Mediterranean marine heatwaves: atmospheric drivers and ocean feedback

Abstract

The influence of air–sea heat fluxes on the evolution of marine heatwaves (MHWs) in the Mediterranean was examined over the 1982–2024 summer periods. MHW detection was performed on detrended sea surface temperatures (SSTs), and the application of a minimum spatial coverage threshold of 15% of the Mediterranean Basin provided a catalogue of the most extreme MHW events. Analysis of composite surface flux anomalies shows that latent heat flux (LHF) anomalies dominate the contribution of the air–sea heat flux budget to MHW variability, with negative LHF anomalies before an event and positive LHF anomalies after an event. An alternative MHW detection method which defines MHW events from time series of the principal components (PCs) of MHW intensity was used. This method revealed distinct atmospheric patterns associated with the different phases of an MHW event. Before an MHW event, weakened winds reduce outgoing LHF, trapping heat within the ocean. After an MHW event, a steepening humidity gradient and strengthened winds increase outgoing LHF and heat release into the atmosphere. These results highlight the significant role that LHF plays in the interactions between MHW events and the atmosphere, and the contrasting contributions of wind speed and humidity gradient during MHW onset and decline.

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