ESA STSE Project “Sea Surface Temperature Diurnal Variability: Regional Extend – Implications in Atmospheric Modelling”

Abstract

Sea Surface Temperature (SST) and ocean-surface winds have been identified as essential variables by the Global Climate Observing system (GCO). Satellite observations have aided the understanding of air-sea interactions and the important role these two parameters hold in climate related studies, atmospheric and oceanic modelling, bio-chemical processes and oceanic CO2 studies. The diurnal variability of SST, driven by the coincident occurrence of low enough wind and solar heating, is currently not properly understood. Atmospheric, oceanic and climate models are currently not adequately resolving the daily SST variability, resulting in biases of the total heat budget estimates and therefore, demised model accuracies. The ESA STSE funded project SSTDV:R.EX.-IM.A.M. aimed at characterising the regional extend of diurnal SST signals and their impact in atmospheric modelling. This study will briefly present the final project findings regarding the analysis of hourly SEVIRI SSTs from SEVIRI over the Atlantic Ocean and the European Seas, revealing the regional extend of diurnal warming. As satellite SSTs are representative of the upper centimetre of the water column, they do not provide information of the vertical extend of diurnal signals. Drifting buoys provide measurements close to the surface but are not always available. Moored buoys are generally not able to resolve the daily SST signal, which strongly weakens with depth within the upper water column. For such reasons, the General Ocean Turbulence Model (GOTM) was used to resolve the vertical temperature structure of the upper water column and provide the link between surface temperatures and the ones observed at some depth. The model proved able to reproduce signals observed from satellite and in situ instruments, thus can be a candidate model for operational analysis of the daily SST variability. Such an analysis can be useful for the already operational L4 SST analysis products. Moreover, the project aimed at characterizing how the diurnal SST signals impact atmospheric modelling. Hourly SST fields, were used to initialize the high resolution Weather Research & Forecasting (WRF) model. The perturbations in the atmospheric model, associated with the daily SST cycle were assessed through comparisons of the modelled 10-m wind fields against the ESA's ENVISAT ASAR 10-m winds and in situ measurements at various atmospheric levels, from meteorological masts located offshore. The project resulted in expanding the scientific background for understanding the spatial and temporal variability of key climate variables and their representativity in atmospheric and oceanic models.