Propagation of auroral hiss at high altitudes -: art. no. 1481

[1] Using multicomponent wave measurements of the Polar spacecraft, we provide direct evidence of the propagation pattern of funnel-shaped auroral hiss at a radial distance of 5 Earth radii. The waves propagate upward and the Poynting flux is directed toward higher latitudes in the high-latitude part of the emission and to lower latitudes in the low-latitude part. The wave vectors are found to be close to the whistler mode resonance angle. Consistent with the theory, the latitudinal component of the wave vector is opposite compared to that of the Poynting flux in the low-latitude and high-latitude parts of the funnel-shaped emission. In the central part of the emission we observe a very broad distribution of the wave energy with respect to the azimuth angle. The waves thus simultaneously come from different directions with different wave vectors. This leads us to the conclusion that hiss is more likely generated in an extended sheet source rather than in a vertical line source or a point source. In this case the observed propagation pattern suggests that the sheet source is oriented roughly in the longitudinal direction, consistent with the region where we can expect presence of upgoing or counterstreaming electron beams.