CYCLOTRON DAMPING OF ION CYCLOTRON WHISTLERS: A METHOD FOR THE DETERMINATION OF ION TEMPERATURE.
IOWA UNIV IOWA CITY DEPT OF PHYSICS AND ASTRONOMY
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A method is presented of determining ion temperatures in the ionosphere from cyclotron damping of proton whistlers. For frequencies very close to the proton gyrofrequency in the long drawn-out tail of a proton whistlers, the amplitude of the proton whistler signal is observed to decrease very abruptly. It is shown that this abrupt cutoff is not due to temporal dispersion of the whistler energy nor due to the dependence of the wave amplitude on the local refractive index. Three effects, accessibility, collisional damping, and cyclotron damping, are investigated to explain the additional attenuation. For proton whistlers cyclotron damping is found to be the most important effect. A theoretical expression is derived for the attenuation of proton whistlers due to cyclotron damping. Using this theoretical expression a method is described for determining the temperature of protons in the plasma near the satellite from the duration of proton whistlers. Sample proton temperatures in the ionosphere are determined using VLF data from the Injun 3 and Alouette 1 satellites. These data are shown to be in good agreement with temperature measurements in the ionosphere by other experimenters. Author