Abstract
Comment
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Oral
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IAMAS
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JMP06 - Advancing air-sea flux process understanding across diverse conditions
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Impacts of subsurface ocean variability on tropical cyclone genesis
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1. Lei Zhou*, Shanghai Jiao Tong University
2. Cong Gao, Princeton University
3. I.-I. Lin, National Taiwan University
4. Chunzai Wang, South China Sea Institute of Oceanology
5. Shoude Guan, Ocean University of China
6. Fei-Fei Jin, University of Hawaii
7. Raghu Murtugudde, University of Maryland
*Presenting Author
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The upper ocean provides thermal energy to tropical cyclones (TCs). However, the impact of the subsurface ocean on TC genesis has been largely overlooked. Here, we show that subsurface variability associated with variations in the 26C isothermal depth has pronounced effects on TC genesis over the global ocean. The sea surface wind stress and its curl prior to tropical cyclogenesis are large enough to perturb the ocean interior to more than one hundred meters due to entrainment and upwelling. The 26C isothermal depth can vary by tens of meters to significantly modify the upper ocean heat content. Consequently, sea surface temperature anomalies are induced under nascent TCs and tropical cyclogenesis is modulated. A specific example is the contrast in TC genesis numbers between El Ni?o and La Ni?a over the northwestern Pacific. During El Ni?o, the western Pacific warm pool expands eastward. However, the number of TCs does not increase significantly with the expanding pool; the number of TCs remains comparable between El Ni?o and La Ni?a. The reason is that the change in subsurface heat content counteracts the favorable warm SSTs in the tropical central North Pacific. Due to the anomalous positive wind stress curl, the 26C isotherm is shifted over this region during El Ni?o, and the heat content in the tropical central-north Pacific decreases even though warm SST anomalies prevail. This negative correlation between SST and 26C isotherm depth anomalies is opposite to the positive correlation in the tropical eastern and western Pacific. Overall, our results provide evidence for an unexpected relationship between interior ocean variability and tropical cyclogenesis. The specific dynamics of the influences of ocean subsurface variability on TC call for dedicated further research, which is expected to advance our understanding of TC dynamics and improve TC simulation/forecasting.