Tearing instabilities driven by nonideal effects in the tail plasma sheet

摘要

Using an extended magnetohydrodynamic description, the excitation of tearing modes is analytically investigated in the tail plasma sheet region that includes the magnetic field components B_(0x)(x,z) and B_(0z)(x,z). Taking electron inertia and the Hall effect into account, a generalized technique is displayed for obtaining the tearing solutions near the singular layer, where the B_(0x)(x,z) field reverses sign at z=0. In two-dimensional tail geometry for scale lengths of order c/ω_(pe), it is shown that a localized tearing mode as well as a mode with broad spatial extent (△'-driven mode) is excited near the field reversal region and these modes are mainly driven by electron inertia. For appropriate current sheet parameters, it is found that the localized mode becomes unstable in a couple of minutes while the mode with broad spatial width grows faster in 10 s. For three-dimensional perturbations wherein k_x,k_y≠0, the combined effects of the Hall term and the electron inertia are shown to excite new localized tearing modes with considerably enhanced growth rates (γ>ω_(ci)).