Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm14b..04g&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM14B-04
Physics
2716 Energetic Particles: Precipitating, 2730 Magnetosphere: Inner, 2774 Radiation Belts, 6939 Magnetospheric Physics (2700), 6964 Radio Wave Propagation
Scientific paper
The radiation belt slot region is known to result from losses of energetic electrons by enhanced pitch-angle scattering by whislter mode waves associated with plasmaspheric hiss emission. The distributions of whistler mode waves in the slot L range are therefore important for understanding the electron radiation belt. The sources and distributions of the waves are, however, still controversial. In the present study, using the Akebono/MCA data [1989-2005] and the IMAGE/RPI data [2000-2005], we have constructed the average plasmaspheric hiss spectral distributions over a broad frequency range. In addition, we have investigated the spatial distributions of plasmaspheric hiss with the wave map technique [Green et al.(2005)]. Our study shows that the broadband plasmaspheric hiss are distributed in the frequency range of 100Hz to several kHz, and exhibit a broad intensive peak. The frequency of the intensity peak tends to increase with magnetic latitude. The frequencies of the most intense waves in the nominal slot L range (2-50nT) are found to be between 300Hz and 600Hz on average. During high storm activity (Dst <-150nT), however, the peak frequencies become slightly lower. The intensity of plasmaspheric hiss clearly depends on substorm activity as measured by the AE index, consistent with Meredith et al.(2004). The hiss wave intensity maps also show a strong local time asymmetry. The large amplitude waves are observed at 6:00-19:00 MLT. From our extensive analysis, we have also found an L dependence of hiss activity, with the larger amplitude waves being observed at lower L during substorm active conditions. The same tendency can be found for solar activity. The average intensities of the waves during 1989-1991 and 2000-2001 are a few dB larger than those during 1992-1997 and 2005. The most intense waves are observed at lower L during high solar activity. The statistical study on spectrum features of the plasmaspheric hiss together with the spatial distribution show clear dependences of storm, substorm and solar activities. Acknowledgments: The authors wish to thank Akebono/VLF members for their contribution to the VLF instrument and its data analyses. The authors also wish to thank B. W. Reinisch and CDAWeb for providing the IMAGE/RPI dynamic spectrogram data. References: Green, J. L., S. Boardsen, L. Garcia, W. W. L. Taylor, S. F. Fung, and B. W. Reinisch (2005), On the origin of whistler mode radiation in the plasmasphere, J. Geophys. Res., 110, A03201, doi:10.1029/2004JA010495. Meredith, N. P., R. B. Horne, R. M. Thorne, D. Summers, and R. R. Anderson (2004), Substorm dependence of plasmaspheric hiss, J. Geophys. Res., 109, A06209, doi:10.1029/2004JA010387.
Fung Shing F.
Goto Yasuhiro
Kasahara Yasushi
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