A New Mechanism for Magnetic Hole Structures

Abstract:

Finite moments of decreased magnetic field strength, dubbed magnetic holes, are observed in-situ in the Earth’s magnetosphere, particularly in the bursty bulk flow braking region. The generation mechanism of magnetic holes has been investigated and multiple theories have been proposed. There are two popular theories: magnetic holes are the product of the mirror instability (Southwood and Kivelson 1993) or the product of the shear instability in the tail of the magnetosphere (Balikhin et al 2012). These theories are contingent on instabilities on the MHD scale. This study investigates THEMIS electric field and electron temperature observations of small magnetic holes in the bursty bulk flow region. An analysis of these observations indicate that smaller magnetic holes ( < ion Larmor radius) require a physical mechanism on the kinetic scale. We propose that these particular holes are maintained by a current carried by electrons, which are in turn generated by a self –consistent potential drop within the magnetic hole.