Effects of the 2003 European heatwave on the Central Mediterranean Sea: surface fluxes and the dynamical response

[摘要] The effects of the 2003 European heatwave on the sea surface layer ofthe Central Mediterranean were studied using a regional 3-D ocean model.The model was used to simulate the period 2000 to 2004 and its performancewas validated using remotely-sensed and in situ data.Analysis of theresults focused on changes in the Sea Surface Temperature (SST) and onchanges to the surface and sub-surface current field.Thispermitted us to identify and quantify the anomalies of atmospheric andsea surface parameters that accompanied the heatwave.The dominant annualcycle in each variable was first removed and a wavelet analysis thenused to locate anomalies in the time-frequency domain.

We found that the excess heating affecting the sea surface inthe summer of 2003 was related to a significant increase in airtemperature, a decrease in wind stress and reduction of allcomponents of the upward heat flux.The monthly averages of the modelSST were found to be in good agreement withremotely-sensed data during the period studied, although the ocean modeltended to underestimate extreme events.The spatial distribution of SSTanomalies as well as their time-frequency location was similar for boththe remotely-sensed and model temperatures. We also found, on thebasis of the period of the observed anomaly, that the event wasnot limited to the few summer months of 2003 but was part of alonger phenomenon. Both the model results and experimental data suggestthe anomalous heating mainly affected the top 15 m of ocean and wasassociated with strong surface stratification and low mixing.

The skill of the model to reproduce the sub-surface hydrographic featuresduring the heatwave was checked by comparison with temperature andsalinity measurements.This showed that the model was generally in goodagreement with observations.The model and observations showed that theanomalous warming also modified the currents in the region, mostnoticeably the Atlantic Ionian Stream (AIS) and the Atlantic TunisianCurrent (ATC). The AIS was reduced in intensity and showed lessmeandering, mainly due to the reduced density gradient and low winds,while the ATC was enhanced in strength, the two currents appearingto modulate each other in order to conserve the total transport ofModified Atlantic Water.

[学科分类] 海洋学与技术