Marginal stability of thin current sheets in the Earth's magnetotail

Experimental findings of the last decade shed new light on the physics of the magnetotail plasma system, e.g. investigation of very thin current sheets, and motivated a number of theoretical studies. An example of such theoretical investigations is the analytical 1D collisionless self-consistent model of thin current sheet [Zelenyi L.M., Malova, H.V., Popov, V.Yu., Delcourt, D., Sharma, A.S. 2004. Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy. Nonlinear Processes in Geophysics 11, 1–9]. The principal characteristic of this model is its anisotropy (typical features of thin current sheet). Because anisotropic current sheets have larger free energy than Harris’ ones, we decided to revisit the classical problem of their stability. The linear tearing instability, as the most natural mechanism for the spontaneous reconnection of magnetic field lines, is investigated in the frame of our anisotropic model. We search for regions in the parameter space of the current sheet where the system could become unstable. The main region of instability is concentrated near Bn∼0.1B0 and its width depends on the parameters of the system. This result conforms with an earlier work by Galeev and Zeleny [1976. Tearing instability in plasma configurations. Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 70(6), 2133–2151(in Russian)], which suggested that tearing mode could develop in a limited region of Bn values (however, these gaps were erroneously ascribed to Harris equilibrium). Therefore, the current investigation of the stability of anisotropic current sheets in the magnetotail could help to extend the previous results about the stability of Harris-like current sheets with magnetized electrons, and have implications for the physics of substorm initiation.