Physical drivers of marine heat waves intensification in the presence of atmospheric heat waves in the Mediterranean

Atmospheric and marine heatwaves (AHW and MHW, hereafter) are extreme temperature events occurring in an extensive area and sustained in time. In the Mediterranean region, these events have become more frequent in the last decades. Tracking the spatiotemporal evolution of such events is key for the implementation of adaptation measures to cope with their associated impacts both on the population and the environment. The growing frequency of both types of events leads to a higher concurrence of those events, understood as their spatiotemporal co-occurrence. Despite the growing interest in the scientific community about the co-occurrence of AHW and MHW, the details of the physical interaction between such extreme events are not fully described. Several studies pointed out that in the record-breaking European heatwave of 2003, the simultaneous occurrence of AHW and MHW contributed on the exacerbation of the individual events. 

Our hypothesis is that under extreme temperature conditions heat fluxes can change and that probably these changes have an impact in the AHW and/or MHW characteristics. The aim of this work is to investigate the physical mechanisms behind these changes with a special focus on concurrent AHW and MHW events (CHW). Our results show that there is a heat flux intensification during CHW influencing the temperature anomalies. For this study we investigate the AHW, MHW and their concurrence in the Mediterranean basin during the extended summers (May to September) from 1940 to 2022 using ERA5 reanalysis data to characterize the heat fluxes, surface wind and sea level pressure fields, cloud cover, sea surface and 2-meter air temperatures.