The researchers propose to continue studying the low- latitude ionosphere and thermosphere during magnetically quiet and disturbed periods. They will use the NCAR TGCM, our ionosphere model and satellite data in their effort to understand the basic processes that govern the behavior of these regions. The model predictions will be compared to available data in order to study the effects of winds, tides, and electric fields on the low latitude ionosphere. They will investigate the effects near the equator of the high latitude energy source, as occurs during a magnetic disturbance, as well as the presence of low latitude energy sources, such as neutral particle precipitation. The dynamics of the ionosphere and thermosphere are of interest since it is in this region (above 150 km altitude) that radio waves propagate for long distances for ground to ground communication, and for ground to satellite communication. The winds, tides and electric fields, have important effects on ionospheric structure and hence on the quality and reliability of such communication.