On the usefulness of &amp;lt;i&amp;gt;E&amp;lt;/i&amp;gt; region electron temperatures and lower &amp;lt;i&amp;gt;F&amp;lt;/i&amp;gt; region ion temperatures for the extraction of thermospheric parameters: a case study

J.-P. St.-Maurice,C. Cussenot,W. Kofman

doi:10.1007/s00585-999-1182-2

On the usefulness of &lt;i&gt;E&lt;/i&gt; region electron temperatures and lower &lt;i&gt;F&lt;/i&gt; region ion temperatures for the extraction of thermospheric parameters: a case study

J.-P. St.-Maurice, C. Cussenot + Show 1 more

Open Access

https://doi.org/10.1007/s00585-999-1182-2

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Abstract

Abstract. Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was particularly active geomagnetically. We have found that the E region electron temperatures responded quite predictably to the effective electric field. For this reason, the E region electron temperature correlated well with the lower F region ion temperature. However, there were several instances during the period under study when the magnitude of the E region electron temperature response was much larger than expected from the ion temperature observations at higher altitudes. We discovered that these instances were related to very strong neutral winds in the 110-175 km altitude region. In one instance that was scrutinized in detail using E region ion drift measurement in conjunction with the temperature observations, we uncovered that, as suspected, the wind was moving in a direction closely matching that of the ions, strongly suggesting that ion drag was at work. In this particular instance the wind reached a magnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 km altitude. Curiously enough, there was no indication of strong upper F region neutral winds at the time; this might have been because the event was uncovered around noon, at a time when, in the F region, the E×B drift was strongly westward but the pressure gradients strongly northward in the F region. Our study indicates that both the lower F region ion temperatures and the E region electron temperatures can be used to extract useful geophysical parameters such as the neutral density (through a determination of ion-neutral collision frequencies) and Joule heating rates (through the direct connection that we have confirmed exists between temperatures and the effective electric field).Key words. Ionosphere (auroral ionosphere; ionosphere atmosphere interactions; plasma temperature and density)

Highlights

It has been repeatedly pointed out that the ion temperature below 400 km altitude depends quadratically on the magnitude of the relative drift between ions and neutrals (e.g., Rees and Walker, 1968; St.-Maurice and Hanson, 1982, 1984)
Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was active geomagnetically
We have found that the E region electron temperatures responded quite predictably to the eective electric ®eld

Summary

Introduction

It has been repeatedly pointed out that the ion temperature below 400 km altitude depends quadratically on the magnitude of the relative drift between ions and neutrals (e.g., Rees and Walker, 1968; St.-Maurice and Hanson, 1982, 1984) It may not have been stressed strongly enough that this is equivalent to the ion temperature having a quadratic dependence on the magnitude of the eective electric ®eld. On the other hand, when the temperature enhancements are large, the ion velocity distribution becomes anisotropic and non-Maxwellian which complicates the analysis sometimes considerably. For these reasons, the ion temperatures may have been overlooked as a useful tool for monitoring the state of the thermosphere. With considerable progress made on data processing and analysis together with a much

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