Seasonal and Interannual Variability of Tropical Diurnal Warming of Sea Surface Temperatures

A method for determining the diurnal sea surface temperature (SST) cycle through satellite data has previously been developed by Clayson and Curry (1996). In their work they applied a parameterized equation from Webster et al. (1996) that uses the magnitude of peak solar insolation, the cumulative amount of daily precipitation, and average daily wind speed to compute the diurnal warming of SSTs. This parameterization has been applied to data obtained by the International Satellite Cloud Climatology Project (ISCCP) and Special Sensor Microwave/Imager (SSM/I) data to produce a daily diurnal warming database for the global tropics during the years 1996-2000. Precipitation values were not yet available and were found to play a smaller role in diurnal warming, so they were not used in this study. Daily files of diurnal warming (dSST) were created at a spatial resolution of 0.25 deg. longitude x 0.25 deg. latitude. This study examines the spatial and temporal variability of dSST over the global tropics by examining averages of these values seasonally and year to year and by conducting an EOF analysis of the data for the tropical Atlantic, Indian, and Pacific Oceans. Results show that different atmospheric processes influence dSST for each tropical ocean basin. Also, dSST is shown to be driven by surface fluxes and not the underlying ocean characteristics. However, diurnal warming can affect the depth of mixing and entrainment cooling in the upper ocean by influencing the oceanic stability at the surface.