The record-breaking 2022 long-lasting marine heatwaves in East China Sea

In 2022, there were record-breaking long-lasting marine heatwaves in the East China Sea, which persisted for 62 days during boreal summer. It was more than sixfold compared to the average duration of the marine heatwaves, which is 9.73 days. It would be recorded as a year when not only marine heatwaves but also various extreme events occurred throughout Asia, such as the summer flood in China and Pakistan. The question arises whether it is caused by La Niña, the first “triple-dip” of the century. Here we will show key local and remote processes that caused the 2022 long-lasting marine heatwaves in the East China Sea. We have conducted a diagnostic analysis based on the mixed-layer heat budget equation to discover the characteristics of the marine heatwaves, i.e., frequency, duration, and intensity. Based on the equation, we found that weakening ocean vertical mixing and entrainment caused by a density stratification would drive the onset of the marine heatwave in the East China Sea. A large river discharge from the Yangtze River related to extreme rainfall in China would be responsible for the stratification by inducing a shallow mixed layer, and it could affect the weak ocean dynamics. Simultaneously, an anomalous anticyclonic circulation was settled in the corresponding region, and the combined effect of the ocean and atmosphere led to the onset of the marine heatwave. The anticyclonic circulation was sustained longer, resulting in the prolonged marine heatwaves in the East China Sea via enhanced shortwave radiation. In this study, we will discuss further where the stationary Rossby wave train originated and how it could lead to the persistent anticyclonic circulation in the East China Sea.