Exploring the Impacts of Ocean-Atmosphere Flux Enhancements Due to Convective Wind Gusts in the Community Earth System Model (CESM)

Coupled air-sea interactions play a critical role in moistening the atmospheric boundary layer, subsequently altering convection, clouds, and rainfall on a range time and spatial scales. In the Community Earth System Model version 2 (CESM2), the calculation of ocean surface fluxes currently relies on a Monin-Obhukov formulation using only the grid-mean 10 m wind speed (U10). Deep convection, however, drives subgrid-scale downdrafts that generate large, near-surface wind gusts in observations that are unaccounted for in coarser averages from O(100) km grid boxes. This is particularly problematic in the tropics, where deep convection is most frequent and mean U10 is weak relative to other regions, and yet surface fluxes can be a significant component of the surface energy budget.

In this study, we examine the impact of including a parameterization of subgrid convective gustiness over ocean surfaces in recent development versions of CESM. By enhancing near-surface winds, latent heat fluxes are also increased, leading to a reduction in mean flux biases over many areas of the tropics. Initial analysis suggests that the addition not only impacts the local atmosphere, but can also contribute to reducing biases in the El Nino Southern Oscillation (ENSO). In this talk, we will explore the mean atmospheric responses to gustiness as well as the mechanisms behind an improved ENSO representation in CESM.