Ocean-atmosphere heat exchange seasonal cycle on the West Florida Shelf derived from long term moored data

Abstract

Twenty-three years of surface meteorological and oceanographic data sampled from moored buoys are used to study the seasonal and interannual variations of ocean–atmosphere heat exchange and its influence on West Florida Continental Shelf (WFS) water temperature and stratification. The data are from the University of South Florida's Coastal Ocean Monitoring and Prediction System (COMPS), part of the Southeast Coastal Ocean Observing Regional Association (SECOORA). Observed are incoming short and longwave radiation, air and sea surface temperatures (AT and SST), barometric pressure, relative humidity, wind velocity, water column velocity profiles, and water column temperature at discrete depths. These data are used to estimate net shortwave and longwave radiation and sensible and latent heat fluxes via the COARE 3.6 algorithm. When combined, these radiative and turbulent heat flux influences are compared with the heating and cooling of the WFS water column and SST. On seasonal average, heating starts in February and lasts through August, with a maximum rate of change in May, while cooling starts in September and lasts through January, with the maximum rate of change in October. Also on seasonal average, SST varies from 18.4 °C in February to 30.4 °C in August at mooring C10 (at the 25 m isobath) and from 20.1 °C in February to 30.2 °C in August at mooring C12 (at the 50 m isobath), the differences in the seasonal range being due to increased ocean circulation influence in deeper water. Both the spring and fall transition onsets, February and August, respectively, occur when the sign of the net heat flux changes. The water column begins to stratify in March, peaking in June–July and lagging the surface heating by one or two months, then decreasing through September at C10 and October at C12. Stratification is also modified by persistent upwelling when the Gulf of Mexico Loop Current (LC) interacts with the WFS slope at its southwest corner near the Dry Tortugas. Interannual temperature anomalies from the seasonal cycle are also related to how the LC interacts with the WFS slope.