The GISS global climate-middle atmosphere model. Part I: model structure and climatology

Abstract

The GISS global climate model has been extended to include the middle atmosphere up to an altitude of approximately 85 km. The model has the full array of processes used for climate research, ie numerical solutions of the primitive equations, calculation of radiative and surface fluxes, a complete hydrologic cycle with convective and cloud cover parameterizations etc. In addition, a parameterized gravity wave drag formulation has been incorporated, in which gravity-wave momentum fluxes due to flow over topography, wind shear and convection are calculated at each grid box, using theoretical relationships between the grid-scale variables and expected source strengths. The model produces generally realistic fields of temperature and wind throughout the atmosphere up to approximately 75 km. Important aspects of the current simulation include a proper break between the tropospheric and stratospheric jets, realistic closing off of the wintertime jet in the mesosphere, the observed warm winter/cold summer mesosphere, and a semiannual wind oscillation near the stratopause. The most obvious deficiences are that the long-wave energy itself is somewhat too small in the low and midstratosphere, temperatures are too cold near the model top and are too warm in the polar Southern Hemisphere lower stratosphere during winter. Also, the model generates an inertial oscillation near the equatorial stratopause which may be excessive. -from Authors