Propagation Characteristics of Lobe Trapped Continuum Radiation in the Distant Magnetotail

Lobe trapped continuum radiation (LTCR) has been observed by the plasma wave instrument onboard GEOTAIL spacecraft at frequencies as low as 1 kHz in the distant magnetotail. Detailed analysis of spectral structures of the LTCR has shown that it is most likely to be generated locally in the vicinity of the plasma sheet boundary layer (PSBL) and then trapped inside the tail lobe region. However, it has not been clear how the source locations of the LTCR distribute in the distant tail. A direction finding analysis has been used to estimate the source region of electromagnetic waves. From a direction finding analysis the arrival directions of the LTCR are almost parallel to the dawn-dusk direction. The propagation directions of the LTCR may not point out its source locations because of its ray path deformed by reflections at the high density regions such as the magnetopause and the plasma sheet. Therefore it is very important to know the propagation characteristics of the LTCR in the distant tail region. In this study, we perform a 3-D ray-tracing of the large scale LTCR propagation to understand the direction finding result. A 3-D ray tracing analysis shows that the initially radiated Sun-Earth ray directions of the LTCR are transformed into the dawn-dusk directions by the reflection at the cylindrical tail magnetopause. By comparing the results of the direction finding with the 3-D ray tracing analysis the possible source regions for the LTCR are the plasma sheet boundary layer away from the nominal tail axis and the low latitude boundary layer.