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 (SSTG) has undergone a significant warming trend at a rate of similar to 0.2 degrees C per decade. The SSTG 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 SSTG are well simulated. Both observation and model simulations demonstrate that the upward tendency in SSTG primarily results from the environmental SST warming over MCS genesis regions rather than the changes in MCS genesis location. A continuous increase in SSTG is projected in a warming simulation, but the relationship between SSTG and upper-tropospheric temperature remains unchanged, suggesting that the tropical tropospheric temperature generally follows a moist-adiabatic adjustment.