Propagation analysis of plasmaspheric hiss using Polar PWI measurements

We have analyzed high-rate waveform data, taken by the POLAR Plasma Wave In strument at high altitudes in the equatorial plasmasphere, to study plasmas pheric hiss in the range of frequencies between 100 Hz and several kHz. The se emissions are found almost everywhere in the plasmasphere, and their ori gin is still controversial. Our analysis of several cases shows that most o f the waves were propagating more or less parallel to the Earth's magnetic field, but sometimes a few of them were propagating obliquely with their no rmals near the Gendrin angle. Evidence of amplification was found near the geomagnetic equator. The results suggest that waves with normals both paral lel and anti-parallel to the magnetic field were being amplified by the cla ssical mechanism that involves gyroresonant interaction with energetic elec trons.