The Influence of the Barrier Layer on SST Response during Tropical Cyclone Wind Forcing Using Idealized Experiments

Abstract

AbstractMultiple studies have shown that reduced sea surface temperature (SST) cooling occurs under tropical cyclones (TCs) where a fresh surface layer and subsurface halocline exist. Reduced SST cooling in these scenarios has been attributed to a barrier layer, an upper-ocean feature in the tropical global oceans in which a halocline resides within the isothermal mixed layer. Because upper-ocean stratification theoretically reduces ocean mixing induced by winds, the barrier layer is thought to reduce SST cooling during TC passage, sustaining heat and moisture fluxes into the storm. This research examines how both the inclusion of salinity and upper-ocean salinity stratification influences SST cooling for a variety of upper-ocean thermal regimes using one-dimensional (1D) ocean mixed layer (OML) models. The Kraus–Turner, Price–Weller–Pinkel, and Pollard–Rhines–Thompson 1D OML schemes are used to examine SST cooling and OML deepening during 30 m s−1 wind forcing (~category 1 TC) for both temperature-only and temperature–salinity stratification cases. Generally, the inclusion of salinity (a barrier layer) reduces SST cooling for all temperature regimes. However, results suggest that SST cooling sensitivities exist depending on thermal regime, salinity stratification, and the 1D OML model used. Upper-ocean thermal and haline characteristics are put into context of SST cooling with the creation of a barrier layer baroclinic wave speed to emphasize the influence of salinity stratification on upper-ocean response under TC wind forcing.