On the Origin of Kilometric Continuum

James L. Green, B. R. Sandel, Shing F. Fung, D. L. Gallagher, and B. W. Reinisch


The Radio Plasma Imager (RPI) and the Extreme Ultraviolet (EUV) Imager instruments 
on the polar orbiting IMAGE satellite are providing new observations of the source 
region of kilometric continuum. Observations by the IMAGE instruments are now able 
to clarify some aspects of the source of this emission and put some previous 
observations into a new perspective. The IMAGE observations show that kilometric 
continuum is generated at the plasmapause, from sources in or very near the 
magnetic equator, within a bite-out region of the plasmasphere. It is not known if 
the bite-out region is a necessary condition for the generation of kilometric 
continuum. From ray tracing calculations in a model plasmasphere having a bite-out 
feature, it is found that a kilometric continuum source can produce a relatively 
narrow emission cone that is largely confined to the longitudinal extent of the 
bite-out structure. Since the bite-out structure is observed to co-rotate with the 
plasmasphere so would the beamed kilometric continuum. In addition, the observed 
narrow latitudinal extent of the emission cone does not appear to be a propagation 
effect but is perhaps produced by the emission mechanism, such as the linear or 
nonlinear mode-conversion processes at the upper hybrid resonance proposed by a 
number of investigators.  The processes by which bite-out structures are produced 
in the plasmasphere are not completely understood at this time. 

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Accepted for publication in Journal of Geophysical Research, 2002