Dispersion analysis of low-frequency waves through the terrestrial bow shock

Abstract

We present dispersion relations of low-frequency waves observed upstream and downstream of the Earth's bow shock analyzing Cluster magnetometer measurements along an outbound orbit covering four regions: The foreshock, the outer, the middle, and the inner magnetosheath. The aim of our study is to better understand wave transmission, mode conversion, or wave excitation in the bow shock environment. The foreshock waves identified exhibit two wave modes propagating parallel to the magnetic field that are consistent with the right-hand ion beam instability, whereas the magnetosheath waves exhibit a transition from a mixture of ion cyclotron waves and mirror mode in the outer sheath into primarily mirror mode structures in the middle sheath. Properties of the mirror mode are distorted near the magnetopause probably due to effects of density gradients or plasma flow pattern imposed by the magnetopause. From the viewpoint of the dispersion relation, the propagation angle, and the polarization, the foreshock wave properties are not transmitted into the magnetosheath. Copyright 2005 by the American Geophysical Union.