Adverse Impact of Explicit Ocean‐Wave Coupling on the Climatology of Tropical Cyclones and Their Environment in E3SM

Abstract

Upper‐ocean processes play a pivotal role in the development of tropical cyclones (TCs) through their modulation of sea surface temperatures, and consequently, air‐sea fluxes and the large‐scale storm environment. While most fully‐coupled Earth system models represent key processes such as vertical mixing, few incorporate the effect of surface ocean waves. Here, using a regionally refined configuration of the Energy Exascale Earth System Model that can explicitly resolve TCs over the North Atlantic, we conduct simulations to understand how the inclusion of waves may modulate storms in the model by running a configuration where the ocean component is coupled to WAVEWATCH III. Compared to the simulation without waves, TCs are weaker and their activity is reduced in the simulation with waves, especially over the TC main development region. Analysis indicates that a relatively larger positive vertical wind shear bias, which results from a larger cold SST bias and hence, a stronger North Atlantic subtropical high, is likely responsible. Further, an examination of TC cold wakes revealed that the magnitude of storm‐induced SST cooling is reduced in the simulation with waves relative to the simulation without waves, despite evidence of stronger TC‐induced upper‐ocean mixing in the former. This can be attributed to the “background state” effect of waves, which is to produce climatologically deeper mixed layers, being stronger than their “event scale” effect, whereby they enhance mixing during storms. These results suggest that the impact of including waves on TCs in a model may depend on its representation of the mean state.