Examining the sensitivity of ocean response to oceanic grid resolution in COAMPS-TC during Hurricane Irma

Air-sea interaction during tropical cyclone (TC) passage is still an active research topic which is being investigated by both observational and modeling studies. Recent progress from observational studies to understand basic air-sea processes has led to sub-grid parameterizations within TC forecasting models that are coupled with a 3D ocean model. However, there is still much uncertainty as to what ocean grid scales need to be resolved in coupled TC models to accurately predict air-sea interaction, intensity change, and represent ocean response in a TC. Using the Navy’s Coupled Ocean-Atmospheric Mesoscale Prediction System for Tropical Cyclones (COAMPS-TC), we investigate the sensitivity of ocean processes, air-sea response, and TC intensity to varying ocean horizontal and vertical resolutions for Hurricane Irma, when the TC reaches Category 5 status over the Amazon-Orinoco River plume. The goal of this study aims to investigate the impact of ocean grid resolution on the representation of the ocean mixed layer (OML) heat and salt budget in a complex mesoscale ocean environment. Results indicate that changes in ocean resolution do not affect TC track but have a noticeable influence on TC intensity. As horizontal ocean resolution increases, more mesoscale ocean features are able to be resolved, and thus, interact with the wind stress curl imparted by the TC. OML budget analyses reveal that at coarser horizontal resolutions (> 7.5km), the overall OML response is sensitive to vertical ocean resolution. These resolution sensitives differ based on TC quadrant. Moreover, the dominant OML processes change as horizontal resolution increases. Given that the OML response is indicative of sea surface temperature, air-sea response, and TC intensity, it is vital to understand ocean grid resolution sensitives and how they impact coupled TC forecasts.