Abstract
Abstract. We study the electron temperature distribution and the structure of the current sheet along the magnetotail using simultaneous observations from THEMIS spacecraft. We perform a statistical study of 40 crossings of the current sheet when the three spacecraft THB, THC, and THD were distributed along the tail in the vicinity of midnight with coordinates XB ∈ [−30 RE, −20 RE], XC ∈ [−20 RE, −15 RE], and XD ~ −10 RE. We obtain profiles of the average electron temperature ⟨Te⟩ and the average magnetic field ⟨Bz⟩ along the tail. Electron temperature and ⟨Bz⟩ increase towards the Earth with almost the same rates (i.e., ratio ⟨Te⟩/⟨Bz⟩ ≈ 2 keV/7 nT is approximately constant along the tail). We also use statistics of 102 crossings of the current sheet from THB and THC to estimate dependence of Te and Bz distributions on geomagnetic activity. The ratio ⟨Te ⟩/⟨Bz⟩ depends on geomagnetic activity only slightly. Additionally we demonstrate that anisotropy of the electron temperature ⟨T∥/T⊥⟩ ≈ 1.1 is almost constant along the tail for X ∈ [−30 RE, −10 RE].
Highlights
Data Systems So far, estimates of the gradient ∂D/∂aXtainSthyesmteamgnestotail have been obtained by using three independent approaches:(1) small-scale gradients of the near-Earth Ddiispcoulsasriioznesd CSThe current sheet (CS) of the near-Earth magnetotail (−10 RE < X < −30 RE, where RE is the EGarteh orasdicusie) cnatnific bmeaianpgprraodxiiemnat taelloyngcotnhseidneorremdaal sdMiareoc2t-diDoensl(tarDulocnetugvreZe)wloaintphdmtthheeent can be estimated using direct measuGreemoenstscoifeCnlutisftiecr mission sion in in2t0h0e7c–a2s0e09of(NspaekcaMimficuorsadpeaetcalelc.Dr,a2fe0t 0vc9oe)nlofiorgTpuHrmaEtiMeonnIS(tSmaiitsoet al., 2010; Panov et al, 2012); (2) statisticDalisicnuvsessiotingsation weak gradient along x-direction (GSM coordinate system is used)
For each CS crossing from THEMIS dataset, we use the average values of Te, T /T⊥, and Bz component of the magnetic field computed in the central region of CS (|Bx| < 10 nT), where Te = (T + 2T⊥)/3, and T and T⊥ represent diagonal components of the electron temperature tensor
We have shown the following: (1) electron temperature in the vicinity of the neutral plane increases with Bz almost linearly, and (2) anisotropy of the electron temperature is almost constant along the tail for X ∈ [−25 RE, −10 RE]
Summary
Data Systems So far, estimates of the gradient ∂D/∂aXtainSthyesmteamgnestotail have been obtained by using three independent approaches:. 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. In this paper we use the statistics of simultaneous observations of thin CSs from several THEMIS spacecraft to study the relation between Te(X) and Bz(X) distributions
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