Upper-Ocean Temperature Variability in the Gulf of Mexico with Implications for Hurricane Intensity
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AbstractStrong winds in tropical cyclones (TCs) mix the ocean, causing cooler water from below the thermocline to be drawn upward, reducing sea surface temperature (SST). This decreases the airsea temperature difference, limits available heat energy, and impacts TC intensity. Part of TC forecast accuracy therefore depends upon the ability to predict sea surface cooling; however, it is not well understood how underlying ocean conditions contribute to this cooling. Here, ~4400 Argo profiles in the Gulf of Mexico were used in a principal component analysis to identify the modes of variability in upper-ocean temperature, and a 1D mixed layer model was used to determine how the modes respond to surface forcing. It was found that the first two modes explain 75% of the variance in the data, with high mode-1 scores being broadly characterized as having warm SST and deep mixed layer and mode-2 scores being characterized as having high SST and a shallow mixed layer. Both modes have distinct seasonal and spatial variability. When subjected to the same model forcing, mode-1- and mode-2-characteristic waters with equal tropical cyclone heat potential (TCHP) respond very differently. Mode-2 SST cools faster than mode 1, with the difference being most pronounced at lower wind speeds and when comparing early-season storms with late-season storms. The results show that using TCHP as a marker for SST response during TC forcing is insufficient because it does not fully capture subsurface ocean thermal structure. This result underscores the need for continual subsurface monitoring so as to accurately initialize the upper ocean in coupled TC models.
