on NASA's Magnetospheric Multiscale (MMS) mission enables measurement of both ions and electrons with 2 orders of magnitude increased temporal resolution over previous magnetospheric instruments. Here we present data from MMS taken in Earth's nightside plasma sheet and use high-resolution particle and magnetometer data to characterize the structure of a subproton-scale magnetic hole. Electrons with gyroradii above the thermal gyroradius but below the current layer thickness carry a current sufficient to account for a 10-20 depression in magnetic field magnitude. These observations suggest that the size and magnetic depth of kinetic-scale magnetic holes is strongly dependent on the background plasma conditions.

Lion roars are narrowband whistler wave emissions that have been observed in several environments, such as planetary magnetosheaths, the Earth's magnetosphere, the solar wind, downstream of interplanetary shocks, and the cusp region. We present measurements of more than 30,000 such emissions observed by the Magnetospheric Multiscale spacecraft with high‐cadence (8,192 samples/s) search coil magnetometer data. A semiautomatic algorithm was used to identify the emissions, and an adaptive interval algorithm in conjunction with minimum variance analysis was used to determine their wave vector. The properties of the waves are determined in both the spacecraft and plasma rest frame. The mean wave normal angle, with respect to the background magnetic field (B(sub 0)), plasma bulk flow velocity (V(sub b)), and the coplanarity plane (V(sub b) × B(sub 0)) are 23°, 56°, and 0°, respectively. The average peak frequencies were ∼31% of the electron gyrofrequency (ω(sub ce)) observed in the spacecraft frame and ∼18% of ω(sub ce) in the plasma rest frame. In the spacecraft frame, ∼99% of the emissions had a frequency

著者人数: 49名(所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 齋藤, 義文), Accepted: 2018-11-06, 資料番号: SA1180352000

Using a global multifluid MHD model, we demonstrate the effects of magnetospheric O+ on bursty magnetotail flows. We carry out two simulations without ionospheric outflow to use as baseline, one driven by real solar wind data and one driven by idealized solar wind. Solar wind data from 1 October 2001 are used as a storm time solar wind driver. During this event, the plasma sheet was observed to be rich in O+, making the event of interest for a model analysis of the effects of ionospheric origin O+ on magnetospheric dynamics. We carry out outflow comparison simulations for both the realistic and idealized solar wind drivers using a simple empirical model that places auroral outflow in regions where downward propagating Poynting flux and electron precipitation are present, combined with a low-flux thermal energy O+ outflow over the entire polar region. We demonstrate the effects of O+ on magnetotail structure and the occurrence rate and strength of bursty, fast earthward flows. The addition of O+ to the magnetotail stretches the tail and increases the velocity of bursty earthward flows. This increase is shown to be produced by reconnection events in an extended current sheet created by tail stretching.

International audience; We analyzed 20 reconnection events observed by the Magnetosphere MultiScale mission, finding that in a subregion of the magnetospheric inflow, the electron temperature parallel to the magnetic field (Te||) decreases toward the separatrix with increasing densities. Such Te|| variation is not consistent with the heating through the parallel potential mechanism for magnetospheric electrons. Associated with the change in Te||, low-energy gyrotropic magnetosheath-like electrons are observed. These electrons may come from the magnetosheath, penetrate to the magnetospheric side possibly due to waves in the lower hybrid frequency range, and do not experience as much energization as those from deeper in the magnetosphere. In addition, as Te|| decreases, the high-energy field-aligned phase-space densities decrease or fluctuate significantly over time. Wave-particle interaction might produce energy conversion and cause the high-energy phase-space density variations.

Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth׳s magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O + , load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.

A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth's magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space - magnetosheath, shock, foreshock and pristine solar wind - featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the 'Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)'. THOR has been selected by European Space Agency (ESA) for the study phase. Funding: The THOR science team thanks the Swedish National Space Board for support to carry out a technical assessment phase study before the proposal submission. We acknowledge the useful discussion and comments from the THOR team (http://thor.irfu.se/team) and particularly D. Delcourt, D. Fontaine, A. Kis, G. Lapenta, M. Maksimovic, M. Opher, G. Paschmann, A. Petrukovic, S. Schwartz. We acknowledge: the support of the UK Space Agency through grant ST/N003322/1 to ICL; the support of Agenzia Spaziale Italiana through contract ASI-INAF 2015-039-R.O to University of Calabria, Italy and at IAPS/INAF, Rome; the support of the Belgian Science Policy Office through PRODEX PEA 4000116805 to BIRA-IASB; the support of the Czech Science Foundation through project 16-04956S to Charles University, Prague; the support of ESA PRODEX to IAP Prague; the support of CNRS and CNES to IRAP, LPP, LP2CE and LESIA; the support of the German Space Agency through grant 50 00 1603 to CAU; the support of Swedish National Space Board through grants 232/15 and 257/15 to IRF, Uppsala; the support of Academy of Finland through grant 267144 and European Research Council Consolidator through grant 682068-PRESTISSIMO to FMI; the support of ISSI team 'Kinetic Turbulence and Heating in the Solar wind'; the support of FP7 projects STORM and SHOCK. Vlasiator (http://vlasiator.fmi.fi) has been developed with the support of Academy of Finland and European Research Council Starting grant 200141-QuESpace.

Because of the small planetary magnetic field as well as proximity to the Sun that leads to enhanced solar wind pressure as compared to Earth, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. We investigate the dynamics of magnetospheric ions during such compression events. Using three-dimensional single-particle simulations, we show that the electric field induced by the time varying magnetic field can lead to significant ion energization, up to several hundreds of eVs or a few keVs. This energization occurs in a nonadiabatic manner, being characterized by large enhancements of the ion magnetic moment and bunching in gyration phase. It is obtained when the ion cyclotron period is comparable to the field variation time scale. This condition for nonadiabatic heating is realized in distinct regions of space for ions with different mass-to-charge ratios. During compression of Mercury's magnetosphere, heavy ions originating from the planetary exosphere may be subjected to such an abrupt energization, leading to loading of the magnetospheric lobes with energetic material.

The plasma sheet, inner magnetosphere, and high-latitude magnetosphere all contain significant amounts of O + ions during active times. Singly charged oxygen ions unambiguously come from the ionosphere, making them an excellent tracer species. We test the cleft ion fountain theory, which asserts that O + ions escape from the cleft, cross the polar cap, and then enter the plasma sheet. Statistical studies of O + density in the cleft, high-altitude polar cap, and plasma sheet all indicate that the O + density increases with increasing solar wind dynamic pressure. In order to examine O + transport more directly, we use polar cap ion outflow measurements and the 2001 Tsyganenko magnetic field model driven with advanced composition explorer (ACE) solar wind parameters. We calculate the distance between the cleft and the ionospheric footpoints of magnetic field lines mapped from the polar spacecraft along the noon–midnight meridian. Using the observed outflow speed and the magnetic field line length we calculate the travel time for the ions. When we examine the distance from the cleft versus the O + travel time for individual passes, the slope of the line is consistent with the measured ionospheric convection speed across the polar cap. We conclude that O + ions emanating principally from the cleft are transported across the polar cap, and these O + ions have access to the ring current and plasma sheet.

We investigate the dynamics of charged particles in the dayside magnetosphere in response to abrupt variations of the solar wind dynamical pressure. Using test particle simulations, we show that the electric field induced by the compression of the frontside magnetosphere may be responsible for prominent energization of plasma sheet ions as well as trapping at high latitudes. We demonstrate that, due to the short-lived character of the magnetic field line reconfiguration (on the time scale of a few minutes), the particle magnetic moment (first adiabatic invariant) may not be conserved during such events. Ions that are initially bouncing from one hemisphere to the other are found to experience nonadiabatic energization up to the hundred of keV range while being injected into the outer cusp. Such injections involve particles from limited portions of the dayside flux tubes. The energetic particles that are produced in the outer cusp during such events subsequently circulate about the field minimum at high latitudes without intercepting the equatorial plane, thus contributing to the high-energy populations that are observed in this region of space.

We report results of a statistical study correlating ionized solar wind (ISW) fluxes observed by ACE during late 2000 and throughout 2001 with neutral solar wind (NSW) fluxes observed by IMAGE/LENA over the same period. The average correlation coefficient between the neutral and ionized solar wind is 0.66 with correlations greater than 0.80 occurring about 29% of the time. Correlations appear to be driven by high solar wind flux variability, similar to results obtained by in situ multi-spacecraft correlation studies. In this study, however, IMAGE remains inside the magnetosphere on over 95% of its orbits. As a function of day of year, or equivalently ecliptic longitude, the slope of the relationship between the neutral solar wind flux and the ionized solar wind flux shows an enhancement near the upstream direction, but the symmetry point appears shifted toward higher ecliptic longitudes than the interstellar neutral (ISN) flow direction by about 20°. The estimated peak interstellar neutral upstream density inside of 1 AU is about 7 × 10−3 cm−3.

We examine the circulation of heavy ions of planetary origin within Mercury’s magnetosphere. Using single particle trajectory calculations, we focus on the dynamics of sodium ions, one of the main species that are ejected from the planet’s surface. The numerical simulations reveal a significant population in the near-Mercury environment in the nightside sector, with energetic (several keV) Na + densities that reach several tenths cm-3 at planetary perihelion. At aphelion, a lesser (by about one order of magnitude) density contribution is obtained, due to weaker photon flux and solar wind flux. The numerical simulations also display several features of interest that follow from the small spatial scales of Mercury’s magnetosphere. First, in contrast to the situation prevailing at Earth, ions in the magnetospheric lobes are found to be relatively energetic (a few hundreds of eV), despite the low-energy character of the exospheric source. This results from enhanced centrifugal acceleration during E × B transport over the polar cap. Second, the large Larmor radii in the mid-tail result in the loss of most Na + into the dusk flank at radial distances greater than a few planetary radii. Because gyroradii are comparable to, or larger than, the magnetic field variation length scale, the Na + motion is also found to be non-adiabatic throughout most of Mercury’s equatorial magnetosphere, leading to chaotic scattering into the loss cone or meandering (Speiser-type) motion in the near-tail. As a direct consequence, a localized region of energetic Na + precipitation develops at the planet’s surface. In this region which extends over a wide range of longitudes at mid-latitudes ( ~ 30°–40°), one may expect additional sputtering of planetary material.Key words. Magnetospheric physics (planetary magnetospheres) – Space plasma physics (charged particle motion and acceleration; numerical simulation studies)

During periods of increased geomagnetic activity, cold and dense plasmaspheric material is observed to drain from the inner magnetosphere toward the dayside magnetopause. Geosynchronous observations have shown that plasmaspheric material may participate in the dayside reconnection. However, predictions of plasmaspheric material passing through the polar region on recently opened field lines have not yet been confirmed by observations. We present evidence for the existence of such plasmaspheric material on high-latitude open magnetic field lines based on our investigations of 20 months of Interball/Hyperboloid observations and 11 months of Polar/ Thermal Ion Dynamics Experiment (TIDE) observations. In order to distinguish plasmaspheric material from the low-energy portion of entering magnetosheath plasma from the solar wind, observed phase-space densities are compared to modeled magnetosheath and plasmaspheric phase-space densities. The phase-space density distribution function of magnetosheath ions is estimated from upstream solar wind parameters using the gasdynamic theory. Twenty-one events were found in which Interball passed through open field lines on the dayside during periods of increased geomagnetic activity, two of which show evidence for the presence of plasmaspheric material. Additionally, six such events were identified from the Polar/TIDE database. Although the occurrence frequency is low, evidence of cold plasmaspheric material being transported on high-latitude open field lines does exist.

We correlate solar wind and IMF properties with the properties of O(+) and H(+) in the polar cap in early 1996 during solar minimum conditions at altitudes between 5.5 and 8.9 Re geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the POLAR satellite. Throughout the high altitude polar cap, we observe H(+) to be more abundant than O(+). H(+) is a significant fraction of both the ionosphere and the solar wind, and O(+) is not a significant species in the solar wind. O(+) is the major species in the ionosphere so the faction of O(+) present in the magnetosphere is commonly used as a measure of the ionospheric contribution to the magnetosphere. For these reasons, 0+ is of primary interest in this study. We observe O(+) to be most abundant at lower latitudes when the solar wind speed is low (and low Kp), and at higher solar wind speeds (and high Kp) O(+) is observed across most of the polar cap. We also find that O(+) density and parallel flux are well organized by solar wind dynamic pressure; they both increase with solar wind dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, but H(+) density and parallel flux have some negative correlation with IMF By, and some positive correlation with VswBIMF. In this solar minimum data set, H(+) is dominant so that contributions of this plasma to the plasma sheet would have a very low O(+) to H(+) ratio.

We report observations of low energy neutral atoms (LENA) from the solar wind and the ionosphere, obtained by the LENA Imager on the IMAGE spacecraft. The LENA Imager detects and images LENAs arriving at the spacecraft from within a 90° field of view (8° × 8° pixels), swept through 360° every two minutes by spacecraft spin. Neutral atoms arriving at the sensor are converted to negative ions by a conversion surface. The resulting negative ions are separated in energy (3 bins, 10–250 eV) and arrival direction (±45°). They are then accelerated, detected, and time-of-flight mass analyzed. The solar wind and the ionosphere both emit measurable neutral atom fluxes, the latter responding rapidly to to variations of the former.

The classical pure radial diffusion mechanism appears not to fully explain the frequently observed rapid enhancement in the timescales of minutes to hours in the radiation belt electron fluxes in the Earth's magnetosphere. We here consider other physical mechanisms, such as energization mechanisms associated with substorm processes, to account for these sudden increases. A three-dimensional electron kinetic model is used to simulate the dynamics of the geomagnetically trapped population of radiation belt electrons during a substorm injection event. In the past this model has been extensively used to study dynamics of energetic ions in the ring current. This work, for the first time, constitutes the development of a combined convection and diffusion model to radiation belt electrons in the 0.04–4 MeV kinetic energy range. The Tsyganenko 89 geomagnetic field model is used to simulate the time-varying terrestrial magnetosphere during the growth phase elongation and the expansion phase contraction. We find that inductive electric field associated with the magnetic reconfiguration process is needed in order to transport substorm electrons into the trapped particle region of the magnetosphere. The maximum enhancement in energetic electron fluxes is found to be located around the geosynchronous orbit location (L = 6.6), with up to 2 orders of magnitude enhancement in the total fluxes (0.04–4 MeV). Although this enhancement in the inner magnetosphere is very sensitive to the temperature and, to a less extent, density of the source population in the plasma sheet, we suggest that the substorm-associated energization in the magnetotail and the subsequent adiabatic acceleration in the earthward region account for the enhanced MeV electrons (killer electrons) seen at the geosynchronous orbit during storms and substorms.

The IMAGE spacecraft uses photon and neutral atom imaging and radio sounding techniques to provide global images of Earth's inner magnetosphere and upper atmosphere. Auroral imaging at ultraviolet wavelengths shows that the proton aurora is displaced equatorward with respect to the electron aurora and that discrete auroral forms at higher latitudes are caused almost completely by electrons. Energetic neutral atom imaging of ions injected into the inner magnetosphere during magnetospheric disturbances shows a strong energy-dependent drift that leads to the formation of the ring current by ions in the several tens of kiloelectron volts energy range. Ultraviolet imaging of the plasmasphere has revealed two unexpected features—a premidnight trough region and a dayside shoulder region—and has confirmed the 30-year-old theory of the formation of a plasma tail extending from the duskside plasmasphere toward the magnetopause.

The discovery of terrestrial O+ and other heavy ions in magnetospheric hot plasmas, combined with the association of energetic ionospheric outflows with geomagnetic activity, led to the conclusion that increasing geomagnetic activity is responsible for filling the magnetosphere with ionospheric plasma. Recently it has been discovered that a major source of ionospheric heavy ion plasma outflow is responsive to the earliest impact of coronal mass ejecta upon the dayside ionosphere. Thus a large increase in ionospheric outflows begins promptly during the initial phase of geomagnetic storms, and is already present during the main phase development of such storms. We hypothesize that enhancement of the internal source of plasma actually supports the transition from substorm enhancements of aurora to storm-time ring current development in the inner magnetosphere. Other planets known to have ring current-like plasmas also have substantial internal sources of plasma, notably Jupiter and Saturn. One planet having a small magnetosphere, but very little internal source of plasma, is Mercury. Observations suggest that Mercury has substorms, but are ambiguous with regard to the possibility of magnetic storms of the planet. The Messenger mission to Mercury should provide an interesting test of our hypothesis. Mercury should support at most a modest ring current if its internal plasma source is as small as is currently believed. If substantiated, this hypothesis would support a general conclusion that the magnetospheric inflationary response is a characteristic of magnetospheres with substantial internal plasma sources. We quantitatively define this hypothesis and pose it as a problem in comparative magnetospheres.

More than 30 years after the prediction of the polar wind outflow from the high latitude ionosphere, the exact magnitude and ultimate fate of the ionospheric plasma supply remains unknown. Estimates made more than a decade ago suggested that the polar ion outflow might well be of sufficient strength to populate the different regions of the Earth’s magnetosphere. Direct measurements in the high altitude magnetosphere became possible only with the launch of the Polar spacecraft. The combination of the Thermal Ion Dynamics Experiment and the Plasma Source Instrument has revealed the presence of low energy (

Centrifugal acceleration of escaping ionospheric plasma is one of the important and fundamental processes responsible for energizing and transporting ionospheric plasma to all regions of the magnetosphere. Normally this mechanism operates over extremely large distances. Because of this feature and limitations in particle instrumentation, it has not been possible to directly confirm from in-situ plasma measurements the very specific predictions made by basic plasma theory about centrifugal acceleration. We report here data obtained near Polar satellite apogee over the northern polar cap during a magnetospheric compression event that occurred on September 24, 1998. Between 2345:18 and 2347:18 UT the magnetic field rotated by about 20° and increased in intensity. The Toroidal Imaging Mass-Angle Spectrograph (TIMAS) instrument on Polar obtained bulk velocity moments of preexisting upflowing H+, O+, He+, and He++ ions with enough precision and resolution to directly demonstrate, together with computer simulation, that the magnitude and direction of changes in plasma motion during this event follow directly from the changes in the magnetic field configuration as predicted by the equations describing centrifugal acceleration.

On September 24, 1998 at 2345 UT the magnetosphere was suddenly compressed as the dynamic pressure of the solar wind rapidly rose from 2 to 15 nPa. At the Polar spacecraft, at high altitudes above the center of the northern polar cap, a remarkably smooth increase in the field strength occurred while the plasma properties changed abruptly, as described in an accompanying paper. Comparisons with models and an examination of the wave amplitudes during the compression indicate that the initial change in plasma properties was most probably due to convection of pre-existing boundary layer plasma to the location of Polar rather than due to local heating by betatron acceleration and ion cyclotron waves. The smoothness of the increase in field strength is attributed to the very high velocity of compressional waves in the tail that outrun the advancing solar wind disturbance. The signatures as measured by GOES 10 at 1444 LT and at GOES 8 at 1846 LT in low latitude geosynchronous orbit are the more familiar sudden jump on the dayside, where the density is high and the compressional wave velocity low, and a weak change on the nightside, where tail current changes oppose the effects of the dayside magnetopause currents. This event is an ideal candidate for collaborative investigation of the effects of a classical sudden storm commencement on the magnetosphere.

We report observations of a direct ionospheric plasma outflow response to the incidence of an interplanetary shock and associated coronal mass ejection (CME) upon the earth's magnetosphere. Data from the WIND spacecraft, 185 RE upstream, document the passage of an interplanetary shock at 23:20 UT on 24 Sept. 1998. The polar cap plasma environment sampled by the POLAR spacecraft changed abruptly at 23:45 UT, reflecting the compressional displacement of the geopause relative to the spacecraft. POLAR left the polar wind outflow region and entered the mantle flows. Descending toward the dayside cusp region, POLAR later returned from the mantle to an enhanced polar wind flux dominated by O+ plasma and eventually containing molecular ions. The enhanced and O+− dominated outflow continued as the spacecraft passed through the high altitude cleft and then the southern cleft at lower altitude. Such a direct response of the ionosphere to solar wind dynamic pressure disturbances may have important impacts on magnetospheric dynamics.

The evolution of the inner plasma sheet and the ring current during substorm dipolarizations is simulated. A substorm cycle is treated by stretching and dipolarizing the magnetosphere according to the Tsyganenko 89 model. In order to clarify the relative influences of steady convection and induction electric field on ring current development, the inductive electric field is superposed on two baseline convective states: a nonstorm state using a weak electric field, and a storm-time state using a stronger electric field. Ion distributions on the nightside at 12 Earth radii (RE) during these two substorms are obtained using our single-particle code to trace particle trajectories backward in time to source regions assumed to have steady characteristics. The subsequent acceleration and transport of these boundary ions into the inner magnetosphere is modeled by our kinetic model of the ring current. The simulation generates many frequently observed features of substorm injections, including the sudden appearance of hot plasma tailward of a sharply defined "injection boundary," the earthward motion of an "injection front," the azimuthal and tailward expansion of this enhanced region, and the creation of characteristic ion dispersion patterns near geosynchronous orbit. Comparison of the nonstorm and storm cases suggests that substorms occurring without a convection enhancement produce mainly an enhancement of the cross-tail current but little change in the ring current. With strong convection, the role of substorms is to enable the convection enhancement to create robust ring current in the inner magnetosphere.

On May 29, 1996 from 0200 to 0800 UT the solar wind dynamic pressure was high ranging from 6 to 8 nPa and the interplanetary field was almost due northward, ranging from 10 to 15 nT in BZ GSM. Even at apogee the POLAR spacecraft should not have entered the magnetosheath according to recent scaling laws. However, the magnetic fieid was greatly depressed below the value expected indicating the presence of significant plasma energy density throughout the high latitude magnetosphere surrounding the cusp. The presence of this plasma is confirmed by the plasma instrumentation on board the spacecraft. While the entry into this nearly stagnant plasma was gradual, the exit on to polar cap field lines was abrupt. We interpret these observations in terms of the post-cusp reconnection of the strongly northward interplanetary magnetic field.

The development of the ring current ions in the inner magnetosphere during the main phase of a magnetic storm is studied. The temporal and spatial evolution of the ion phase space densities in a dipole field are calculated using a three dimensional ring current model, considering charge exchange and Coulomb losses along drift paths. The simulation starts with a quiet time distribution. The model is tested by comparing calculated ion fluxes with Active Magnetospheric Particle Tracer Explorers/CCE measurement during the storm main phase on May 2, 1986. Most of the calculated omnidirectional fluxes are in good agreement with the data except on the dayside inner edge (L < 2.5) of the ring current, where the ion fluxes are underestimated. The model also reproduces the measured pitch angle distributions of ions with energies below 10 keV. At higher energy, an additional diffusion in pitch angle is necessary in order to fit the data. The role of the induced electric field on the ring current dynamics is also examined by simulating a series of substorm activities represented by stretching and collapsing the magnetic field lines. In response to the impulsively changing fields, the calculated ion energy content fluctuates about a mean value that grows steadily with the enhanced quiescent field.

The Sounding of the Cleft Ion Fountain Energization Region (SCIFER) experiment was conducted to investigate the ionospheric origin of the Cleft Ion Fountain (CIF). In the previous decade several high altitude spacecraft studies concluded that the CIF is the principal source of mass for the magnetosphere, especially O+. Yet the ionospheric cleft in the altitude range between 1000 km and 2000 km had not been explored since the ISIS spacecraft experiments in the 1970s. SCIFER was designed to fill that gap with instrumentation that provided continuous spatial/temporal resolution two orders of magnitude better than that achieved by previous orbiting spacecraft.

We report direct observations of the three-dimensional velocity distribution of selected topside ionospheric ion species in an auroral context between 500 and 550 km altitude. We find heating transverse to the local magnetic field in the core plasma, with significant heating of 0(+), He(+), and H(+), as well as tail heating events that occur independently of the core heating. The 0(+) velocity distribution departs from bi-Maxwellian, at one point exhibiting an apparent ring-like shape. However, these observations are shown to be aliased within the auroral arc by temporal variations that arc not well-resolved by the core plasma instrument. The dc electric field measurements reveal superthermal plasma drifts that are consistent with passage of the payload through a series of vortex structures or a larger scale circularly polarized hydromagnetic wave structure within the auroral arc. The dc electric field also shows that impulsive solitary structures, with a frequency spectrum in the ion cyclotron frequency range, occur in close correlation with the tail heating events. The drift and core heating observations lend support to the idea that core ion heating is driven at low altitudes by rapid convective motions imposed by the magnetosphere. Plasma wave emissions at ion frequencies and parallel heating of the low-energy electron plasma are observed in conjunction with this auroral form; however, the conditions are much more complex than those typically invoked in previous theoretical treatments of superthermal frictional heating. The observed ion heating within the arc clearly exceeds that expected from frictional heating for the light ion species H(+) and He(+), and the core distributions also contain hot transverse tails, indicating an anomalous transverse heat source.

We investigate the transport of ions in the low-altitude magnetosphere magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury.

[1] To determine the characteristics and origin of observed storm-time electron density enhancements in the polar cap, and to investigate the spatial extent (noon-midnight direction) of associated O+ ion outflows, we analyzed nearly simultaneous observations of such electron density enhancements from the Akebono satellite and ion upflows from the Polar satellite during a geomagnetic storm occurring on 6 April 2000. The Akebono satellite observed substantial electron density enhancements by a factor of ∼10–90 with a long duration of ∼15 h at ∼2 RE in the southern polar region. The Polar satellite outflow measurements in the northern polar cap at ∼7–4 RE exhibited velocity filtering of the ∼100 eV to ∼0 eV (from the spacecraft potential) ion outflow from the cleft ion fountain, with resultant temperatures declining from ∼3 eV to 0.03 eV with increasing distance from the cusp. Similar velocity filtering was detected in the southern polar cap at ∼1.8–3.5 RE. The region of O+ ion outflows with fluxes exceeding 5×108 /cm2/s (mapped to 1000 km altitude) extended ∼10° MLAT (∼1000 km) at the ionosphere from the cusp/cleft into the dayside polar cap at ∼2.5 RE. These coordinated Akebono-Polar observations are consistent with the development of storm-time electron density enhancements in the polar cap as a result of the bulk outflow of low-energy plasma as part of the cleft ion fountain. The large spatial scale, large ion fluxes, and the long duration indicate significant supply of very-low-energy O+ ions to the magnetosphere through this region.

We investigate the effect of a rotation of the Interplanetary Magnetic Field (IMF) on the transport of magnetospheric ion populations at Mercury. We focus on ions of planetary origin and investigate their large-scale circulation using three-dimensional single-particle simulations. We show that a nonzero BX component of the IMF leads to a pronounced asymmetry in the overall circulation pattern. In particular, we demonstrate that the centrifugal acceleration due to curvature of the E × B drift paths is more pronounced in one hemisphere than the other, leading to filling of the magnetospheric lobes and plasma sheet with more or less energetic material depending upon the hemisphere of origin. Using a time-varying electric and magnetic field model, we investigate the response of ions to rapid (a few tens of seconds) re-orientation of the IMF. We show that, for ions with gyroperiods comparable to the field variation time scale, the inductive electric field should lead to significant nonadiabatic energization, up to several hundreds of eVs or a few keVs. It thus appears that IMF turning at Mercury should lead to localized loading of the magnetosphere with energetic material of planetary origin (e.g., Na+).

The superstorm on 20.21 November 2003 was the largest geomagnetic storm in solar cycle 23 as measured by Dst, which attained a minimum value of .422 nT. We have simulated this storm to understand how particles originating from the solar wind and ionosphere get access to the magnetosphere and how the subsequent transport and energization processes contribute to the buildup of the ring current. The global electromagnetic configuration and the solar wind H+ distribution are specified by the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics model. The outflow of H+ and O+ ions from the ionosphere are also considered. Their trajectories in the magnetosphere are followed by a test-particle code. The particle distributions at the inner plasma sheet established by the LFM model and test-particle calculations are then used as boundary conditions for a ring current model. Our simulations reproduce the rapid decrease of Dst during the storm main phase and the fast initial phase of recovery. Shielding in the inner magnetosphere is established at early main phase. This shielding field lasts several hours and then breaks down at late main phase. At the peak of the storm, strong penetration of ions earthward to L shell of 1.5 is revealed in the simulation. It is surprising that O+ is significant but not the dominant species in the ring current in our calculation for this major storm. It is very likely that substorm effects are not well represented in the models and O+ energization is underestimated. Ring current simulation with O+ energy density at the boundary set comparable to Geotail observations produces excellent agreement with the observed symH. As expected in superstorms, ring current O+ is the dominant species over H+ during the main to mid-recovery phase of the storm.

We revisit a reported "Ionospheric Mass Ejection" using prior event observations to guide a global simulation of local ionospheric outflows, global magnetospheric circulation, and plasma sheet pressurization, and comparing our results with the observed global response. Our simulation framework is based on test particle motions in the Lyon-Fedder-Mobarry (LFM) global circulation model electromagnetic fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere, and includes an embedded plasmaspheric simulation. Global circulation is stimulated using the observed solar wind conditions for the period 24-25 Sept 1998. This period begins with the arrival of a Coronal Mass Ejection, initially with northward, but later with southward interplanetary magnetic field. Test particles are launched from the ionosphere with fluxes specified by local empirical relationships of outflow to electrodynamic and particle precipitation imposed by the MIlD simulation. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the full equations of motion. Results are compared with the observed ring current and a simulation of polar and auroral wind outflows driven globally by solar wind dynamic pressure. We find good quantitative agreement with the observed ring current, and reasonable qualitative agreement with earlier simulation results, suggesting that the solar wind driven global simulation generates realistic energy dissipation in the ionosphere and that the Strangeway relations provide a realistic local outflow description.

We present simulation results from a one-way coupled global MHD model (Block-Adaptive-Tree Solar-Wind Roe-Type Upwind Scheme, BATS-R-US) and kinetic ring current models (Comprehensive Ring Current Model, CRCM, and Fok Ring Current, FokRC). The BATS-R-US provides the CRCM/FokRC with magnetic field information and plasma density/temperature at the polar CRCM/FokRC boundary. The CRCM uses an electric potential from the BATS-R-US ionospheric solver at the polar CRCM boundary in order to calculate the electric field pattern consistent with the CRCM pressure distribution. The FokRC electric field potential is taken from BATS-R-US ionospheric solver everywhere in the modeled region, and the effect of Region II currents is neglected. We show that for an idealized case with southward-northward-southward Bz IMF turning, CRCM-BATS-R-US reproduces well known features of inner magnetosphere electrodynamics: strong/weak convection under the southward/northward Bz; electric field shielding/overshielding/penetration effects; an injection during the substorm development; Subauroral Ion Drift or Polarization Jet (SAID/PJ) signature in the dusk sector. Furthermore, we find for the idealized case that SAID/PJ forms during the substorm growth phase, and that substorm injection has its own structure of field-aligned currents which resembles a substorm current wedge. For an actual event (12 August 2000 storm), we calculate ENA emissions and compare with Imager for Magnetopause-to-Aurora Global Exploration/High Energy Neutral Atom data. The CRCM-BATS-R-US reproduces both the global morphology of ring current and the fine structure of ring current injection. The FokRC-BATS-R-US shows the effect of a realistic description of Region II currents in ring current-MHD coupled models.

A review is given of recent (1987-1990) progress in understanding of the origins of plasmas in the earth's magnetosphere. In counterpoint to the early supposition that geomagnetic phenomena are produced by energetic plasmas of solar origin, 1987 saw the publication of a provocative argument that accelerated ionospheric plasma could supply all magnetospheric auroral and ring current particles. Significant new developments of existing data sets, as well as the establishment of entirely new data sets, have improved the ability to identify plasma source regions and to track plasma through the magnetospheric system of boundary layers and reservoirs. These developments suggest that the boundary between ionospheric and solar plasmas, once taken to lie at the plasmapause, actually lies much nearer to the magnetopause. Defining this boundary as the surface where solar wind and ionosphere contribute equally to the plasma, it is referred to herein as the 'geopause'. It is now well established that the infusion of ionospheric O(+) plays a major role in the storm-time distention of the magnetotail and inflation of the inner magnetosphere. After more than two decades of observation and debate, the question remains whether magnetosheric are protons of solar or terrestrial origin.

[1] Previous studies of the magnetospheric plasma populations have concentrated on the low-energy (1 eV) plasma of the plasmasphere, the more energetic (1-100 keV) plasma of the plasma sheet and ring current, and the high-energy (approximately MeV) plasma of the radiation belts. A compilation of satellite measurements over the past 30 years augmented by recent observations from the Polar-TIDE instrument has revealed a new perspective on a plasma population in the middle magnetosphere. This population consists of ions with energies of a few eV to greater than several hundred eV which display a characteristic bidirectional field-aligned pitch angle distribution. Measurements from the ATS, ISEE, SCATHA, DE, and POLAR satellites establish the characteristics of this “warm plasma cloak” of particles that is draped over the nightside region of the plasmasphere and is blown into the morning and early afternoon dayside sector by the sunward convective wind in the magnetosphere. The satellite observations combined with the predictions of an ion trajectory model are used to describe the formation and dynamics of the warm plasma cloak.

[1] Ions from the Earth's ionosphere are an important component of the coupled magnetosphere-ionosphere system. These ions are accelerated out of the ionosphere in the auroral zone. As they gain altitude, a fraction of them are charge exchanged, producing energetic neutrals. These neutrals (in the energy range from ∼10 to ∼300 eV) are imaged by the Low Energy Neutral Atom (LENA) imager on the Imager for Magnetopause to Aurora Global Exploration spacecraft. From these images, the instantaneous local time extent of the ion outflow is determined. These data show that, during times of substorm recovery, the local time extent of the outflow is large and variable, typically centered on the dayside, but often extending over nearly the entire auroral oval. The local time extent appears to encompass the ionospheric footprint of the cusp.

[1] We investigate the fate of a plasmaspheric plume generated by a discrete period of southward interplanetary magnetic field (IMF) to assess its contribution to plasma sheet and ring current pressure and compare with that for other sources. We use test particle motions in Lyon-Fedder-Mobarry (LFM) global circulation model fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) model of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere. A variant of the Ober plasmasphere model is embedded within the models and driven by them. Global circulation is stimulated by a period of southward IMF embedded within a long interval of northward IMF. This leads to the production of a well-defined plasmaspheric plume, enhancing the plasma density sunward of the plasmasphere. Test particles are launched with the properties of plasmaspheric ions on the L = 6.6 RE shell and weighted with densities as specified by the Ober model, as it responds to convection imposed by CRCM. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the Delcourt full equations of motion, implemented for finite element fields. Results are compared with earlier computations of polar and auroral wind outflows. The plume produces an enhanced flow of plasma ∼10 times the normal polar wind global fluence. However, we find that most of the “plasmaspheric wind” is lost from the magnetosphere such that its contribution to the ring current energy density is comparable to that of the normal polar wind for this type of event.

Observations from the Polar spacecraft, taken during a period of northward interplanetary magnetic field (IMF) show magnetosheath ions within the magnetosphere with velocity distributions resulting from multiple merging sites along the same field line. The observations from the TIDE instrument show two separate ion energy-time dispersions that are attributed to two widely separated (-20Re) merging sites. Estimates of the initial merging times show that they occurred nearly simultaneously (within 5 minutes.) Along with these populations, cold, ionospheric ions were observed counterstreaming along the field lines. The presence of such ions is evidence that these field lines are connected to the ionosphere on both ends. These results are consistent with the hypothesis that double merging can produce closed field lines populated by solar wind plasma. While the merging sites cannot be unambiguously located, the observations and analyses favor one site poleward of the northern cusp and a second site at low latitudes.

We review observations and theories of the solar ablation of planetary atmospheres, focusing on the terrestrial case where a large magnetosphere holds off the solar wind, so that there is little direct atmospheric impact, but also couples the solar wind electromagnetically to the auroral zones. We consider the photothermal escape flows known as the polar wind or refilling flows, the enhanced mass flux escape flows that result from localized solar wind energy dissipation in the auroral zones, and the resultant enhanced neutral atom escape flows. We term these latter two escape flows the "auroral wind." We review observations and theories of the heating and acceleration of auroral winds, including energy inputs from precipitating particles, electromagnetic energy flux at magnetohydrodynamic and plasma wave frequencies, and acceleration by parallel electric fields and by convection pickup processes also known as "centrifugal acceleration." We consider also the global circulation of ionospheric plasmas within the magnetosphere, their participation in magnetospheric disturbances as absorbers of momentum and energy, and their ultimate loss from the magnetosphere into the downstream solar wind, loading reconnection processes that occur at high altitudes near the magnetospheric boundaries. We consider the role of planetary magnetization and the accumulating evidence of stellar ablation of extrasolar planetary atmospheres. Finally, we suggest and discuss future needs for both the theory and observation of the planetary ionospheres and their role in solar wind interactions, to achieve the generality required for a predictive science of the coupling of stellar and planetary atmospheres over the full range of possible conditions.