Cluster Observations Whistler-mode Propagation Inside and Outside the Plasmasphere

MANUEL PLATINO; UMRAN INAN; TIMOTHY BELL; DONALD GURNETT; JOLENE PICKETT

Moscone Conference Center, San Francisco, California, Estados Unidos

Congreso; American Geophysical Union Fall Meeting; 2004

American Geophysical Union

ELF/VLF Chorus emissions and lightning- generated whistlers are two types of whistler mode waves commonly detected in the inner regions of the Earth´s magnetosphere. Lightning-generated whistlers are generally observed in the region 2$<$L$<$6, while chorus is generally observed in the region 4$<$L$<$6. Studies of ELF/VLF chorus emissions observed near the magnetic equator have shown that their sources can be closely localized in space , while whistlers are known to be generated by lightning strikes on Earth, and can travel relatively longer distances into the magnetosphere with relatively broad wave fronts. Recently the Cluster spacecraft have provided a unique opportunity to obtain four simultaneous measurements of these ELF/VLF whistler mode waves at four separate points in space. In the present paper we use CLUSTER data to compare the time signatures of both chorus emissions and whistlers in order to determine how the spectral properties of these waves vary with position. In particular we determine differences in the frequency spectrum of the lightning-generated whistlers, both inside and outside the plasmasphere, and use these differences to test the hypothesis that whistlers propagating outside the plasmasphere are often strongly coupled to lower hybrid waves in regions where the plasma density profile is irregular. In the case of chorus emissions, we compare the frequency shifts of individual chorus elements as measured on the CLUSTER spacecraft and use this data to determine the spatial and temporal characteristics of the chorus source regions