Slowdown of the Walker Circulation driven by tropical Indo-Pacific warming.
– Slowdown of Walker Circulation is a robust change, observed over the last century
– Useful testbed for model evaluation
– AGCMs only simulate the reduction of the walker circulation if the correct spatial pattern of SST warming is prescribed. The simulations fail if an “average” warming is applied equally everywhere, for example.
– Weakening of the zonal gradient of SST across the Indo-Pacific region over the last 60 years is largely responsible for the slowdown seen.
– Effect of future SST pattern change uncertainty may extend remotely to densely populated regions.
– Reanalyses affected by errors in the SST warming pattern.
Possible issue – confusion between the Walker circulation, driven by ocean temperatures, with the overturning circulation driven by atmospheric radiative cooling.
Important: Reexamination of the tropical SST data indicates that the true SST trends have been quite different from that in the standard datasets. This difference in warming pattern changes the sign of the mean SLP trend over much of Australia and the Maritime continent.
This may be important in the role of oceans in driving the changes in climate over Australia, and may explain why so many models driven by “observed” SSTs do worse at predicting Australian rainfall trends than those that do not include the observations.