Assessment of the spectral downward irradiance at the surface of the Mediterranean Sea using the OASIM ocean-atmosphere radiative model

Abstract. A multiplatform assessment of the Ocean–Atmosphere Spectral Irradiance Model (OASIM) radiative model focussed on the Mediterranean Sea is presented. BOUée pour l'acquiSition d'une Série Optique à Long termE (BOUSSOLE) mooring and biogeochemical Argo (BGC-Argo) float optical sensor observations are combined with model outputs to analyse the spatial and temporal variabilities in the downward planar irradiance at the ocean-atmosphere interface. The correlations (r) between the data and model are always higher than 0.6. At the scale of the BOUSSOLE sampling (15-minute temporal resolution), the root mean square difference (RMSD) oscillates at approximately 30~40 % of the averaged model output and is reduced to approximately 10 % when the daily variability is filtered out. Both BOUSSOLE and BGC-Argo indicate that the bias is high for the irradiance at 412 nm, whereas it decreases to less than 5 % at the other wavelengths. Analysis of atmospheric input data indicates that the model skill is strongly affected by cloud dynamics and seasonality. High skills are observed during summer when the cloud cover is low.