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G. Thejappa (University of Maryland, College Park), R. J. MacDowall (NASA, Goddard Space Flight Center)
We present simultaneous observations of an interplanetary type II radio burst and a pair of type III radio bursts by the Ulysses and Wind spacecraft separated by more than 100 degrees in heliographic longitude. To explain the widespread visibility of these radio emissions, we have developed a computer program to trace the rays in the solar wind plasma with or without random density fluctuations. The computations show that the refraction causes the fundamental and harmonic emissions to be directive by focussing them into narrow and wide cones, respectively. In our Monte Carlo simulation code, we sample the polar and azimuthal angles of the direction of the ray following scattering and path length between scattering events using probability distributions. The computed type III burst directivities appear to agree very well with observations in comparison with those obtained using the previous methods. The directivity calculations indicate that type II and type III bursts detected simultaneously by the widely separated Ulysses and Wind spacecraft are probably emitted at the second harmonic of the electron plasma frequency.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.