Abstract
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.
Highlights
Electric fields and particle precipitation can strongly alter the state of the upper atmosphere, most notably in the polar regions
The results presented in this paper have demonstrated a
As better coordination between complementary iono- rapid and local thermospheric response to ionospheric forcspheric and thermospheric experiments reveals the details of ing which challenges the accepted view of the thermosphere ion-neutral coupling and improved instrumentation delivers as a relatively viscous and slow-moving sink of energy dibetter spatial and temporal resolution it should be possible rected into the region through magnetosphere-ionosphere to parameterise the local and rapid response of the thermo- coupling
Summary
Electric fields and particle precipitation can strongly alter the state of the upper atmosphere, most notably in the polar regions. Heelis et al (2002) have used a 6 day time series of ion and neutral parameters, together with the relevant time series of IMF conditions, to derive response times for the ionosphere and thermosphere to changes in solar forcing. The paucity of relevant experiments and difficulty in attributing reasonable estimates of errors and together with other factors has resulted in a lack of consensus as to the most reliable figures. Combining this instrumentation, in this paper we investigate the rapid and local thermospheric response to ionospheric forcing, the driving mechanism behind the observed thermospheric features and the implications for modelling the coupled ionosphere and thermosphere
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