Theoretical model for the latitude dependence of the thermospheric annual and semiannual variations

A three-dimensional model for the annual and semiannual variations of the thermosphere is presented in which the energy and diffusive mass transport associated with global circulation are considered in a self-consistent form. It is shown that these processes play a major role in thermosphere dynamics and thus account for a number of temperature and composition phenomena such as (1) the helium and oxygen bulges in the winter hemispheres at lower altitudes, (2) the relatively large temperature variations (∼26%) in the annual component, which exceed by a factor of 3 those temperatures inferred from the satellite drag data and would be much too large for a thermosphere in diffusive equilibrium, (3) the 7% variation of the exospheric temperature at the poles in the latitude dependent semiannual component associated there with a significant depletion of oxygen and helium during the equinox, and (4) the nearly height independent and relatively small amplitudes in the total mass density of the latitude dependent components that are responsible for the fact that the latitude variations of the semiannual effect have so far eluded observations from satellite drag data and that the globally uniform component of the semiannual effect appears to be relatively strong in comparison with the annual variations.