COOLING OF THE UPPER-ATMOSPHERE BY ENHANCED GREENHOUSE GASES - MODELING OF THERMOSPHERIC AND IONOSPHERIC EFFECTS

The concentrations of "greenhouse gases" - carbon dioxide and methane in particular - in the middle atmosphere are expected to double by the mid-21st century. This should lead to "global greenhouse cooling" of the upper atmosphere. Using the NCAR Thermosphere/Ionosphere General Circulation Model, we predict that (depending on location and the phase of the solar cycle) the thermospheric temperature will be lowered by 30-40 K and the air density at heights of 200-300 km will be reduced by 20-40%, thus increasing the orbital lifetimes of satellites. The height of the ionospheric F2-layer peak will drop on average by about 15 km, with some effect on radio propagation, though the F2-layer critical frequency will hardly be affected.