Variability of Tropical Diurnal Sea Surface Temperature*

Abstract A dataset consisting of daily diurnal warming values from 1996 through 2000 covering the global Tropics (30°N through 30°S) at 0.25° × 0.25° resolution has been created using a parameterization for the diurnal warming developed previously. The inputs to the parameterization are the peak shortwave solar radiation [determined from International Satellite Cloud Climatology Project (ISCCP) data] and daily averaged wind speed [determined from Special Sensor Microwave Imager (SSM/I) data]. Comparisons with Tropical Ocean Global Atmosphere (TOGA) Tropical Atmosphere Ocean (TAO) and Pilot Research Moored Array in the Tropical Atlantic (PIRATA) buoys show that the biases are small (mean bias is 0.0012°C; the standard deviation and correlation are 0.26°C and 0.74) and show no discernable geographic bias. The 5-yr average shows that throughout most regions the values are small, with higher values (approaching 1°C) in the northern Indian Ocean, the western equatorial Pacific, the equatorial eastern Pacific, and several coastal regions. An EOF analysis of the variability indicates that seasonal variability is the most dominant form for each of the basins; in the Atlantic and Pacific basins it is north–south following the solar cycle. In the Indian Ocean the seasonal cycle is dominated by monsoonal variability; both the northern and southern portions of the basin have above-mean or below-mean values at the same times. Seasonal shortwave variability is responsible for the second mode in the Indian Ocean. East–west dipole weight structures appear in the spatial patterns for mode 2 in the Pacific and mode 3 for the Atlantic and Indian Oceans. These modes also display seasonally varying characteristics, with late 1997 and early 1998 being somewhat anomalous in the Pacific and Indian Oceans.