A diurnal-cycle resolving sea surface temperature product for the tropical Atlantic

This paper focuses on the problem of generating sea surface temperature (SST) fields that resolve the diurnal cycle for modeling applications, using the tropical Atlantic Ocean as a test site. Our approach was to take advantage of geostationary satellite observations as the diurnal signal source to produce gap-free optimally interpolated (OI) SST fields. The OI schema merges microwave data from the Advanced Microwave Scanning Radiometer (AMSR) and infrared data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) to produce diurnal optimally interpolated SST (DOISST) maps every 3 h on a 25 km grid combining the capability of AMSR to provide nearly bias-free daily SST estimates with the opportunity offered by SEVIRI to monitor the evolution of the SST over the day. Comparison of the SEVIRI data (distributed by the Ocean and Sea Ice Satellite Application Facility (SAF)) with in situ buoy measurements (Pilot Research Moored Array in the Tropical Atlantic) revealed a SAF spatial bias that was greater north of the equator than to the south. This was further confirmed using the Coriolis data set that showed a wide band of SAF high bias values (>0.6 K) which extended diagonally (NW ’ SE) across the tropical Atlantic. In contrast, the AMSR bias pattern was essentially flat (<0.2 K), justifying its use as a reference field to compute the SAF adjustment and to further investigate the spatial-temporal variability of the SAF bias. Analysis of the SAF-AMSR difference revealed strong similarities to ITCZ-related patterns observed in aerosol, columnar water vapor, and wind fields. Due to the bias dependence on atmospheric factors that have pronounced spatial variability and short time scales, the adjustment needs to be performed daily.