[1] The global distribution and spectral properties of electromagnetic ion cyclotron (EMIC) waves in the He + band are simulated for the 21 April 2001 storm using a combination of three different codes: the Rice Convection Model, the Ring current-Atmospheric interactions Model, and the HOTRAY ray tracing code (incorporated with growth rate solver). During the storm main phase, injected ions exhibit a non-Maxwellian distribution with pronounced phase space density minima at energies around a few keV. Ring current H + injected from the plasma sheet provides the source of free energy for EMIC excitation during the storm. Significant wave gain is confined to a limited spatial region inside the storm time plume and maximizes at the eastward edge of the plume in the dusk and premidnight sector. The excited waves are also able to resonate and scatter relativistic electrons, but the minimum electron resonant energy is generally above 3 MeV.

[1] We have used THEMIS measurements to determine how the ion and electron temperatures and their ratio (T i /T e ) change spatially in the magnetosheath and plasma sheet and to identify the processes responsible for the variations. Magnetosheath T i /T e varies from $4-12 with higher ratios observed during larger solar wind speed and at locations closer to the magnetopause. T i /T e remains almost unchanged as particles flow downstream and cool adiabatically. Across the flank magnetopause from the magnetosheath to a plasma sheet that is cool with abundant cold plasma, temperature and specific entropy for ions and electrons increase significantly while T i /T e remains similar, indicating that the magnetosheath ions and electrons are non-adiabatically energized with similar proportion while entering the magnetosphere. Within the tail plasma sheet, T i /T e varies from $6 to 10 when plasma is relatively cool to $2 to 5 when relatively warm. With this correlation, T i /T e is higher closer to the flanks and during northward interplanetary magnetic field (IMF), while lower T i /T e is more often seen during higher AE around midnight. The distinguishably lower T i /T e for warmer plasma in the near-Earth plasma sheet is likely due to additional non-adiabatic heating of electrons more than ions as particles move earthward and are adiabatically energized. As particles move into the near-Earth magnetosphere, strengthening magnetic drift brings more hotter ions toward dusk and more hotter electrons toward dawn, resulting in a strong T i /T e dawn-dusk asymmetry with very high T i /T e ($15 to 100) near dusk and very low T i /T e ($1) near dawn.Citation: Wang, C.-P., M. Gkioulidou, L. R. Lyons, and V. Angelopoulos (2012), Spatial distributions of the ion to electron temperature ratio in the magnetosheath and plasma sheet,

[1] To understand the nightside plasma sheet structure under different interplanetary magnetic field (IMF) B z conditions, we have investigated statistically the equatorial distributions of ions and magnetic fields from Geotail when the IMF has been continuously northward or southward for shorter or longer than 1 hour. A dawn-dusk density (temperature) asymmetry with higher density (temperature) on the dawn (dusk) side is seen in the near-Earth plasma sheet during northward IMF, resulting in roughly dawn-dusk symmetric pressure. As southward IMF proceeds, the density asymmetry weakens while the temperature asymmetry maintains, resulting in higher pressure on the dusk side. The plasma sheet is relatively colder and denser near the flanks than around midnight. The flux distributions show that the density asymmetry is due to ions <$3 keV, and the temperature asymmetry is due to ions above thermal energy. The perpendicular flow shows that ions divert around the Earth mainly through the dusk side in the inner plasma sheet because of westward diamagnetic drift. The magnetic fields indicate that field lines are more stretched during southward IMF. Ions' electric and magnetic drift paths evaluated from the observations show that for thermal energy ions, magnetic drift is as important as electric drift. Comparison of the distributions of the observed phase space density with the evaluated drift paths at different energies indicates that the electric and magnetic drift transport is responsible for the observed dawn-dusk asymmetries in the plasma sheet structure.

Substorms release a large amount of energy, some of which is used to energize the precipitating particles in the polar region. Superposed epoch analysis was performed with 11 years of DMSP SSJ/4/5 data to characterize the substorm cycle of the diffuse, monoenergetic, and broadband/wave precipitating electrons and precipitating ions. Although substorms only increase the ion pressure by 30%, they increase the power of the diffuse, monoenergetic, and wave electron aurora by 310%, 71%, and 170%, respectively. Substorms energize the ion aurora mainly in the 21:00–05:00 magnetic local time (MLT) sector. The dynamics of the diffuse electron aurora are different from those of the other two electron aurorae. The expansion phase duration is approximately 15 min for the monoenergetic and wave electron aurorae, whereas it is 1 h for the diffuse electron aurora. The monoenergetic and wave electron aurorae appear to complete the substorm cycle within a 5 h interval, whereas the diffuse electron aurora takes more than 5 h. The diffuse electron aurora power and energy flux start increasing at 15 min before the substorm onset, whereas those for the monoenergetic and wave electron aurorae start increasing at 1 h and 15 min before the onset. The increase in the monoenergetic electron aurora power and energy flux may result from the increase in the magnetotail stretching and region‐1 field‐aligned current during the growth phase. The monoenergetic electrons may also be associated with fast flows, which have been previously observed more frequently in the dusk‐midnight sector.

[1] To understand the large-scale plasma sheet thermodynamics, we have used Geotail data and a formula for estimating flux tube volume V to investigate statistically the equatorial distributions of PV 5/3 and nV for slow flowing plasma in the nightside plasma sheet and compare them with the physical bases of ideal MHD and the Rice Convection Model (RCM). We have examined the distributions under three conditions: (1) weak convection and low AE, (2) enhanced convection and low AE, and (3) enhanced convection and high AE. The overall nV decreases significantly with increasing convection or AE, while the overall PV 5/3 remains similar. We found that PV 5/3 drops significantly earthward along the estimated electric drift paths near midnight, inconsistent with ideal MHD. Examination of P k V 5/3 and the electric and magnetic drift paths of different energy invariants, where P k is the partial pressure of a specific energy invariant, shows that the strong duskward drift of the above thermal-energy particles due to magnetic drift, together with there being significantly fewer higher-energy particles from the dawn flank than from the tail, results in the strong earthward decrease of PV 5/3 . We also found that d(P k V

The composition of the inner magnetosphere is of great importance for determining the plasma pressure and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two auroral electrojet levels based on over 60 months of observations from the Helium, Oxygen, Proton, and Electron and Radiation Belt Storm Probes Ion Composition Experiment mass spectrometers onboard Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high auroral electrojet levels with hydrogen pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn‐dusk asymmetry with ion pressures peaking at dusk and electron pressure peaking at dawn. In addition, ring current hydrogen with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet (>90%) and active times (>60%), while oxygen with 10 < E < 50 keV and electrons with 0.1 < E < 40 keV become important during active times contributing more than 25% and 20% on the nightside, respectively, while the helium contribution is generally small. The results presented in this study provide a global picture of the equatorial plasma pressure distributions and the associated contributions from different species with different energy ranges, which advance our knowledge of wave generation and provide models with a systematic baseline of plasma composition.

[1] The goal of this paper is to understand the formation of the Harang reversal and its association with the region 2 field-aligned current (FAC) system, which couples the plasma sheet transport to the ionosphere. We have run simulations with the Rice convection model (RCM) using the Tsyganenko 96 magnetic field model and realistic plasma sheet particle boundary conditions on the basis of Geotail observations. Our results show that the existence of an overlap in magnetic local time (MLT) of the region 2 upward and downward FAC is necessary for the formation of the Harang reversal. In the overlap region the downward FAC, which is located at lower latitudes, is associated with low-energy ions that penetrate closer to Earth toward the dawn side, while the upward FAC, which is located at higher latitudes, is associated with high-energy ions. Under the same enhanced convection we compare the Harang reversal resulting from a hotter and more tenuous plasma sheet with the one resulting from a colder and denser plasma sheet. For the former case the shielding of the convection electric field is less efficient than for the latter case, allowing low-energy protons to penetrate further earthward, resulting in a Harang reversal that extends to lower latitudes, expands wider in MLT, and is located further equatorward than the upward FAC peak and the conductivity peak. The return flows of the Harang reversal in the hot and tenuous case are located in a low conductivity region. This leads to an enhancement of these westward flows, resulting in subauroral polarization streams (SAPS).

[1] We have investigated the Geotail data statistically to understand the particle sources, transport, and spatial distributions of the plasma sheet ions and electrons of different energies during northward interplanetary magnetic field (IMF), and their dependences on the solar wind density (N sw ), the solar wind speed (V sw ), and the magnitude of the northward IMF B z (jB z,IMF j). We find that the plasma sheet becomes colder and denser, indicating a larger increase in the cold than in the hot population, with increasing N sw or jB z,IMF j or with decreasing V sw . The cold population dominates the region near the flanks while the hot population dominates the near-midnight region, which is consistent with the plasma sheet plasma being a mixture of cold particles coming from the flanks and hot particles from the distant-tail. The phase space densities show that the flank source strongly depends on jB z,IMF j, while the tail source strongly depends on V sw . Cold particles from the dawn flank to midnight increase significantly with decreasing V sw , but no significant changes are seen near the dusk flank, suggesting a dependence of the solar wind entry through the dawn flank on V sw . The comparisons between the distributions of the phase space density and the electric and magnetic drift paths estimated from the observations indicate that the thermal and high-energy particles are mainly transported by electric and magnetic drift, while other transport mechanisms, such as diffusion, may play a role in transporting the low energy particles from the flank sources to midnight.