Alfven waves in magnetospheric plasma: Micropulsations and particle acceleration

The non-uniformity of plasma density and magnetic fields is an important feature of the magnetospheric plasma. An Alfven wave acquires very unique features while propagating in such a plasma and exhibits interesting new phenomena Like resonant mode coupling, resonant absorption and resonant mode conversion. The theoretical analysis of the Alfven wave equation governing the dynamics of a linear inhomogeneous plasma system at low frequencies is discussed to understand these phenomena associated with the Alfven wave. The resonant mode coupling of shear Alfven waves both to steady and time-dependent sources is then related to understand the origin and characteristics features of micropulsations. The resonant mode conversion of an Alfven wave to a kinetic Alfven wave (KAW) having a wavelength comparable to the ion gyroradius in a direction perpendicular to the magnetic field is discussed. As a KAW has a component of its electric field in the direction of the ambient magnetic field it can accelerate plasma particles along the field. The basic theory of the mechanism of particle acceleration by KAW and a possible application of this type of acceleration mechanism to the formation of the aurora arcs is discussed.