An operational analysis system for the global diurnal cycle of sea surface temperature: implementation and validation

Abstract

An operational system for producing a global diurnally varying analysis of skin sea‐surface temperature (SST) has been developed at the Met Office. Skin SST is formulated as the sum of a foundation temperature, a warm‐layer temperature difference, and a thermal skin temperature difference. Foundation temperature is taken from the Operational Sea surface Temperature and sea Ice Analysis (OSTIA) system, while numerical models are used for the warm layer and thermal skin layer. Both the thermal skin layer and warm‐layer models are forced using outputs from the Met Office's numerical weather prediction system. Data assimilation is used to improve estimates of the warm layer, with observations coming from the geostationary SEVIRI and GOES‐W instruments, as well as the polar orbiting NOAA‐AVHRR sensors. The SST observations of these instruments are converted to observations of the warm‐layer temperature difference by subtracting an instrument‐specific foundation SST calculated using just night‐time data from that sensor. A quality control procedure removes warm‐layer observations where the satellite‐specific foundation estimates are less robust due to lack of data.Validation of the analysis system has been performed by comparing the model to the assimilated satellite data, and to independent near‐surface observations from Argo floats. The mean state of the system was assessed via a comparison to a climatology generated from drifting buoys. Results from the validation show that the system does a good job of replicating the climatology and that assimilation improves the analysis when assessed against Argo. However, the system has been found to underestimate the diurnal range of skin SST by approximately 0.1–0.3 °C on average. Data from the system are available free of charge from the Copernicus Marine Environment Monitoring Service.