Sheared field tearing mode instability and creation of flux ropes in the Earth magnetotail

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Abstract
Spontaneous disruptions of magnetotail energy are supposed to be caused by a tearing mode instability. We show how the tail current sheet becomes unstable in the presence of a sufficiently large magnetic shear. The instability occurs because the magnetic shear removes the stabilizing influence of the gyroscopic electrons. Ion Landau damping determines the growth rate of the instability. A violation of the magnetic line conservation in a narrow region due to finite electron inertia would allow three—dimensional reconnection and flux rope formation. The resulting flux topes are smaller in size and cause, therefore, weaker and more localized perturbations of the magnetosphere.