Solar wind-magnetosphere-ionosphere coupling: Signal arrival time and perturbation relations

Abstract

On the basis of a simple one-dimensional model, we describe the sequence of the perturbations of different quantities from the magnetopause to the ionosphere after reconnection at the magnetopause has been switched on. Reconnection produces perturbations in the electric field, current, magnetic field, and plasma velocity. These perturbations extend over a broad frequency range, and each frequency band propagates at its group velocity to the ionosphere. The first perturbations to arrive at the ionosphere are mainly electromagnetic oscillations carried by the highest frequencies, whose front can propagate as fast as the speed of light if reconnection has switched on sufficiently suddenly, although it may propagate at the whistler-mode speed if reconnection switches on only on the whistler-mode timescale. The front of oscillations predominantly in the current arrives next, at the whistler-mode speed. Perturbations predominantly in the magnetic field and the velocity as well as nonoscillatory (step-function) changes of all the quantities arrive last, at the Alfvén speed. The ionosphere starts responding after the arrival of the electromagnetic front, although the dominant changes occur after the arrival of the Alfvén front. Copyright 2002 by the American Geophysical Union.