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Results of a statistical survey of F-regionion frictional heating are presented, a survey which is based on over 4000 h ofcommon programme observations taken by the European incoherent scatter (EISCAT)UHF radar facility. The criterion adopted in this study for the identificationof ion frictional heating was that defined by McCrea <i>et al</i>., requiring anenhancement in the F-region field-parallel ion temperature exceeding 100 K overtwo consecutive integration periods, which was itself based on a selectioncriterion for frictional heating derived for the study of high-latitude F-regionion temperature observations from the Atmospheric Explorer-C satellite. In thepresent study, the diurnal distribution of ion frictional heating observed byEISCAT is established and, furthermore, its dependence on geomagnetic activityand the orientation of the interplanetary magnetic field (IMF) is investigated;results are interpreted with reference to corresponding distributions ofenhanced ion velocity, again derived from the extended set of EISCAT UHF commonprogramme observations. The radar, due to its location relative to thelarge-scale convection pattern, observes ion frictional heating principallyduring the night, although preferentially during the post-midnight hours wherethere is reduced coupling between the ion and neutral populations. There is anincreased preponderance of frictional heating during intervals of highgeomagnetic activity and for a southward z component of the IMF and, moreover,evidence of asymmetries introduced by the y component of the IMF

A statistical study of ion frictional heating observed by EISCAT