High sensitivity of tropical precipitation to local sea-surface temperature

Abstract

Precipitation and atmospheric circulation are the coupled processes through which tropical ocean surface temperatures drive global weather and climate. Influences of local ocean temperatures on precipitation are hard to disentangle from remote effects of conditions elsewhere; and the full influence of the recently-discovered shallow circulations is unclear. Uncertainty in precipitation observations, and limited observations of circulation , further obstruct understanding. Despite decades of research, persistent biases remain in many numerical model simulations, including excessively-wide tropical rainbands, the ‘double-intertropical convergence zone (ITCZ) problem’ and too-weak responses to the El Niño Southern Oscillation (ENSO). These demonstrate stubborn gaps in our understanding, and reduce confidence in forecasts and projections. Here we show that the real world has a high sensitivity of seasonal tropical precipitation to local sea-surface temperatures (higher than in all but 4 of the 47 models studied), associated with strong shallow circulations. Our results apply to both temporal and spatial variation, over regions where climatological precipitation is around 1 mm/day or greater. Novel analysis of multiple independent observations, combined with physical constraints and model data, underpin these findings. A large spread in model behaviour is further linked to differences in shallow convection, providing a focus for accelerated research, to improve seasonal forecasts through multidecadal climate projections.