Interactions between the polar ionosphere and thermosphere

The temperature, composition and circulation of the ionosphere and thermosphere in the polar regions are closely coupled and display a marked variation with altitude, latitude, longitude, universal time, season, solar cycle, and geomagnetic activity. To a large degree, this variation is a consequence of the effect that magnetospheric electric fields, particle precipitation, and heat flows have on the ionosphere-thermosphere system. These magnetospheric processes act to produce ionospheric hot spots, plasma blobs, localized ionization troughs, extended tongues of ionization and ion composition changes. These ionospheric features then affect the thermosphere because of ion-neutral momentum and energy coupling. The resulting interactions act to modify the thermospheric circulation, composition, and temperature, and this, in turn, affects the ionosphere. However, there are significant time delays associated with the various interactions. These and other results are reviewed.