Solar cycle variability in mean thermospheric composition and temperature induced by atmospheric tides

Abstract

AbstractIn this paper we demonstrate that dissipation of upward propagating tides produces significant changes in the mean temperature of the thermosphere, ranging from +19 K at solar minimum to −15 K at solar maximum in the equatorial region. Our methodology consists of measuring the differential response of the thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) under solar minimum and solar maximum conditions to constant tidal forcing at its 97 km lower boundary, as specified by the observationally based Climatological Tidal Model of the Thermosphere. Diagnosis of the model reveals that these changes are mainly driven by 5.3 μm nitric oxide (NO) cooling, which more efficiently cools the thermosphere at solar maximum. The main role of the tides is to modify the mean molecular oxygen densities ([O2]) through tidal‐induced advective transport, which then lead to changes in NO densities through oxygen‐nitrogen chemistry. Through tidal‐induced changes in temperature and O, O2, and N2 densities, effects on the ionosphere are also quite substantial; tidal‐induced modifications to zonal‐mean F region peak electron densities (NmF2) are of order −10% at solar maximum and −30% at solar minimum in the equatorial region. Our results introduce an additional consideration when attributing long‐term changes in thermospheric temperature and electron densities to CO2 cooling effects alone; that is, dissipation of upward propagating tides may constitute an additional element of global change in the ionosphere‐thermosphere (IT) system.