On the usefulness of E region electron temperatures and lower F region ion temperatures for the extraction of thermospheric parameters: a case study

[摘要] Using EISCAT data, we have studied thebehavior of the E region electron temperature and of the lower Fregion ion temperature during a period that was particularly activegeomagnetically. We have found that the E region electron temperaturesresponded quite predictably to the effective electric field. For this reason,the E region electron temperature correlated well with the lower Fregion ion temperature. However, there were several instances during the periodunder study when the magnitude of the E region electron temperatureresponse was much larger than expected from the ion temperature observations athigher altitudes. We discovered that these instances were related to very strongneutral winds in the 110-175 km altitude region. In one instance that wasscrutinized in detail using E region ion drift measurement in conjunctionwith the temperature observations, we uncovered that, as suspected, the wind wasmoving in a direction closely matching that of the ions, strongly suggestingthat ion drag was at work. In this particular instance the wind reached amagnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 kmaltitude. Curiously enough, there was no indication of strong upper Fregion neutral winds at the time; this might have been because the event wasuncovered around noon, at a time when, in the F region, the E×Bdrift was strongly westward but the pressure gradients strongly northward in theF region. Our study indicates that both the lower F region iontemperatures and the E region electron temperatures can be used toextract useful geophysical parameters such as the neutral density (through adetermination of ion-neutral collision frequencies) and Joule heating rates(through the direct connection that we have confirmed exists betweentemperatures and the effective electric field).

Key words. Ionosphere (auroral ionosphere; ionosphereatmosphere interactions; plasma temperature and density)

[学科分类] 地球科学(综合)