Upper thermospheric ion-neutral coupling from combined optical and radar experiments over Svalbard

Abstract. The response of thermospheric neutral parameters such as winds and temperatures to rapid changes in geophysical conditions has usually been considered to be relatively slow, on the order of hours, and steady, representing an integration of more rapid ionospheric changes. Quantifying the relevant ion-neutral coupling has proved difficult due to a lack of relevant laboratory data for the most important collisions, namely between neutral atomic oxygen and its first ion. As a result the representation of ion-neutral coupling in numerical models of the upper atmosphere has often produced poor comparison to experimental data. Using a unique combination of spatially extended ion and neutral thermospheric parameters we show that the neutral response can be very rapid, within 15 min, to imposed forcing via ion-neutral coupling. The array of complementary instrumentation measuring the thermosphere above Svalbard in the Northern Hemisphere allows detailed study of the causes and effects from both the ion and neutral perspectives. The implications for development and testing of the thermospheric numerical models is discussed.