The transition energy and the beaming angle of converted LO-mode waves from 100 to 400 kHz through density gradient according to observations of kilometric continuum radiations in the plasmapause

Abstract

The satellite observations such as the Cluster mission with four-point measurements show some local fluctuations in the density gradient in the vicinity of the plasmapause. These structures are found over a broad range of spatial scales, with a size from 20 to 5000 km. Also, the simultaneous observations of the kilometric continuum by IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) and GEOTAIL satellites have indicated another new evidence of a very broad emission. In this study, we considered the mode conversion of waves propagating under the presence of the density gradient in a scale length from 20 to 10,000 km, for a range of frequency from 100 to 400 kHz according to observations of the kilometric continuum. We calculated the transmitted energy flux as a function of the spatial scale lengths and the frequencies. We also calculated the resultant beaming angle for the frequency and the wave normal angle of incident waves. For these cases, results showed that the beaming angle becomes larger and smaller than the angle estimated by Jones' formula. We suggest that the spatial scale length should be less than about 100 km for the efficient mode conversion and then that the beaming angle becomes consistent with the observed the kilometric continuum.