MMS observations of electron firehose fluctuations in the magnetic reconnection outflow

Giulia Cozzani

The electron firehose (EF) instability is driven by electron temperature anisotropy $T_{e,||}>T_{e,\perp}$ (with respect to the background magnetic field) and produces nonpropagating oblique modes. Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities affecting the energy conversion of the process. Yet, the EF instability and its role in the reconnection process are still relatively unexplored in in situ data. We report MMS observations of EF fluctuations observed in the exhaust region of a reconnection site in the magnetotail, relatively close to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique EF fluctuations, the associated instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. We suggest that the EF fluctuations may be originated at the EDR and then advected in the outflow region