Multipoint study of magnetosheath magnetic field fluctuations and their relation to the foreshock

摘要

The magnetosheath is occupied with a variety of low-frequency fluctuations from different sources. Among them, the bow shock and dominantly foreshock processes are often considered as their major contributors. We use distant (Wind) and close (Geotail) interplanetary magnetic field monitors and compare their measurements with simultaneous magnetic field observations within the dawn (Time History of Events and Macroscale Interactions During Substorms (THEMIS)) and dusk (Cluster) magnetosheath. We have found that coherent low-frequency (10-4-10-3 Hz) variations can be registered in all locations; thus, their source is in the solar wind. On the other hand, no correlation was found for fluctuations of higher frequencies (up to 10~(-1) Hz); therefore, these fluctuations should be generated by local sources. We suggest that one of these sources is connected with magnetopause processes because the fluctuation amplitude grows toward the magnetopause.