Electron temperatures during rapid subauroral ion drift events

R J Moffett,G J Bailey,L H Brace,A E Ennis,R A Heelis

doi:10.1007/s00585-998-0450-x

Abstract

Abstract. Examples of data from DE-2 satellite instruments are presented. These illustrate the behaviour of plasma parameters in the F-region and adjacent topside ionosphere during rapid sub-auroral ion drift (SAID) events. In particular, a variety of behaviours of the electron temperature (Te) is demonstrated, both within and equatorward of the SAID region. The Sheffield University plasmasphere-ionosphere model (SUPIM) is used to perform calculations in which a model SAID is applied to a plasma flux tube. The model results indicate that strongly elevated ion temperature (a recognised signature of SAID events) is on occasion sufficient to raise Te to observed values by ion-electron heat transfer. On other occasions, an additional heat source is required. It is suggested that such a source for the electron gas may be due to interaction between the ring current and the plasmasphere at high altitudes. The magnitude of the downward heat flux is consistent with that necessary to produce sub-auroral red arcs. The resulting strongly heated electron gas causes vibrational excitation of molecular nitrogen in the thermosphere. Key words. Electron temperature · Subauroral ion drift · Plasmasphere-ionosphere SUPIM

Highlights

Occurrences of a narrow band of rapid westward ion drift1) in the evening sector of the subauroral ionosphere were detected by instruments on board satellites
Using the observed ion drifts as inputs, mathematical models of the ionosphere have been used to study the causes of the observed signatures of sub-auroral ion drift (SAID) (Sellek et al, 1991, 1992; Moett et al, 1991, 1992a,b, 1993; KoÈroÈsmezey et al, 1992; Heelis et al, 1993)
For the results presented in Figs. 6±8, the equatorial heat source was turned on at the time of onset of the model SAID (15 min elapsed time) and switched o at 36 min elapsed time

Summary

Introduction

Occurrences of a narrow band of rapid westward ion drift (of order 1 km s)1) in the evening sector of the subauroral ionosphere were detected by instruments on board satellites. (1993), who investigated the temporal relationship between SAID and auroral substorms. A phenomenological model of SAID production, based on the ideas of Southwood and Wolf (1978) and Harel et al (1981), has been proposed by Anderson et al (1993) in order to account for the observed ionospheric signatures and their temporal relationship with substorms. Using the observed ion drifts as inputs, mathematical models of the ionosphere have been used to study the causes of the observed signatures of SAID (Sellek et al., 1991, 1992; Moett et al, 1991, 1992a,b, 1993; KoÈroÈsmezey et al, 1992; Heelis et al, 1993). Elevated and anisotropic ion temperatures, depletion of electron density, changes in ion composition, enhanced ®eldaligned plasmaows and the behaviour of H and He

Results

Discussion

Conclusion