Origin of low protonâ toâ electron temperature ratio in the Earth’s plasma sheet

We study the protonâ toâ electron temperature ratio (Tp/Te) in the plasma sheet (PS) of the Earth’s magnetotail using 5â years of Cluster observations (2001â 2005). The PS intervals are searched within a region defined with â 19â â ~â 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 â turbulent phaseâ 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.Key PointsDuring dipolarizations, drops of Tp/Teâ â ¤â 3.5 often coincide with wave bursts in the frequency range f~fceGenerally, the decreases of Tp/Te are due to some increase of Te while Tp either decreases or remains unchangedElectron heating by ECH and EME with fâ â ¤â fce can be an additional mechanism affecting the Tp/Te during dipolarizationsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135062/1/jgra53043_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135062/2/jgra53043.pd