Effects of the 2003 European heatwave on the Central Mediterranean Sea surface layer: a numerical simulation

Abstract

Abstract. The effects of anomalous weather conditions on the sea surface layer over the Central Mediterranean were studied with an eddy resolving regional ocean model by performing a 5-year long simulation from 2000 to 2004. The focus was on surface heat fluxes, temperature and dynamics. The analysis of the time series of the selected variables permitted us to identify and quantify the anomalies of the analysed parameters. In order to separate the part of variability not related to the annual cycle and to locate the anomalies in the time-frequency domain, we performed a wavelet analysis of anomalies time series. We found the strongest anomalous event was the overheating affecting the sea surface in the summer of 2003. This anomaly was strictly related to a strong increase of air temperature, a decrease of both wind stress and upward heat fluxes in all their components. The simulated monthly averages of the sea surface temperature were in a good agreement with the remotely-sensed data, although the ocean regional model tended to underestimate the extreme events. We also found, on the basis of the long-wave period of the observed anomaly, this event was not limited to the few summer months, but it was probably part of a longer signal, which also includes negative perturbations of the involved variables. The atmospheric parameters responsible for the overheating of the sea surface also influenced the regional surface and sub-surface dynamics, especially in the Atlantic Ionian Stream and the African Modified Atlantic Water current, in which flows seem to be deeply modified in that period.