Spatial distributions of the ion to electron temperature ratio in the magnetosheath and plasma sheet

Abstract

[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,

Jets Downstream of Collisionless Shocks

“…The plasma sheet contains closed magnetic field lines and has an approximately isotropic plasma pressure (Wang et al 2012), which is nearly constant along the plasma tube. For a plasma nearly frozen into the magnetic flux tube the plasma tube entropy parameter (S = P V 5/3 , where V is the volume of unit magnetic flux tube) is approximately conserved during the earthward contraction of a finite-volume tube.…”

Profiles of electron temperature and <I>B</I><sub>z</sub> along Earth's magnetotail

“…So far, estimates of the gradient ∂/∂X in the magnetotail have been obtained by using three independent approaches: (1) small-scale gradients of the near-Earth dipolarized CS can be estimated using direct measurements of Cluster mission in 2007(Nakamura et al, 2009 or THEMIS mission in the case of specific spacecraft configuration (Saito et al, 2010;Panov et al, 2012); (2) statistical investigation can give average profiles of the main CS parameters (B z component, plasma pressure and plasma density) along the tail (see statistics collected by AMPTE/IRM, Geotail and THEMIS spacecraft in Kan and Baumjohann, 1990;Wang et al, 2012); and (3) thermal electrons could be used as Published by Copernicus Publications on behalf of the European Geosciences Union. tracers of the magnetotail structure (Artemyev et al, 2011c).…”

“…tracers of the magnetotail structure (Artemyev et al, 2011c). The distribution of electron temperature along the magnetotail was studied only using statistical investigation (e.g., Wang et al, 2012). Each of these methods has principal disadvantages for the determination of the gradient ∂/∂X in the magnetotail: (1) direct calculation of ∂/∂X is possible only for relatively strong gradients in the dipolarized CS; (2) average profiles cannot give snapshot-like information about the magnetotail structure (the latter is important because major tail parameters vary in a wide range on timescales from minutes to hours); and (3) to use electrons as tracers, one needs realistic models of the electron heating and detailed information about the transverse structure of CS.…”

Contribution of patchy reconnection to the ion to electron temperature ratio in the Earth's magnetotail

“…Using THEMIS data, Wang et al (2012) analyzed the dependence of the ion to electron temperature ratio on the local time and radial distance from the Earth, and found that the ratio e i T T decreases from~4 to~2 as AE increases from 10 to 1000. In addition, when plasma sheet plasma is warm during southward IMF period, a comparison of the specific entropies between the distant-and near-Earth tail suggested that non-adiabatic processes energize the electrons more than the ions, which leads to a lower e i T T ratio at smaller radial distances.…”