On the origin of whistler mode radiation in the plasmasphere

James L. Green, Scott Boardsen, Leonard Garcia, W. W. L. Taylor, Shing F. Fung, 
and B. W. Reinisch


The origin of whistler mode radiation in the plasmasphere is examined from 3
years of plasma wave observations from the Dynamics Explorer and the Imager for
Magnetopauseto- Aurora Global Exploration spacecraft. These data are used to
construct plasma wave intensity maps of whistler mode radiation in the
plasmasphere. The highest average intensities of the radiation in the wave maps
show source locations and/or sites of wave amplification. Each type of wave is
classified on the basis of its magnetic latitude and longitude rather than any
spectral feature. Equatorial electromagnetic (EM) emissions ( 30Ð330 Hz),
plasmaspheric hiss ( 330 Hz to 3.3 kHz), chorus ( 2Ð6 kHz), and VLF transmitters
( 10Ð50 kHz) are the main types of waves that are clearly delineated in the
plasma wave maps. Observations of the equatorial EM emissions show that the most
intense region is on or near the magnetic equator in the afternoon sector and
that during times of negative Bz (interplanetary magnetic field) the maximum
intensity moves from L values of 3 to <2. These observations are consistent with
the origin of this emission being particle-wave interactions in or near the
magnetic equator. Plasmaspheric hiss shows high intensity at high latitudes and
low altitudes (L shells from 2 to 4) and in the magnetic equator with L values
from 2 to 3 in the early afternoon sector. The longitudinal distribution of the
hiss intensity (excluding the enhancement at the equator) is similar to the
distribution of lightning: stronger over continents than over the ocean,
stronger in the summer than in the winter, and stronger on the dayside than on
the nightside. These observations strongly support lightning as the dominant
source for plasmaspheric hiss, which, through particle-wave interactions,
maintains the slot region in the radiation belts. The enhancement of hiss at the
magnetic equator is consistent with particle-wave interactions. The chorus
emissions are most intense on the morningside as previously reported. At
frequencies from  10 to  50 kHz, VLF transmitters dominate the spectrum. The
maximum intensity of the VLF transmitters is in the late evening or early
morning with enhancements all along L shells from 1.8 to 3.

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Journal of Geophysical Research, 110, A03201, doi:10.1029/2004JA010495, 2005