Association of kilometric continuum radiation with plasmaspheric structures

James L. Green, Scott Boardsen, Shing F. Fung, H. Matsumoto, K. Hashimoto, 
R.R. Anderson, B.R. Sandel, B.W. Reinisch


A year's worth of observations of kilometric continuum (KC) from the plasma wave
instrument (PWI) on GEOTAIL and extreme ultraviolet (EUV) images of the
plasmasphere from IMAGE are compared. In the vast majority (~94%) of the 87
cases when simultaneous data from both spacecraft were available, KC was
observed to be associated with density depletions or notch structures in the
plasmasphere. From a careful analysis of 1 month of EUV data comprising 13 notch
structures, only one notch structure was found in which no accompanying KC was
observed when GEOTAIL was in a low-latitude position and therefore should have
observed the emission if it were generated. IMAGE observations from the radio
plasma imager (RPI) during passage through a plasmaspheric notch structure found
that KC was generated in or very near the magnetic equator at steep gradients in
density and associated with emissions in the upper hybrid resonance band as
previously reported by others at lower frequencies. Statistical analysis of the
KC events associated with plasmaspheric notch structures shows that the typical
source region is at an equatorial radial distance of ~2.4 RE (Earth radii) in
the magnetic equator and produces an emission cone that is ~40 degrees in
longitude and ~20 degrees in latitude. These results show that a density
depletion or notch structure in the plasmasphere is typically a critical
condition for the generation of KC but that the notch structures do not always
provide the conditions necessary for the generation of the emission. 


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Journal of Geophysical Research, 109, A03203, doi:10.1029/2003JA010093, 2004