| Vol. 27, Issue 2 |
Mars orbiter Planet-B, which was launched in July 1998, observed the dusk side of the terrestrial plasmasphere while it was in a 6-month parking orbit around Earth. This orbit provided an opportunity to image the plasmasphere from the outside for the first time. Nakamura et al. [141] discuss results of this plasmaspheric imaging that was captured by the extreme ultraviolet scanner on board Planet-B. While the goal of the scanner was to detect Martian helium gas and ions, the scanner detected interplanetary helium emissions as well as those from the terrestrial plasmasphere. Franz et al. [169] use electric field data from the Polar Plasma Wave Instrument to study the perpendicular scale of electron phase-space holes (small-scale electrostatic structure that are everywhere in space and are fundamental to certain wave-particle interactions). They show that the holes are nearly spherical when the ratio of electron cyclotron frequency to plasma frequency is greater than 1 and that the holes become oblate with decreasing values of this ratio. The authors propose a scaling argument based on electron gyrokinetic theory to build a simple model that agrees with observations. Eack et al. [185] suggest that thunderstorms may be producing gamma rays. The authors launched balloon-borne gamma-ray and electric-field-change instruments into a thunderstorm in Oklahoma in June 1998 and found that during the descent through a thunderstorm anvil, where a strong electric field appeared to be present, the instruments registered a large increase in the gamma-ray flux. The authors postulate that the increase is due to an electric field in the anvil of the thunderstorm. Also in this issue, Beasley et al. [189] report on their observations of electric-field changes at altitudes of thunderstorms and attribute the changes to lightning. Deploying several balloon-borne electric-field-change antennae in storms during 1998, they conclude that the observed field changes result from charge motion relatively near the balloon and are possibly associated with distant ground flashes. |
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