JOVIAN DECAMETER EMISSIONS OBSERVED BY THE WIND WAVES RADIOASTRONOMY EXPERIMENT/

The WAVES radio astronomy experiment aboard the Wind spacecraft covers the frequency range from 1 MHz to 13.8 MHz with spectral resolution s ix times better than that of the Voyager PRA experiment. By combining Wind/WAVES observations with simultaneous observations made by the Nan cay Decametric Array (France) between 10 and 40 MHz, the entire freque ncy spectrum of the jovian decametric emission can be observed. Two re presentative Io-controlled events (Io-B/D and Io-C) have been selected and analysed in terms of the available models of the jovian environme nt. In the case of the Io-B/D event at frequencies below 20 MHz, obser vations and models, to some extent, may fit an emission beam aperture of about 87 degrees. To explain the higher frequencies we must assume that small refraction effects take place near the source region, consi stent with topside jovian ionospheric parameters deduced from previous direct measurements. The Io-C event cannot be explained with this sim ple emission beam geometry: additional effects have to be invoked, as strong propagation effects near caustics or large distortion of the ma gnetic field in the source.