Tropical expansion and its impact on climate extremes

Recent observational analyses show the tropics have widened over the last several decades. Estimates range from 2-50 latitude since 1979 based on several metrics including a poleward shift of the Hadley cell. Studies have also showed a poleward shift in the tropospheric jets and the storm tracks. Our study investigates the impacts of tropical expansion on hydrological extremes, using observations and model data from the Coupled Model Inter-comparison Project phase 5 CMIP5 data. The effects of tropical expansion on temperature extremes via surface moisture deficits and drought is also investigated. Standardized Precipitation Index (SPI) is used as a proxy for surface moisture deficits. Palmer Drought Severity Index (PDSI) is also used to quantify drought severity and excessive rain estimates. The frequency of drier conditions in regions such as the Southwestern US, and Mediterranean is also studied. Furthermore, the CMIP5 RCP experiments are used to investigate the role of expanding subtropical dry zones on temperature/precipitation extremes through the 21st century. The role of natural variability associated with multi-decadal modes of SST variability in modulating 21st century trends in greenhouse gas (GHG) induced tropical expansion and the corresponding impacts on extremes is also examined.