Global energy deposition to the topside ionosphere from superthermal electrons G.V. Khazanov a , M.W. Liemohn b, *, J.U. Kozyra b , D.L. Gallagher c a Geophysical Institute and Physics Department, University of Alaska Fairbanks, Fairbanks, AK 99775, USA b Department of Atmospheric, Oceanic and Space Sciences, Space Physics Research Laboratory, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, USA c Space Sciences Laboratory, NASA Marshall Space Flight Center, Huntsville, AL 35812, USA Received 12 August 1999; accepted 20 October 1999 Abstract The subauroral heat input to the topside ionosphere from two superthermal electron sources, photoelectrons and plasma sheet electrons, are calculated using a global kinetic model of electron transport in the inner magnetosphere. Peak rates above 10 10 eV cm 2 s 1 are found for photoelectrons in the midlatitude afternoon region, while the peak deposition rate for plasma sheet electrons only occasionally approaches 10 9 eV cm 2 s 1 , and is typically con®ned to the morningside. Trapped clouds of plasma sheet electrons, however, are shown to have lasting eects on the structure of topside heat input, as the energetic electrons corotate and slowly transfer their energy to the thermal plasma over a course of days. These energy inputs are compared with other heat sources in the inner magnetosphere. It is concluded that, while other processes can inject large amounts of energy into the ionosphere in spatially and temporally localized regions, photoelectrons are the strongest and steadiest heat source into the topside ionosphere. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Topside ionosphere; Superthermal electrons; Heating 1. Introduction Energy deposition to the thermal plasma in the inner magnetosphere is a vital contributor to the global energy balance of the ionosphere±magnetosphere sys- tem. For instance, knowledge of the energy precipi- tation from the magnetosphere into the ionosphere and thermosphere is crucially important for accurate ionospheric prediction. Incorporation of deterministic values of these quantities is a necessary input to any large-scale circulation model. Energy transferred to the thermal plasma in the near-Earth region is conducted down the ®eld lines into the topside ionosphere, where it modi®es the thermal, compositional, and optical structures there (Chandler et al., 1988; Kozyra et al., 1990; Comfort et al., 1995). The development of an improved modeling capability for ionospheric speci®ca- tion and prediction requires detailed knowledge of this heat input into the upper atmosphere. In the next mil- lennium, we will see an even greater reliance on satel- lite communications and radio navigation, necessitating greater accuracy from the current batch Journal of Atmospheric and Solar-Terrestrial Physics 62 (2000) 947±954 1364-6826/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S1364-6826(00)00033-X * Corresponding author. Tel.: +1-734-763-6229; fax: +1- 734-647-3083. E-mail address: liemohn@engin.umich.edu (M.W. Lie- mohn).