Signatures of Mode Conversion and Kinetic Alfvén Waves at the Magnetopause
Authors: Jay R. Johnson and C.Z. Cheng
Date of PPPL Report: July 2000
Published in: Geophys. Res. Lett. 28 (January 2001) 227-230. (Author list changed to: Jay R. Johnson, C.Z. Cheng, and P. Song.)
It has been suggested that resonant mode conversion of compressional MHD waves into kinetic Alfvén waves at the magnetopause can explain the abrupt transition in wave polarization from compressional to transverse commonly observed during magnetopause crossings [Johnson and Cheng, 1997b]. We analyze magnetic field data for magnetopause crossings as a function of magnetic shear angle (defined as the angle between the magnetic fields in the magnetosheath and magnetosphere) and compare with the theory of resonant mode conversion. The data suggest that amplification in the transverse magnetic field component at the magnetopause is not significant up to a threshold magnetic shear angle. Above the threshold angle significant amplification results, but with weak dependence on magnetic shear angle. Waves with higher frequency are less amplified and have a higher threshold angle. These observations are qualitatively consistent with theoretical results obtained from the kinetic-fluid wave equations.