Transport processes in the thermosphere.

Description of two different approaches which have been undertaken to consider horizontal transport in the upper atmosphere by large-scale circulation. First and most direct, the horizontal wind field in the middle and upper thermosphere was calculated based on the pressure distributions derived from satellite orbital decay observations. The continuity conditions were used to calculate the vertical motions. The second approach was to evaluate the energy deficits or surpluses as a function of altitude and latitude and to assume the presence of vertical motions sufficient to balance these deficits or surpluses by compressional heating or cooling. Then continuity conditions were used to derive horizontal winds. The results of the two approaches are compatible, and are largely complementary. Downward velocities are near 1 m/sec at 300 km over the diurnal minimum and the winter polar region, and 1 cm/sec at 100 km over the winter polar region.