Abstract
Recently, it was argued that Hall conductivity and peak intensity of equivalent ionospheric currents are sensitive to the amount of field-aligned acceleration of plasma sheet (PS) electrons, which in turn depends on the plasma sheet parameters T e and N e (electron temperature and density) proportionally to the quantity eTN = (T e)1/2/N e. Here we extend these studies using data from six tail seasons of THEMIS observations to show statistically that the behavior of these PS electron parameters, measured in the middle of the nightside plasma sheet at ~10 RE distance, depends in a very different way on two basic processes: the solar wind state and substorms. We confirm previous work that slow/dense (fast/tenuous) solar wind provides cold/dense (hot/tenuous) plasma sheet conditions. However, we find that electron temperature and pressure parameters (T e and P e) behave differently from the proton ones (T p and P p), indicating a strong decoupling between temperature variations of auroral protons and electrons in the central plasma sheet (CPS): electrons are more sensitive to the substorm-related acceleration in the magnetotail than protons. Our superposed epoch study of plasma sheet parameter variations during substorms as well as our analysis of plasma acceleration at dipolarization fronts shows that during the substorm expansion phase a new (accelerated and plasma-depleted) population comes into the inner CPS with the flow bursts, showing an average increase of electron temperature and eTN parameter roughly by a factor of 2 above its background values for both cold/dense and hot/tenuous plasma sheet states. Preferential electron heating in the flow bursts is also statistically confirmed.
Highlights
It was argued that Hall conductivity and peak intensity of equivalent ionospheric currents are sensitive to the amount of field-aligned acceleration of plasma sheet (PS) electrons, which in turn depends on the plasma sheet parameters Te and Ne proportionally to the quantity eTN = (Te)1/2/Ne
Our study provides the quantitative estimates of the electron central plasma sheet (CPS) parameter variations in the region between 9 and 12 RE on the nightside, which are caused by two different factors: the solar wind state and substorms
We analyzed the multi-year dataset of THEMIS at 9–12 RE in the nightside plasma sheet combined with the OMNI data
Summary
We confirm previous work that slow/dense (fast/tenuous) solar wind provides cold/dense (hot/tenuous) plasma sheet conditions. We find that electron temperature and pressure parameters (Te and Pe) behave differently from the proton ones (Tp and Pp), indicating a strong decoupling between temperature variations of auroral protons and electrons in the central plasma sheet (CPS): electrons are more sensitive to the substorm-related acceleration in the magnetotail than protons. Our superposed epoch study of plasma sheet parameter variations during substorms as well as our analysis of plasma acceleration at dipolarization fronts shows that during the substorm expansion phase a new (accelerated and plasma-depleted) population comes into the inner CPS with the flow bursts, showing an average increase of electron temperature and eTN parameter roughly by a factor of 2 above its background values for both cold/dense and hot/tenuous plasma sheet states. Preferential electron heating in the flow bursts is statistically confirmed
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