Origin of low proton-to-electron temperature ratio in the Earth's plasma sheet

We study the proton-to-electron temperature ratio (Tp/Te) in the plasma sheet (PS) of the Earth's magnetotail using 5 years of Cluster observations (2001-2005). The PS intervals are searched within a region defined with -19 < X ≤ -7 RE and |Y| < 15 RE (GSM) under the condition |BX| ≤ 10 nT. One hundred sixty PS crossings are identified. We find an average value of <Tp/Te> 6.0. However, in many PS intervals Tp/Te varies over a wide range from a few units to several tens of units. In 86 PS intervals the Tp/Te decreases below 3.5. Generally, the decreases of Tp/Te are due to some increase of Te while Tp either decreases or remains unchanged. In the majority of these intervals the Tp/Te drops are observed during magnetotail dipolarizations. A superposed epoch analysis applied to these events shows that the minimum value of Tp/Te is observed after the dipolarization onset during the "turbulent phase" of dipolarization, when a number of transient BZ pulses are reduced, but the value of BZ is still large and an intensification of wave activity is observed. The Tp/Te drops, and associated increases of Te often coincide either with bursts of broadband electrostatic emissions, which may include electron cyclotron harmonics, or with broadband electromagnetic emission in a frequency range from proton plasma frequency (fpp) up to the electron gyrofrequency (fce). These findings show that the wave activity developing in the current sheet after dipolarization onset may play a role in the additional electron heating and the associated Tp/Te decrease.

@article{id2253,
  author = {Grigorenko, E. E. and Kronberg, E. A. and Daly, P. W. and Ganushkina, N. Yu. and Lavraud, B. and Sauvaud, J.-A. and Zelenyi, L.},
  doi = {10.1002/2016JA022874},
  journal = {JGR},
  language = {en},
  pages = {9985-10,004},
  title = {Origin of low proton-to-electron temperature ratio in the Earth's plasma sheet},
  volume = {121},
  year = {2016},
}

%O Journal Article
%A Grigorenko, E. E.
%A Kronberg, E. A.
%A Daly, P. W.
%A Ganushkina, N. Yu.
%A Lavraud, B.
%A Sauvaud, J.-A.
%A Zelenyi, L.
%R 10.1002/2016JA022874
%J JGR
%G en
%P 9985-10,004
%T Origin of low proton-to-electron temperature ratio in the Earth's plasma sheet
%V 121
%D 2016