Global circulation and temperature structure of thermosphere with high‐latitude plasma convection

This paper examines the effect of magnetospheric convection in modifying the diurnal neutral gas temperature distribution and circulation of the thermosphere for equinox conditions, using NCAR's thermospheric general circulation model. Numerical experiments are presented to illustrate the differences in temperature structure and circulation due to (1) solar heating alone, (2) solar heating plus plasma convection with coincident geographic and geomagnetic poles, and (3) solar heating plus plasma convection with displaced poles. The high‐latitude plasma convection has an important influence on the global thermospheric structure and circulation. Plasma convection with displaced poles introduces a universal time dependence to the circulation and temperature structure; similar patterns occur in the northern and southern hemisphere, with a 12‐hour time difference. Magnetospheric convection drives a largely rotational, nondivergent, double‐vortex wind system at F region altitudes that can attain velocities greater than 500 m s−1 during moderate levels of geomagnetic activity. These vortices extend downward into the lower thermosphere. However, the cold low‐pressure cyclonic circulation near the dawn terminator is much more pronounced than the warm high‐pressure anticyclonic circulation in the evening sector.