In the past 40 years, marine heatwaves (MHWs) have experienced a worldwide increase in duration, intensity, frequency and spatial extent. This trend has been particularly evident in the Mediterranean, where exceptional events were observed during the summers of 2022, 2018 and 2003. This study proposes a twofold analysis of MHWs in the Mediterranean, focusing on their statistical characteristics and physical causes. A satellite dataset is utilized to analyze MHWs via an index, called activity, which aggregates the occurrence, duration, intensity and spatial extent of events. Our results show that the trend toward more active summers for MHWs is strongest in the western Mediterranean basin and long-term warming is the main driver in the whole Mediterranean basin. We also show that in the western and Adriatic Mediterranean region, the increase of SST variability contributes about a third to the MHW activity long-term trend whereas in the central, eastern and Aegean basins, the variability of SST mostly acts to diminish this trend. Through principal component analysis (PCA) of MHW activity, we found that the three most severe summer MHW events in the Mediterranean occur at the same location where the overall trend is highest. Interannual variability increased MHW activity in 2022 around the Balearic Sea, in 2018 in the eastern basins and in 2003 in the central basins. A joint PCA revealed that the long-term trend in MHW activity co-varies with a positive geopotential height anomaly over the Mediterranean, which is consistent with the generation of atmospheric-driven MHWs and which, at the North Atlantic scale, resembles the positive phase of the summer East Atlantic. The additional interannual variability contribution to these three severe summers was associated with western warming and projected onto the positive phase of the summer North Atlantic Oscillation. The increase in MHW over the last 40 years is also associated in the western, central and Adriatic regions with increased downward short-wave radiation and in the eastern Mediterranean with decreased upward long-wave radiation. Increased upward latent heat flux partly compensated for the MHW long-term increase over the whole Mediterranean basin. The interannual variability of MHW activity is related in the western, central and Adriatic basins to increased downward sensible and decreased upward latent heat flux possibly due to warm and humid air intrusion.

在过去 40 年中，海洋热浪 (MHW) 在全球范围内经历了持续时间、强度、频率和空间范围的增加。这一趋势在地中海地区尤为明显，该地区在 2022 年、2018 年和 2003 年夏季观察到了异常事件。这项研究建议对地中海地区的 MHW 进行双重分析，重点关注其统计特征和物理原因。卫星数据集用于通过称为活动的指数来分析 MHW，该指数汇总了事件的发生、持续时间、强度和空间范围。我们的研究结果表明，西地中海盆地的MHW夏季更加活跃的趋势最为强烈，而长期变暖是整个地中海盆地的主要驱动力。我们还表明，在西部和亚得里亚海地中海地区，海温变化的增加对MHW活动的长期趋势贡献了约三分之一，而在中部、东部和爱琴海盆地，海温的变化主要起到减弱这一趋势的作用。通过MHW活动的主成分分析（PCA），我们发现地中海地区三个最严重的夏季MHW事件发生在总体趋势最高的同一地点。年际变化增加了 2022 年巴利阿里海周围、2018 年东部盆地和 2003 年中部盆地的 MHW 活动。联合 PCA 显示，MHW 活动的长期趋势与地中海上空的正位势高度异常共同变化，这与大气驱动的 MHW 的产生一致，并且在北大西洋尺度上类似于正位相夏季东大西洋。对这三个严酷夏季的额外年际变化贡献与西部变暖有关，并预计到夏季北大西洋涛动的正相位。过去 40 年 MHW 的增加还与西部、中部和亚得里亚海地区向下的短波辐射增加以及地中海东部向上的长波辐射减少有关。向上潜热通量的增加部分补偿了整个地中海盆地的MHW长期增加。西部、中部和亚得里亚海盆地的MHW活动的年际变化与下降的感热通量的增加和上升的潜热通量的减少有关，这可能是由于暖湿空气的入侵造成的。