GEOGRAPHY

The study reveals the spatiotemporal variation characteristics and physical mechanism of marine heatwaves in the South China Sea


Recently, Wang Chun, a researcher at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, explored the spatiotemporal variation characteristics and physical mechanisms of summer marine heatwaves (MHWs) in the South China Sea under the scenario of increasing subtropical high events in the future strong northwest Pacific Ocean. The related research paper was published in Geophysical Research Letters.

Schematic diagram of SST–cloud negative feedback mechanism. Photo courtesy of the research team

Marine heatwaves are extreme heat events that occur in the ocean, posing serious threats to marine ecosystems, such as coral bleaching and loss of seagrass beds and algal forests. Studies based on different models and scenarios of the Northwest Pacific Subtropical High show that there is a clear increase trend in the future strong Northwest Pacific subtropical high event. So, how will future marine heatwaves in the South China Sea respond to the increase in strong subtropical high events in the northwest Pacific?

Using satellite observations of SST data, reanalysis data and CMIP6 model data, the researchers estimated the spatiotemporal variation characteristics of future summer marine heatwaves in the South China Sea. Studies have shown that future increases in strong Northwest Pacific subtropical high events mainly affect the total number of days of summer marine heatwaves in the South China Sea. Compared with the historical period (1982~2020), the area of the high-value area (> 50 days) of the total number of summer marine heatwave days in the South China Sea in the future will increase significantly. By the end of the century, the total number of summer marine heatwave days in the South China Sea could reach about 34 days/summer. At the same time, the average duration of summer marine heatwaves in the South China Sea has increased significantly, with a single marine heatwave event lasting the longest summer in the second half of the century.

When the subtropical high in the northwest Pacific intensifies in the future, the abnormal easterly wind caused by the anticyclonic circulation will weaken the summer southwest monsoon in the South China Sea, which will reduce the surface wind stress and wind stress curl in the South China Sea, and inhibit the upwelling in the central and southern parts of the South China Sea. Without the cooling effect of upwelling, the surface temperature in the South China Sea will heat up rapidly, leading to an increase in summer marine heatwave events in the South China Sea. When there is a continuous marine heat wave event in the South China Sea, high temperature seawater will enhance surface evaporation and increase latent heat loss. At the same time, convection is strengthened, which leads to the formation of a large number of convective clouds, which in turn reduces solar radiation. This SST–cloud negative feedback mechanism limits the average intensity of summer marine heatwaves in the South China Sea to a lower range, so the average intensity of future summer marine heatwaves in the South China Sea has a weaker response to the strengthening of the Northwest Pacific subtropical high. (Source: China Science News, Zhu Hanbin, Fu Tian)

Related paper information:https://doi.org/10.1029/2023GL103667



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