Climate variability in the oceans and tropical atmosphere

This dissertation addresses two important climate-related problems. The first problem is the heat budget in the oceans. To address this problem I examine the seasonal heat transport in the North Pacific and North Atlantic Oceans. My results indicate that in midlatitudes surface heat flux from the atmosphere is largely balanced by seasonal storage within the ocean, while equatorward of 15°N, divergence of heat transport balances seasonal storage. The seasonal cycle of heat transport in the Pacific is in phase with the annual migration of solar radiation, transporting heat from the summer hemisphere to the winter hemisphere. Vertical and zonal decompositions of the heat budget highlight the important contributions from the annual cycle of wind-drift within the mixed layer and adiabatically compensating return flow. The annual cycle of heat transport in the North Atlantic is also large. Here too wind-driven transports play a role, although not as strongly as in the Pacific, and this is an important reason for the differences in heat transport between the basins. Our analysis shows the extent to which seasonally varying geostrophic currents and seasonal diabatic effects are relatively more important in the Atlantic.; The second problem I address is on the modeling climate variability in tropical Atlantic atmosphere. To address this problem I examine simulations from six Atmospheric General Circulation Models, together with observational data beginning with their time-mean and seasonal cycles. My analysis identifies excessive surface winds away from the equator and excessive latent heat flux. On the other hand, the seasonal cycle of the winds is well simulated. I then examine year-to-year variability. I find the models are generally successful in reproducing the observed variability of surface winds. However, significant differences exist in the spatial patterns of key variables between simulations and observations and among simulations themselves. All models fail to reproduce the wind-latent heat feedback believed to be essential to interannual variability in this basin. The cause of this failure appears to lie in problems with continental moisture.