Effect of Land-Sea Contrasts on the Large-Scale Equatorial Circulation

What is the difference between the circulation created over an equatorial warm pool and that over a continent or an archipelago? The present work addresses this question using cloud-resolving simulations in a longitudinal channel configuration, with latitude-independent surface conditions. The presence of flat continental surfaces appears as efficient as a warm pool in creating a large-scale circulation. Moreover, there is little difference between a flat archipelago and a flat continent of the same longitudinal extent in terms of the overall intensity of the large-scale circulation, but the spatial structure of the circulation differs, with a break-down of the longitudinal symmetry in the presence of a continent. Finally, the addition of mountains on an archipelago appears not to change the overall intensity of the circulation, but it concentrates the circulation over the outer islands. Our results suggest that the land-sea contrasts determine the locations of the ascending branches of the Walker circulation, and that the intensity of these branches is determined by (i) the extent of the archipelago or continent underneath and (ii) the surrounding sea surface temperature.