Sea surface temperature pattern influence on monsoon variability and change

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Climate change will likely increase monsoon rainfall but lead to greater variability and extremes. However, global climate models (GCMs) disagree on the warming pattern of tropical sea surface temperatures (SSTs) as well as regional changes in monsoon rainfall. GCMs also have large biases in monsoon winds and rainfall in the present climate, which increases uncertainty in their climate projections for the future, although they largely capture relative differences in monsoon strength across different continents. To interpret climate model projections, we need a physically based understanding of how monsoons respond to different SST patterns. Previous studies often attributed the relative strength and reliability of the Asian monsoon (compared to African or North/South American monsoons) to differences in continental area, orography, or dynamical forcing from jet or wave interactions. This project will investigate the effects of SST asymmetries such as the Indo-Pacific warm pool on monsoon strength. The hypothesis is that warmer SSTs upwind of certain off-equatorial tropical land regions play a dominant role in increasing the relative strength of a corresponding monsoon because of the moisture and near-surface moist static energy that they supply, which allows for more rainfall and a stronger monsoon circulation.Main questions: 1. How do zonal SST asymmetries affect the relative strength of monsoons in different regions and continents? 2. What implications do different patterns of SST warming in climate projections have for potential regional monsoon changes?3. Can we use observed patterns of 20th-century SST change to inform or constrain future projections of regional monsoons?For this PhD project, the student will undertake research that will lead to improvements in our understanding of how monsoon rainfall interacts with moisture sources and how monsoons might change in the future. The work will involve performing and analysing global climate model experiments, including state-of-the-art of high-resolution process model simulations as well as observations and coarser-resolution simulations. The student will work closely with scientists at the Met Office in Exeter, both remotely and during in-person visits.