The nonlinear acceleration of a magnetic disturbance in the solar corona

Abstract

The simple form of Ohm's law (SI units)J = σ(E+ v × B)is valid for high density magnetofluids (where the mean free path for collisions is less than the Larmor radius) but is not strictly valid for the tenuous solar corona. We examine the nonlinear evolution of a magnetic disturbance using a more general form of Ohm's law which includes the Hall term. The Hall term dominates MHD development in the corona when the product of the magnetic scale length and the square root of the density is small enough; in particular when (1) the electron density is less than about 10¹³ m^-3 and (2) the scale length is less than a few hundred meters. For these parameters, a magnetic disturbance may carry electrons at a drift speed in excess of the Alfvén speed. We believe this nonlinear phenomenon may be important for the impulsive acceleration of charged particles in the solar corona.