A theoretical study of type Pi 2 geomagnetic micropulsations

Abstract

Pi 2 pulsations are long period magnetic oscillations superimposed onto the geomagnetic field. They are usually associated with the onset of auroral substorms. To gain an understanding of the generation of Pi 2 pulsations, an instability mechanism and a transient response mechanism are studied. The instability mechanism results from a deceleration of magnetospheric convection in the plasma sheet while the transient response mechanism arises from an enhancement of magnetospheric convection in the plasma sheet. Both mechanisms are reviewed and a one-dimensional wave equation is solved numerically to model the transient response mechanism. The numerical computations indicate that a rapid enhancement of the magnetospheric convection will launch Alfven waves which will produce an oscillating current in the ionosphere. Model results for the transient response mechanism indicate that the oscillating current can produce Pi 2 pulsations with periods that compare favorably with ground based measurements.