Analysis of 'Christmas Tree' radiation patterns seen in Kilometric Continuum detected by RPI on the IMAGE spacecraft

The Radio Plasma Imager (RPI) on the IMAGE spacecraft frequently detects radiation patterns in the Kilometric Continuum frequency range from 100 kHz to 500 kHz as it crosses the magnetic equator. These radiation patterns often take on a 'Christmas tree' like appearance in frequency-time spectrograms, with the lower frequency components more spread out in magnetic latitude about the equator than that of the higher frequency components. Some of these patterns have a hollowed out appearance with the radiation intensity diminishing around the magnetic equator consistent with off equatorial beaming from the source, while others do not show such a diminishing in intensity around the equator. One possible explanation of this radiation pattern is a very sharp plasmapause coupled with off equatorial beam angle that is dependent upon the ratio of fce/fpe as predicted by many theories. Some of these patterns appear to be qualitatively consistent with theories like linear mode conversion that predict of equatorial beaming, while other patterns seem to be inconsistent. Along will a statistical analysis of the observations, we will present a ray tracing analysis to investigate how well we can quantitatively reconstruct these radiations patterns by adjusting the shape of the plasmapause and assuming linear mode conversion at the source.