STATISTICAL IMAGING OF THE VENUS FORESHOCK USING VLF WAVE EMISSIONS

Strong VLF wave emissions have been shown to be an intrinsic property of the Venus foreshock and foreshocks in general. In this work, we use these measured wave emissions to construct statistical ''images'' of the Venus foreshock. This analysis method allows us to develop a macro scopic picture of the wave properties, the inferred particle distribut ions, and their evolution as a function of position within the foresho ck as well as compare our observations to Earth. The electron foreshoc k emissions at Venus are parallel polarized Langmuir mode waves with t he same peak amplitude at the foreshock boundary as terrestrial emissi ons (10 mV/m). However, the wave characteristics differ markedly betwe en the upstream and downstream foreshocks for near Parker spiral inter planetary magnetic field (IMF) orientations (similar to 35 degrees for Venus). Additionally, there is a dramatic decrease in wave intensity for distances beyond similar to 15 R-v from the point of tangency alon g the foreshock boundary. These characteristics in the wave emissions provide strong observational evidence supporting reflection and energi zation of solar wind electrons at the shock as the dominant source for providing upstream electrons, not leakage. In the ion foreshock the w ave emissions consist of parallel polarized ion acoustic-like waves wi th similar intensities and spectral characteristics to terrestrial emi ssions. However, these waves are situated much deeper in the foreshock than expected from terrestrial observations. Surprisingly, no emissio ns are observed in regions where field aligned ion distributions are e xpected. Rather, the emissions are confined to a region where diffuse ion distributions are expected.