Effects of Ocean Heat Transport in Tropical Radiative Convective Equilibrium

A global climate model is run in radiative-convective equilibrium including a slab ocean with a specified ocean heat transport analogous to what is seen in the tropical Pacific. The insolation is varied to create a range of global mean equilibrium temperatures. These results are compared with experiments that do not include a specified ocean heat transport. The ocean heat transport cools the coldest Sea Surface Temperatures (SSTs) and increases the SST contrast. The warmest SSTs change much less with the addition of ocean heat transport because increased atmospheric transport moves energy away from the warm region. The ocean heat transport also increases the efficiency of cooling by outgoing longwave radiation in the subsiding region, allowing for a cooler global mean SST. At colder global mean temperatures ocean heat transport creates a high-contrast state in which abundant low clouds play a strong role in maintaining the SST contrast. This high-contrast state abruptly transitions to a warmer, low-SST-contrast state as the climate is warmed by increasing insolation. At warmer temperatures comparable to the current tropics, the low cloud response is less important than longwave emission in maintaining the SST contrast. Although ocean heat transport cools the climate, it does not much affect the sensitivity of the model climate to increasing insolation. Comparison of the model results to ERA5 reanalysis data shows that mechanisms responsible for the SST distribution and energy budget changes in this idealized model are analogous to variability that occurs over the tropical Pacific Ocean.