Recently, Dr. Wang Chun, a researcher at the State Key Laboratory of Tropical Ocean Environment/Global Ocean and Climate Research Center of the South China Sea Institute of Oceanology, Chinese Academy of Sciences, collaborated with Associate Professor Fan Hanjie from Sun Yat-sen University to reveal the physical mechanism behind the extreme marine heatwave in the northwest Pacific in July 2022 triggered by monsoon rainfall in India. The findings were published in npj Climate and Atmospheric Science.
Schematic diagram illustrating the mechanism of the extreme ocean heatwave in the northwest Pacific Ocean in July 2022. Image provided by the research team.
"The study investigated the occurrence and development mechanism of this extreme ocean heatwave using satellite observation data, reanalysis data, and climate numerical models," said Song Qianghua, the first author of the paper and a doctoral student at the State Key Laboratory of Tropical Ocean Environment, South China Sea Institute of Oceanology, Chinese Academy of Sciences. In July 2022, an extreme ocean heatwave event occurred in the high-latitude waters of the northwest Pacific Ocean, with the regional average sea surface temperature anomaly reaching up to 5°C, and in some areas exceeding 8°C, making it the strongest ocean heatwave event ever recorded in this region.
The study found that the main cause of this extreme ocean heatwave was atmospheric forcing, specifically the formation of a strong atmospheric blocking high-pressure system over the ocean heatwave area. Under the influence of the high-pressure system, atmospheric convection weakened and cloud cover decreased, leading to increased shortwave radiation from the sun. This process rapidly raised the sea surface temperature, triggering the unprecedented ocean heatwave event in the region. Furthermore, the research showed through climate diagnostic methods and numerical models that the immense latent heat released by extreme precipitation from the Indian summer monsoon generated atmospheric disturbances, which, through the propagation of quasi-stationary Rossby waves, produced and enhanced this strong blocking high-pressure system. The study also found a significant increase in the correlation between Indian summer monsoon precipitation and northwest Pacific Ocean temperatures after 2011 (R=0.97, p<0.01), further demonstrating that the strengthening of Indian summer monsoon rainfall was the main trigger for the extreme ocean heatwave in the northwest Pacific in July 2022.
The study reveals the physical connection between Indian summer monsoon precipitation and ocean heatwaves in the northwest Pacific Ocean, highlighting the impact of interoceanic interactions on ocean heatwaves in the high-latitude waters of the northwest Pacific. The research results provide a theoretical basis for the prediction of future ocean heatwaves in the northwest Pacific Ocean.
The aforementioned research was jointly funded by the National Natural Science Foundation Major Project, the National Key Research and Development Program Project, the National Natural Science Foundation Youth Project, and others.
Link to the related paper: https://doi.org/10.1038/s41612-024-00645-x
