On the feasibility of developing a global atmospheric model extending from the ground to the exosphere

It is well known that solar EUV and UV forcing and auroral heat and momentum sources have a significant effect on thermospheric and ionospheric structure and dynamics. Yet the observed variability in these regions appears to be more than can be accounted for by considering only these processes. It is also known that the upward propagating diurnal and semi-diurnal tides affect the thermosphere and ionosphere and there are also studies that show that large scale planetary waves, such as the Quasi-two day wave, and 5 and 15 day waves produce signals as high as the ionospheric F-region. Furthermore, planetary wave and gravity wave breaking in the mesosphere has been shown to affect the stratosphere through "downward control." Most models of the middle atmosphere have their upper boundary in the 70-150 km region whereas most models of the thermosphere/ionosphere have their lower boundary near 80-95 km. This region of the atmosphere is highly dynamic making the specifications of thermal, compositional, dynamical and electrodynamical boundary conditions difficult. There is an important need for the development of a model of the entire atmosphere that can be used to investigate couplings between atmospheric regions and solar-terrestrial interactions. A crude attempt has been made to develop such a model by coupling the NCAR Community Climate Model (CCM3) and the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). This coupled model has been run for two years and the findings from this simulation indicate that important couplings between atmospheric regions occur. These results suggest that a model of the entire atmosphere is feasible and it will be needed to address many of the important problems that will arise in the new millenium.