Intensity Distribution of Plasmaspheric Hiss in the Plasmasphere

Scott Boardsen (1), James Green (2), Shing Fung (2), Leonard Garcia (3), 
and Bodo Reinisch (4)

(1) L3 Communications, Largo, MD, 20771
(2) NASA Goddard Space Flight Center, Greenbelt, MD 20771 
(3) QSS Group, Inc.
(4) Center for Atmospheric Research, Univ. of Mass. Lowell, Lowell, MA 01854 


Plasmaspheric hiss is an electromagnetic emission in the 10s Hz to ~10 kHz
frequency range propagating in the whistler mode that is typically confined
within the plasmasphere.  Two of the most important aspects about
plasmaspheric hiss are its source location and generation mechanism.
Generation mechanisms have been proposed both inside and outside the
plasmasphere and are still controversial.  To investigate the source
location, plasma wave intensity maps have been constructed by using five
years of plasma wave observations from the Dynamics Explorer and three years
from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE)
spacecraft. These intensity maps show the potential source locations or
sites where waves are amplified due to particle-wave interactions. In this
presentation, we show that the plasmaspheric hiss spectrum can be viewed as
having low (10 Ð 300 Hz), mid (300 Hz Ð 3.3 kHz), and high frequency (> 3.3
kHz) components.  Observations of low-frequency plasmaspheric hiss show that
the most intense region is in or near the magnetic equator in the afternoon
sector and that the maximum intensity region tends to move from L value of 3
to less than 2 during times of negative Bz. These observations are
consistent with particle-wave interactions in or near the magnetic equator.
The mid-frequency portion of the hiss spectrum shows the peak-intensity
region moves from  high latitudes at L= 4 toward the magnetic equator over L
= 2 to 3.  The longitudinal distribution of the hiss intensity in this
frequency range is similar to that of lightning intensity with the peak near
late afternoon and the minimum near early morning local times.  The
near-equatorial minimum at L=2-3 is also consistent with particle-wave
interactions in the magnetic equator.  At frequencies above 3.3 kHz the
maximum intensity shifts to the local evening-post midnight with
enhancements along all L shells from 1.8 to 3.   Indications are that the
cyclotron resonance also operates in this frequency range.  

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003