Significant Increase in Sea Surface Temperature at the Genesis of Tropical Mesoscale Convective Systems

An event-based assessment of the sea surface temperature (SST) threshold at the genesis of tropical mesoscale convective systems (MCSs) is performed in this study. We show that this threshold (SST_G) has undergone a significant warming trend at a rate of ∼0.2°C per decade. The SST_G shows a remarkable correspondence with the tropical mean SST and upper-tropospheric temperature on interannual and longer timescales. Using a high-resolution global climate model that permits realistic simulations of tropical MCSs, we find that the observed features of SST_G are well simulated. Both observation and model simulations demonstrate that the upward tendency in SST_G primarily results from the environmental SST warming over MCS genesis regions rather than the changes in MCS genesis location. A continuous increase in SST_G is projected in a warming simulation, but the relationship between SST_G and upper-tropospheric temperature remains unchanged, suggesting that the tropical tropospheric temperature generally follows a moist-adiabatic adjustment.