Abstract
Abstract. Results of a statistical survey of F-region ion frictional heating are presented, a survey which is based on over 4000 h of common programme observations taken by the European incoherent scatter (EISCAT) UHF radar facility. The criterion adopted in this study for the identification of ion frictional heating was that defined by McCrea et al., requiring an enhancement in the F-region field-parallel ion temperature exceeding 100 K over two consecutive integration periods, which was itself based on a selection criterion for frictional heating derived for the study of high-latitude F-region ion temperature observations from the Atmospheric Explorer-C satellite. In the present study, the diurnal distribution of ion frictional heating observed by EISCAT is established and, furthermore, its dependence on geomagnetic activity and the orientation of the interplanetary magnetic field (IMF) is investigated; results are interpreted with reference to corresponding distributions of enhanced ion velocity, again derived from the extended set of EISCAT UHF common programme observations. The radar, due to its location relative to the large-scale convection pattern, observes ion frictional heating principally during the night, although preferentially during the post-midnight hours where there is reduced coupling between the ion and neutral populations. There is an increased preponderance of frictional heating during intervals of high geomagnetic activity and for a southward z component of the IMF and, moreover, evidence of asymmetries introduced by the y component of the IMF.
Highlights
A relative velocity between the ion and neutral populations in the F-region ionosphere results in an enhance-Correspondence to: J
The current study extends that documented by McCrea (1989) and McCrea et al (1991) in which the authors present the diurnal distribution of ion frictional heating, along with that of the related phenomena of enhanced ion velocity, derived statistically from F-region European incoherent scatter (EISCAT) common programme 1 (CP-1) and common programme 2 (CP-2) observations taken during 1985 and 1986
The selection criterion described in the previous section for the identi®cation of ion frictional heating was applied to the present extended data set of CP-1 and ®eld-aligned CP-2 observations of ®eld-parallel ion temperature at 312 km altitude
Summary
A relative velocity between the ion and neutral populations in the F-region ionosphere results in an enhance-. Davies ment in the temperature of the ions through frictional contact with the neutral atmosphere This mechanism is termed ion frictional heating and, at auroral latitudes where its occurrence was ®rst indicated by satellite observations, is a manifestation of the coupling between the ionosphere and magnetosphere. The ®rst experimental evidence indicating the existence of non-Maxwellian line-of-sight ion velocity distributions was provided by the Atmospheric Explorer-C satellite (St-Maurice et al, 1976) and their occurrence has subsequently been identi®ed from radar observations by the European incoherent scatter (EISCAT) radar (Lockwood et al, 1987; Moorcroft and Schlegel, 1988). The results of a statistical study of ion frictional heating are presented, a study which is based on over 4000 h of observations by the EISCAT UHF.
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