
%0 Journal Article
%A Melrose, DB 
%T The Mechanism Responsible for 'Shadow' Type III Solar Radio Bursts. I. Absorption due to Langmuir Turbulence
%J Australian Journal of Physics
%D 1974/04/01
%V 27
%N 2
%P 259-270
%K 
%R https://doi.org/10.1071/PH740259
%U https://www.publish.csiro.au/paper/PH740259 
%X The hypothesis is advanced that for 'shadow' type III solar radio events (absorption features with drift rates and bandwidths typical of type III bursts or U-bursts) the absorption mechanism involves Langmuir turbulence, such absorption being the inverse of either fundamental (I = J;,) or second harmonic (f = 2/p) plasma emission. The theory for both absorption processes is developed and applied to shadow type III events with the following results: (1) the predicted absorption is confined to a very narrow frequency range (fl.I/ I ~ 10- 3); (2) effective absorption requires an energy density in Langmuir turbulence (with phase speeds ~tc) in excess of 10-9 ergcm- 3 for the fundamental and in excess of 3 x 10-6 ergcm- 3 for the second harmonic; (3) the brightness of the background source must exceed 109 and 1016 K for absorption at the fundamental and second harmonic respectively. Comparison of the theory with the properties of an event discussed by Kai (1973) leads to the conclusions: (1) absorption at the second harmonic is unacceptable because of the high brightness temperature required; (2) to explain the observed bandwidth in terms of absorption at the fundamental, the absorbing region and the background source must overlap in height; (3) to explain the observed reduction in brightness temperature requires that the initial brightness temperature exceed 5·5 X 109 K (the observed value was 109 K). 
