The Influence of SST on Walker Circulation Strength

Climate models struggle to reproduce observed trends in WC strength, and have large spread in future projections of WC strength across models. Concurrently, climate models struggle to reproduce observed trends in tropical SSTs. It is clear that these biases are related: some proposed indices of WC strength are even defined by the zonal SST gradient over the tropical Pacific. On the other hand, AMIP simulations with different models have a large spread in WC strength and its response to warming (as measured using vertical velocity) despite having all the same SSTs. Here we seek to understand the relative influences of SST, including SST gradients, and other processes in setting biases and intermodel spread in WC strength and its trends. We estimate that if GCMs all had the same SSTs, then WC trend estimates would better match those of reanalysis, but substantial spread would remain due to differences in atmospheric model physics.