Response of the sea surface temperature to heatwaves during the France 2022 meteorological summer

Abstract. Summer 2022 was memorable and record-breaking, ranking as the second hottest summer in France since the beginning of the measurements, with a seasonal average of 22.7 °C. In particular, France experienced multiple record-breaking heat waves. As the main heat sink of the Earth system, the oceans are at the forefront of events of this magnitude, which enhance oceanic disturbances such as marine heat waves. In this study, we investigated French maritime basins sea surface temperature to determine the ability of satellite measurements to track the response of surface waters to these events. Despite some gaps in data availability, we showed that during the meteorological summer of 2022, the mean sea surface temperature was between 1.3 °C and 2.6 °C above the long-term average (1982–2011). A focus on the heat wave from 31 July to 13 August was carried out and showed a significant sea surface temperature response to the heat wave with maximum temperatures measured locally at 30.8 °C in the North-western Mediterranean sea. Beyond the response to intense surface air temperatures, the contribution of other atmospheric variables was not negligible. Thus, we have shown that France experienced an August with above-average surface solar radiation correlated with below-average total cloud cover and anomalies in the distribution and intensity of wind speeds. The response to these different contributions depends on the hydrodynamic conditions, in particular the tides that ensure turbulent mixing. This is why the response is more pronounced in the Mediterranean, where the absence of dynamic mixing (below-average surface wind speed) is associated with an absence of tides. Our results were in line with previous studies and we confirmed here that even if the Mediterranean is a climate change hotspot, all maritime front are affected by a warming of surface waters. Our study therefore demonstrated the need for an efficient and sustainable operational system combining polar orbiting and geostationary satellites to prevent the alterations that threaten the oceans in the context of climate change.