SIMULATION OF THE ZONAL MEAN CLIMATOLOGY OF THE MIDDLE ATMOSPHERE WITH A 3-DIMENSIONAL SPECTRAL MODEL FOR SOLSTICE AND EQUINOX CONDITIONS

The zonal mean state of the middle atmosphere is simulated by a three-dimensional spectral model, extending approximately 15 up to 120 km, for solstice and equinox conditions. The model includes realistic parameterizations of atmospheric infrared cooling, and a gravity wave formulation based on a combination of LINDZEN's [(1981), J. geophys. Res. 86, 9707] and MATSUNO's [(1982), J. met. Soc. Japan 60, 215] approaches. The temperature distributions for both seasons and the zonal wind distribution for solstice are in satisfactory agreement with the recent empirical model of FLEMING et al. [(1988), NASA Technical Memorandum No. 100697 (85 pp.)]. Net vertical fluxes of horizontal momentum agree well with available systematic observations of gravity waves in the middle atmosphere. Dissipating and breaking waves yield heating rates comparable with net radiation heating in the upper mesosphere and lower thermosphere. Low values of the vertical eddy diffusion coefficient of order 30-50 m2 s-1 are necessary to produce realistic temperatures around the mesopause.