ESA STSE Project ''Sea Surface Temperature Diurnal Variability: Regional Extend - Implications in Atmospheric Modelling''
Karagali, Ioanna1; Hasager, Charlotte1; H°yer, Jacob2
1DTU Wind Energy, Technical University of Denmark, DENMARK; 2Danish Meteorological Institute, DENMARK

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. Moreover, diurnal SST variability complicates the merging of SST fields from different satellite sensors and is a source of bias for the satellite wind retrieval algorithms. The ESA STSE funded project SSTDV:R.EX.-IM.A.M. aims at characterizing the regional extend of diurnal SST signals and their impact in atmospheric modelling. The project was initiated on January 2013 and will have a duration of 2 years. The 6-year long SEVIRI (MSG) hourly SST fields will be used to perform a low, mid and high latitude evaluation of the diurnal cycle and identify regional patterns. ENVISAT AATSR SSTs will be used for validation purposes along with drifting and moored buoy measurements. Satellite SSTs are representative of the upper centimeter of the water column but understanding of the vertical extend of diurnal signals is essential. 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. The General Ocean Turbulence Model (GOTM) is able to resolve the vertical temperature structure of the upper water column and will be implemented for comparison with satellite SSTs, moored and drifting buoys in order to interpret potential mismatches. This will finalize the first part of the project during which a characterization of the regional diurnal signals will be performed aiming at a more thorough understanding of the spatial and vertical extend of the daily SST cycle. The second part of the project aims at characterizing how the diurnal SST signals impact atmospheric modelling. Hourly SST fields, when available, will be used to initialize the high resolution Weather Research & Forecasting (WRF) model, currently operational in DTU. The model's performance will be also be assessed when diurnal signals are modeled by a simple parametrization scheme. The perturbations in an atmospheric model, associated with the daily SST cycle will be assessed through comparisons of the modeled 10-m wind fields against the ESA's ENVISAT ASAR 10-m winds (retrieved at DTU) and in situ measurements at various atmospheric levels, from meteorological masts located offshore. Heat flux error estimates will be assessed and compared with the SEVIRI SSI & SLI products. The proposed project aims at expanding the scientific background for understanding the spatial and temporal variability of key climate variables and their representativity in atmospheric and oceanic models. ESA SENTINEL-1 and SENTINEL-3 are highly anticipated as new satellite observations for 10-m winds and SST will be useful for the continuation of this research project. ESA's future ADM-Aeolus mission will provide satellite observations of vertical wind profiles, offering the possibility of investigating the potential signature of diurnal SST signals at higher atmospheric levels and validating the modeled wind fields at various heights.