Distributions of Plasmaspheric Plasma Waves

J. Green (NASA Goddard Space Flight Center, Greenbelt, MD 20771), S. Boardsen, 
S. Fung, L. Garcia, and B. Reinisch

The plasmasphere is a high-density region of cold plasma around the earth
residing on closed field lines. The high electron densities support trapped
whistler mode radiation.  It is well known that the distribution of
high-energy radiation-belt electrons within the plasmasphere is modified by
their interactions with whistler mode waves in addition to radial diffusion. 
We demonstrate that the plasmaspheric whistler mode spectrum consists of four
major emissions: electromagnetic (EM) equatorial radiation, plasmaspheric
hiss, chorus, and emissions from ground-based transmitters.  Plasma wave maps
(spatial distribution of average wave intensities) from the IMAGE and DE-1
plasma wave instruments will be used to study the origin of these emissions.
Observations of EM equatorial emissions in the low-frequency spectrum (10 -
300 Hz) show that the most intense region is in or near the magnetic equator
in the afternoon sector and that during times of negative IMF Bz that maximum
intensity moves from L values of 3 to less than 2. These observations are
consistent with particle-wave interactions in or near the magnetic equator.
Chorus emissions (300 Hz - 12.5 kHz) are observed in the outer portions of
the plasmasphere and are associated with disturbed times and are believed to
be responsible for energetic electron precipitation on closed field lines in
the subauroral regions. Plasmaspheric hiss (300 Hz - 3.3 kHz) shows the
peak-intensity regions both at high latitudes near L= 4 and in the magnetic
equator in the L = 2 to 3 range.  The longitudinal distribution of the
average intensity of plasmaspheric hiss peaks near late afternoon with the
minimum near early morning local times. Although the generation of
plasmaspheric hiss is controversial the observations presented here points to
lightning, which has a similar local-time distribution, as a major
contributor to the hiss emission spectrum. At frequencies from ~10 - 50 kHz
whistler mode emissions from ground-based transmitters are also observed. 
For these emissions the maximum intensity shifts almost exclusively to the
local evening with enhancements along all L shells from 1.8 to 3. Indications
are that the cyclotron resonance also operates in this frequency range.  
This paper will discuss new results on the distribution of plasma waves in
the plasmasphere and their origin. 

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions,
3 - 6 February 2004, Yosemite, California, USA