Meridional Circulation in the Thermosphere I. Equinox Conditions

Abstract

The mean meridional circulation and latitudinal variation of temperature in the thermosphere are considered for equinox conditions. With regard to these parameters there have been serious discrepancies between observational indications and theoretical expectations. A numerical model of the zonally symmetric thermospheric circulation is formulated and solved using a finite-difference initial value approach to steady-state solutions. Solutions are obtained for three different prescriptions of forcing terms: solar heating alone, solar heating plus an effective momentum source due to diurnal variations, and inclusion of a high-latitude heat source representing Joule dissipation of electric current systems. It is concluded that the Joule heating is essential for bringing theoretical predictions into agreement with observations but that the global mean of the required heating during geomagnetically quiet periods is necessarily small compared to global mean solar heating at the same levels.