A THERMOSPHERE-IONOSPHERE-MESOSPHERE-ELECTRODYNAMICS GENERAL-CIRCULATION MODEL (TIME-GCM) - EQUINOX SOLAR-CYCLE MINIMUM SIMULATIONS (30-500KM)

A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure betwe en 30-500 km for equinox, solar cycle minimum, geomagnetic quiet condi tions. The model incorporates all of the features of the NCAR thermosp here-ionosphere-electrodynamics general circulation model (TIE-GCM) bu t the lower boundary has been extended downward from 97 to 30 km (10 m b) and it includes the physical and chemical processes appropriate for the mesosphere and upper stratosphere. The first simulation used Rayl eigh friction to represent gravity wave drag in the middle atmosphere and although it was able to dose the mesospheric jets it severely damp ed the diurnal tide. Reduced Rayleigh friction allowed the tide to pen etrate to thermospheric heights but did not dose the jets. A gravity w ave parameterization developed by Fritts and Lu (1993) allows both fea tures to exist simultaneously with the structure of tides and mean flo w dependent upon the strength of the gravity wave source, The model ca lculates a changing dynamic structure with the mean flow and diurnal t ide dominant in the mesosphere, the in-situ generated semi-diurnal tid e dominating the lower thermosphere and an in-situ generated diurnal t ide in the upper thermosphere. The results also show considerable inte raction between dynamics and composition, especially atomic oxygen bet ween 85 and 120 km.