Whistler wave generation by electron temperature anisotropy during magnetic reconnection at the magnetopause

Abstract. A new mechanism to generate whistler waves in the course of collisionless magnetic reconnection is proposed. It is found that intense whistler emissions occur in association with plasmoid collisions. The key processes are strong perpendicular heating of the electrons through a secondary magnetic reconnection during plasmoid collision and the subsequent compression of the ambient magnetic field, leading to whistler instability due to the electron temperature anisotropy. The emissions have a bursty nature, completing in a short time within the ion timescales, as has often been observed in the Earth's magnetosphere. The whistler waves can accelerate the electrons in the parallel direction, contributing to the generation of high-energy electrons. The present study suggests that the bursty emission of whistler waves could be an indicator of plasmoid collisions and the associated particle energization during collisionless magnetic reconnection.

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Role of electron temperature anisotropy in the onset of magnetic reconnection

Geophysical Research Letters ◽

10.1029/2004gl020791 ◽

2004 ◽

Vol 31 (18) ◽

Cited By ~ 38

Author(s):

H. Karimabadi

Keyword(s):

Electron Temperature ◽

Magnetic Reconnection ◽

Temperature Anisotropy

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A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet

Annales Geophysicae ◽

10.5194/angeo-27-395-2009 ◽

2009 ◽

Vol 27 (1) ◽

pp. 395-405 ◽

Cited By ~ 2

Author(s):

K. G. Tanaka ◽

K. Haijima ◽

M. Fujimoto ◽

I. Shinohara

Keyword(s):

Electron Temperature ◽

Magnetic Reconnection ◽

Current Sheet ◽

Time Scale ◽

Large Scale ◽

Saturation Level ◽

Small Island ◽

Ion Temperature ◽

Temperature Anisotropy ◽

A Current

Abstract. How to trigger magnetic reconnection is one of the most interesting and important problems in space plasma physics. Recently, electron temperature anisotropy (αeo=Te⊥/Te||) at the center of a current sheet and non-local effect of the lower-hybrid drift instability (LHDI) that develops at the current sheet edges have attracted attention in this context. In addition to these effects, here we also study the effects of ion temperature anisotropy (αio=Ti⊥/Ti||). Electron anisotropy effects are known to be helpless in a current sheet whose thickness is of ion-scale. In this range of current sheet thickness, the LHDI effects are shown to weaken substantially with a small increase in thickness and the obtained saturation level is too low for a large-scale reconnection to be achieved. Then we investigate whether introduction of electron and ion temperature anisotropies in the initial stage would couple with the LHDI effects to revive quick triggering of large-scale reconnection in a super-ion-scale current sheet. The results are as follows. (1) The initial electron temperature anisotropy is consumed very quickly when a number of minuscule magnetic islands (each lateral length is 1.5~3 times the ion inertial length) form. These minuscule islands do not coalesce into a large-scale island to enable large-scale reconnection. (2) The subsequent LHDI effects disturb the current sheet filled with the small islands. This makes the triggering time scale to be accelerated substantially but does not enhance the saturation level of reconnected flux. (3) When the ion temperature anisotropy is added, it survives through the small island formation stage and makes even quicker triggering to happen when the LHDI effects set-in. Furthermore the saturation level is seen to be elevated by a factor of ~2 and large-scale reconnection is achieved only in this case. Comparison with two-dimensional simulations that exclude the LHDI effects confirms that the saturation level enhancement is due to the ion anisotropy effects, while the LHDI effects shorten the overall time scale significantly. The results imply that the ion temperature anisotropy is one of the key properties that enable large-scale magnetic reconnection to develop in a super-ion-scale current sheet.

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MMS observations of electron firehose fluctuations in the magnetic reconnection outflow

10.5194/egusphere-egu21-14401 ◽

2021 ◽

Author(s):

Giulia Cozzani ◽

Yuri Khotyaintsev ◽

Daniel Graham ◽

Mats André

Keyword(s):

Energy Conversion ◽

Electron Temperature ◽

Magnetic Reconnection ◽

Diffusion Region ◽

Temperature Anisotropy ◽

Plasma Dynamics ◽

Background Magnetic Field ◽

Outflow Region ◽

Reconnection Site

Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy Te,&#160;> Te,perp&#160;(with respect to the background magnetic field) and produce nonpropagating oblique modes.&#160;Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements.&#160;We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 di distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.

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