Compressional ULF waves in the outer magnetosphere: 2. A case study of Pc 5 type wave activity

摘要: In previously published work (Zhu and Kivelson, 1991) the spatial distribution of compressional magnetic pulsations period 2 - 20 min in outer magnetosphere was described. this companion paper, we study some specific events within our data set, seeking to determine structure waves identifying wave generation mechanism. We use both field three-dimensional plasma observed by ISEE 1 and/or spacecraft characterize eight ULF with frequencies below 8 mHz magnetosphere. High time resolution for event July 24, 1978, made possible a detailed analysis waves. Wave properties can be summarized as follows: (1) Partial pressures different energy ranges responded pressure differently. low-energy range they oscillated phase pressure, while oscillations higher-energy were out-of-phase; (2) Perpendicular wavelengths determined 60,000 30,000 km radial azimuthal directions, respectively. common all Compressional Pc 5 activity is correlated β, ratio pressure; absolute magnitude plays aminor role activity; The equator node perturbation field; (3) criterion mirror mode instability often satisfied near when are present. believe these generated internal MHD instabilities.