Abstract

Plasma jets are important carriers of mass and magnetic flux and are favorable regions for development of various waves and instabilities in Earth’s magnetotail. Here we conduct a comprehensive investigation of electron temperature anisotropy constraints from electron microinstabilities inside magnetotail jets. We find that data distributions (temperature anisotropy vs. electron parallel beta) are well constrained by electron microinstability thresholds, with stronger magnetic fluctuations near the instability thresholds, providing direct evidence for the operation of microinstability instabilities. We reveal that the jets’ leading and inner regions typically host stronger magnetic fluctuations than their trailing regions, indicating that the microinstabilities are typically developed in association with jets’ interaction with ambient plasma. We find that instability-related magnetic fluctuations generally become weaker during the jets’ Earthward propagation, indicating gradual relaxation of the jets’ free energy. These results suggest that electron microinstabilities play an important role in controlling electron thermodynamics in plasma jets.

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