Alfvénic plasma velocity variations observed at the inner edge of the low-latitude boundary layer induced by the magnetosheath mirror mode waves: A THEMIS observation

Abstract

With unique simultaneous observations both in the magnetosheath and magnetosphere by the THEMIS probes, Alfvénic variations in the plasma velocity are observed at the inner edge of low-latitude boundary layer (LLBL) and are induced by the mirror mode waves in the magnetosheath near the subsolar magnetopause on 31 July 2007. These Alfvénic variations appeared as the wavy perturbations in the Vx and Vy components observed by THEMIS C, D, and E, which had the same periodicity as associated magnetic field variations. Simultaneously, THEMIS B observed the mirror mode waves in the magnetosheath. The periodicities of the magnetic and plasma pressure variations of mirror modes in the magnetosheath were consistent with those of the Alfvénic wavy variations in the LLBL. Therefore, the mirror mode waves can induce the magnetopause undulations, launching Alfvén waves, and resultant Alfvénic variations are observed in the LLBL. Also, in the succeeding magnetosheath interval by THEMIS B, we examined whether the mirror mode waves occurred and associated Alfvénic variations were observed in the LLBL. However, no clear evidence for an existence of the mirror mode waves was obtained, and THEMIS C, D, and E do not also observe associated magnetic field and plasma Alfvénic responses in the LLBL. These results suggest that the Alfvénic variations in the LLBL are strongly related to the mirror mode waves in the magnetosheath. On the basis of these results, we emphasize that the magnetosheath energy is transmitted and transported into the magnetosphere via magnetopause surface waves. Copyright 2009 by the American Geophysical Union.