Postsunset vortex in equatorial F-region plasma drifts and implications for bottomside spread-F

Abstract

Recent high‐resolution incoherent scatter drift measurements conducted at Jicamarca during solar minimum conditions indicate that a vortical plasma flow pattern accompanies the well known prereversal enhancement events observed in the equatorial F region. The vortex is centered at ∼250 km altitude and about 2000–3000 km east of the evening terminator and is characterized by upward and downward flows to the west and to the east and eastward and westward flows on the top and the bottom, respectively. Postsunset bottomside spread‐F events are observed to commence in the interior of the vortex in regions of westward plasma drifts. The formation of the vortex implies localized charging of the postsunset bottomside F region in response to eastward neutral wind driven F region dynamo action.