Rapidly Moving Sources of Upper-Band ELF/VLF Chorus Near the Magnetic Equator

MANUEL PLATINO; UMRAN INAN; TIMOTHY BELL

Moscone Conference Center, San Francisco, California, Estados Unidos

Congreso; American Geophysical Union Fall Meeting; 2003

American Geophysical Union

The possibility to resolve the space - time fine structure of wave - particle interactions in the magnetosphere has been realized in the context of the CLUSTER mission. Multiple simultaneous measurements of upper band chorus emissions near the magnetic equator (at magnetic latitudes between -20$deg$ and 10$deg$ and L shells ranging between L = 4 and L = 5) have been carried out during 2001 - 2003. The first observations were reported by Gurnett et al. [2001], who showed that the same chorus elements on different spacecraft exhibited a distinctive difference in frequency. The unique characteristics of such measurements allow us to deduce key aspects of the mechanism of generation of ELF/VLF chorus emission. In the present paper we show that this frequency difference can be explained as a differential Doppler shift, using a simple model involving rapidly moving sources traveling at speeds comparable to the parallel resonant velocity of counter - streaming electrons moving along the Earth´s magnetic field lines. We report observations from the CLUSTER spacecraft of ELF/VLF upper - band chorus, and perform a study of the source characteristics of these waves based on frequency and time differences of the same elements recorded on different spacecraft, traveling with separations ranging from 600 km to 2000 km. These frequency and time differences are interpreted as a direct consequence of the rapid motion of highly localized source regions of chorus.