WARM POOL PHYSICS IN A COUPLED GCM

The physics of the Indo-Pacific warm pool are investigated using a cou pled ocean atmosphere general circulation model. The model, developed at the Max-Planck-Institut fur Meteorologie, Hamburg, does not employ a flux correction and is used with atmospheres at T42 and T21 resoluti on. The simulations are compared with observations, and the model's me an and seasonal heat budgets and physics in the Indo-Pacific warm pool region are explored for the T42 resolution run.Despite the simulation of a split intertropical convergence zone, and of a cold tongue that extends too far to the west, simulated warm pool temperatures are cons istent with observations at T42 resolution, while the nl resolution yi elds a cold bias of 1 K. At T42 resolution the seasonal migration of t he warm pool is reproduced reasonably well, as are the surface heat fl uxes, winds, and clouds. However, simulated precipitation is too small compared to observations, implying that the surface density flux is d ominated by fluxes of heat. In the Pacific portion of the warm pool, t he average net heat gain of the ocean amounts to 30-40 W m(-2). In the northern branch, this heat gain is balanced by vertical advection, wh ile in the southern branch, zonal, meridional, and vertical advection cool the ocean at approximately equal rates. At the equator, the surfa ce heat flux is balanced by zonal and vertical advection and vertical mixing. The Indonesian and Indian Ocean portions of the warm pool rece ive from the atmosphere 30 and 50 W m(-2), respectively, and this flux is balanced by vertical advection. The cooling due to vertical advect ion stems from numerical diffusion associated with the upstream scheme , the coarse vertical resolution of the ocean model, and near-inertial oscillations forced by high-frequency atmospheric variability. The se asonal migration of the warm pool is largely a result of the seasonal variability of the net surface heat flux; horizontal and vertical adve ctions are of secondary importance and increase the seasonal range of surface temperature slightly everywhere in the warm pool, with the exc eption of its southern branch. There, advection reduces the effect of the surface flux. The seasonal variability of the surface heat flux in turn is mainly determined by the shortwave radiation, but evaporation modifies the signal significantly. The annual cycles of reduction of solar radiation due to clouds and SST evolve independently from each o ther in the Pacific portion of the warm pool; that is, clouds have lit tle impact on SST. In the Indian Ocean, however, clouds limit the maxi mum SST attained during the annual cycle. In the western Pacific and I ndonesian portion of the warm pool, penetrative shortwave radiation le ads to convective mixing by heating deeper levels at a greater rate th an the surface, which experiences heat losses due to turbulent and lon gwave heat fluxes. In the deeper levels, there is no mechanism to bala nce the heating due to penetrative radiation, except convection and it s attendant mixing. In the Indian Ocean, however, the resulting vertic al heating profile due to the surface fluxes decreases monotonically w ith depth and does not support convective mixing. Concurrently, the wa rm pool is shallower in the Indian Ocean compared with the western Pac ific, indicating that convective mixing due to penetrative radiation i s important in maintaining the vertical structure of the Pacific porti on of the warm pool.