Radial profile of pressure in a storm ring current as a function of D st

Abstract

Using satellite data obtained near the equatorial plane during 12 magnetic storms with amplitudes from −61 down to −422 nT, the dependences of maximum in L-profile of pressure (Lm) of the ring current (RC) on the current value of Dst are constructed, and their analytical approximations are derived. It is established that function Lm(Dst) is steeper on the phase of recovery than during the storm’s main phase. The form of the outer edge of experimental radial profiles of RC pressure is studied, and it is demonstrated to correspond to exponential growth of the total energy of RC particles on a given L shell with decreasing L. It is shown that during the storms’ main phase the ratio of plasma and magnetic field pressures at the RC maximum does not practically depend on the storm strength and Lm value. This fact reflects resistance of the Earth’s magnetic field to RC expansion, and testifies that during storms the possibilities of injection to small L are limited for RC particles. During the storms’ recovery phase this ratio quickly increases with increasing Lm, which reflects an increased fraction of plasma in the total pressure balance. It is demonstrated that function Lm(Dst) is derived for the main phase of storms from the equations of drift motion of RC ions in electrical and magnetic fields, reflecting the dipole character of magnetic field and scale invariance of the pattern of particle convection near the RC maximum. For the recovery phase it is obtained from the Dessler-Parker-Sckopke relationship. The obtained regularities allow one to judge about the radial profile of RC pressure from ground-based magnetic measurements (data on the Dst variation).