[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
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