Ionosphere and Thermosphere Coupling at Mid- and Subauroral Latitudes

This chapter addresses the ionosphere–thermosphere (I/T) coupling phenomena. We define I/T coupling as the dynamical interaction between plasma and neutral particles in the upper atmosphere. This interaction involves the ionosphere response to changes in the thermospheric wind, composition, and temperature, and how the thermosphere dynamics and thermal state are affected by plasma electrodynamics, which may well be under the influence of magnetosphere–ionosphere coupling. It has been the main research focus for decades and will continue to be the center of aeronomy study. The ultimate sources driving dynamical I/T variations may be classified into origins from “above” (the sun, interplanetary, and magnetosphere) and from “below” (the low atmosphere, solid earth surface, and beneath). The cause-effect pathways have been presented in many previous studies covering broad research topics. here we provide only a few I/T coupling phenomena with a focus primarily on mid- and subauroral latitude processes to demonstrate recent progress and new understanding in several research frontiers. Topics covered include specifically ionospheric longitudinal variation morphology (from continental to global scales); neutral wind (especially zonal wind) effects on ionospheric longitudinal variations; important processes for the summer nighttime ionosphere; typical stormtime I/T coupling processes; high latitude winds; and stormtime subauroral I/T coupling phenomena.