Ion heating in high-speed flow channel within the duskside cellof the polar cap ion convection under large IMF-By condition

摘要

F region strong sunward ion flow embedded in the duskside cell of expanding polarcap ion convection and coincidental increase in the ion temperature were observed fromabout 73° to 69° in geomagnetic latitude between 16:00 and 16:48 MLT on 19 August,2006 from an experiment using the European Incoherent Scatter (EISCAT) radars atTromso, Sodankyla and Longyearbyen together with the CUTLASS HF radars. Thespatiotemporal structure of the convection map obtained by the SuperDARN HF radarsshowed that the high-speed flow channel elongated in 14-17 MLT was movingequatorward. The flow channel appeared during an interval of negative interplanetarymagnetic field B, associated with large positive By. In order to evaluate ion frictionalheating and resultant ion temperature increase quantitatively, the experiment wasconducted to estimate the ion velocity vector and the ion temperature at the commonscattering volume of the EISCAT radars. While the flow channel moved equatorward, theion temperature increase became less evident at higher part of latitudes within the flowchannel, which means that ion frictional heating was depressed where the neutral gaseshad already responded to the high-speed ions. The increase in the ion temperature atparticular geomagnetic latitude continued for about 20 min, and then ceased while the ionvelocity was still enhanced. Ion frictional heating lasted until the neutral wind wasaccelerated to the equivalent level of the surrounded ion flow.