Sensitivity of modelled Antarctic climate to surface and boundary-layer flux parametrizations

The Hadley Centre climate model version HadAM2 is used to study the sensiti vity of modelled Antarctic climate to the parametrization of surface and bo undary-layer heat fluxes under stable conditions. Specifically, the impact of changing the dependence of surface exchange coefficients and eddy diffus ivities on the Richardson number is investigated. Three alternative paramet rizations are implemented; in all of these the exchange coefficients decrea se more rapidly with increasing stability than they do in the standard para metrization used in the model. When only the surface flux scheme is replace d by one of these alternatives, cooling is largely restricted to the surfac e, with some compensating warming occurring at the lowest atmospheric level s, and little change is seen in the low-level wind field over Antarctica. i f alternative schemes are implemented both at the surface and in the bounda ry layer, widespread cooling occurs at the surface and at the lowest one or two atmospheric levels. The increased negative buoyancy thus generated cau ses significant increases in the speed of katabatic winds blowing down the coastal slopes of Antarctica. Colder and stronger offshore winds lead to in creased cooling of the Antarctic coastal waters. In a coupled model, this c ould impact on the production of sea ice and ocean-bottom water. The modell ed temperature changes appear to show both a direct response to changed bou ndary-layer heat-flux divergence and an indirect response as a result of th e consequent changes to the low-level circulation.