Energy Exchange: The Relationship between Sea Surface Salinity, Enthalpy, and North Atlantic Tropical Cyclone Intensity

Tropical cyclone (TC) intensification strongly depends on energy exchange between the ocean surface and the atmosphere. Sea surface salinity affects evaporation rates and thus latent heat flux over the ocean, as fresh water evaporates more readily than salt water at the same temperature and pressure, but sea surface salinity is highly variable in the tropical North Atlantic Ocean. The Amazon and Orinoco Rivers pump fresh water from South America into the North Atlantic main development region, producing a region of lower salinity and warm sea surface temperatures. In contrast, the region northeast of Hispaniola is marked by warm yet highly saline waters. However, both of these areas often produce rapidly intensifying TCs.

Past work has documented a relationship between the Amazon-Orinoco plume and TC intensity, but an assessment of sea surface salinity’s effects on enthalpy flux within the plume region and the area northeast of Hispaniola has not been performed. To accomplish this goal, we investigate the impact of sea surface salinity on enthalpy flux in these two areas during benign conditions and during TC passage. Over the period 1985-2015, each region is quantified using monthly sea surface salinity values from the CMCC Global Ocean Reanalysis System (C-GLORS). Within each region, 6-h TC intensity changes and translation speeds are compared to daily enthalpy flux and 2-m temperature and humidity values from the Woods Hole Oceanographic Institution’s Objectively Analyzed air-sea Fluxes (OAFlux) dataset. The results will be compared with satellite measures of salinity to assess its potential benefit for TC intensity forecasts.