Magnetospheric electron temperatures inferred from whistler dispersion measurements

Electron temperatures in the vicinity of the magnetospheric equator were estimated from dispersion measurements on 24 whistlers observed and digitally recorded at Halley, Antarctica (76 deg S, 27 deg W; L = 4.3) on 9 August 1989 between 1616 UT and 1707 UT, following a several-day period of moderately quiet geomagnetic conditions (Kp not greater than 2). The method previously described by Sazhin et al. (1990) was used with various models of electron density and temperature distribution along a field line, based on Park's (1972) DE-1 and DE-2 models. Uncertainties in the estimated temperatures were of the same order as the temperature values themselves, as result of small measurement errors in the whistler nose frequency and group time, and this limits the practical usefulness of the method, in its present state of development, as a diagnostic technique for inferring magnetospheric electron temperatures. In some cases, unphysical negative temperatures were obtained, probably as a consequence of an inaccurately assumed electron density distribution model; it was rarely the case with the DE-2 model for which the estimated temperature was approximately 1 eV, comparable with other estimates.

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