SUMMER AND WINTER GLOBAL STATIONARY EDDY PATTERNS DUE TO MOUNTAINS AND DIABATIC HEATING

The primary goal of this thesis is to examine how much of the observed standing waves can be explained from knowing just the surface inhomogeneities (mountains, ocean, land, snow, etc.). To this end, we developed a steady state, high resolution, global model based on the linearized primitive equations on a spherical geometry in pressure coordinates. The stationary wave patterns obtained by this model during December-January-February (DJF) and June-July-August (JJA) conditions are simulated as a forced response to parameterized mountain effects and diabatic heating by prescribing the zonal basic state from observations. Mountain forcing is parameterized as the vertical p-velocity resulting from the 900 mb zonal flow over the surface topography. The atmospheric diabatic heating is parameterized in terms of prescribed surface physio-geographic conditions and radiation convection parameters. The parameterized heating is then distributed in the vertical, according to a predetermined profile. The parameterized heat source has been compared to GCM derived zonal asymmetries in heating. Over much of the extratropical latitudes of both hemispheres, the model response to parameterized heating compares reasonably well with that due to diabatic heating calculated from a GCM. The phase of the models's midlatitude response to the combined effects of topography and heating, is in reasonable agreement with the observed standing wave features in the troposphere during both DJF and JJA. An agreement between the computed and simulated winds in the tropical and subtropical latitudes can be found, only when we force the model with GCM derived heating. The amplitude of the model's response in the Northern Hemisphere during DJF is low as compared to observations, but sensitivity experiments with decreased model dissipation show an increase in amplitude with almost no effect on phase. In contrast, during JJA the amplitudes and phases are close to those observed. Overall, the Northern Hemispheric extratropical standing wave patterns are simulated better than those in the tropical belt and in the Southern Hemisphere. During DFJ both the mountains and heating seem to be equally important for the extratropics of the Northern Hemisphere, whereas during JJA the response due to heating dominates. During DJF the response due to heating is mostly in phase with that of mountains, whereas in JJA they are almost out of phase. The above results suggest that the present model may be used to study the sensitivity of midlatitude standing waves to surface boundary conditions, at time scales varying from a season to glacial-interglacial periods.