1. A Zonal See‐Saw Variation of Tropical Cyclogenesis Over the Arabian Sea and Bay of Bengal‐South China Sea.
- Author
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Cao, Xi, Wu, Renguang, Wang, Zhibiao, Lan, Xiaoqing, Sun, Ying, Zhao, Junhu, and Du, Zhencai
- Subjects
TROPICAL cyclones ,CYCLOGENESIS ,VERTICAL wind shear ,OCEAN temperature ,VERTICAL motion ,WATER vapor - Abstract
The variation of tropical cyclone (TC) genesis over the North Indian Ocean (NIO) and South China Sea (SCS) during the post‐monsoon season is explored during 1979–2020. A zonal see‐saw variation of TC genesis is detected between the Arabian Sea (AS) and Bay of Bengal (BOB) –SCS (BOBSCS for brevity). More (less) TCs over the AS tend to concur with fewer (more) TCs over the BOBSCS. Analyses of both the observations and the Coupled Model Intercomparison Project Phase 6 outputs show that tripole sea surface temperature (SST) anomalies in the tropical Indian and Pacific Oceans play a crucial role in the zonal see‐saw variation of TC genesis. Positive western Indian (WI) Ocean and tropical central and eastern Pacific (CEP) Ocean SST anomalies and negative western Pacific (WP) SST anomalies induce anomalous ascending and descending motions and high and low humidity transportation to the middle troposphere over the AS and BOBSCS, respectively. Meantime, anticyclonic vorticity anomalies appear in the BOBSCS region and negative anomalies of vertical wind shear are induced over the NIO and SCS. The combined positive contributions of upward motion, mid‐level humidity increase, and low vertical wind shear favor higher TC genesis over the AS, whereas the joint negative effects of downward motion, mid‐level water vapor decrease, and lower‐level anticyclonic vorticity anomalies result in less TC genesis over the BOBSCS. Numerical experiments show a critical role of the WI SST anomalies in the dipole pattern of vertical motion, which is crucial for the zonal dipole variation of TC genesis. Plain Language Summary: Although the tropical cyclones (TCs) frequency number that form over the South China Sea (SCS), Bay of Bengal (BOB) and Arabian Sea (AS) are relatively small, these regions are densely populated, which means that the impacts of TCs can be significant and widespread. The study presents observational and modeling evidence for a see‐saw variation of tropical cyclogenesis between the AS and BOB‐SCS during the post‐monsoon season (September–December). Composite analyses display that the zonal see‐saw connection of tropical cyclogenesis frequency over the AS and BOB‐SCS is closely linked to the zonal tripole distribution of the sea surface temperature anomalies over the tropics of the Indian and Pacific Oceans, which exert a significant influence on the vertical–zonal overturning circulation and the environmental parameters for TC formation over the AS and BOB‐SCS. We conduct an evaluation of 19 CMIP6/AMIP (CMIP6/CMIP) simulations and reveal that 53% (26%) models are able to successfully simulate the zonal dipole pattern of TC‐related variables between AS and BOB‐SCS regions. The present findings may have the potential to enhance the seasonal prediction for tropical cyclogenesis over the SCS, AS and BOB regions. Key Points: A zonal see‐saw variation of TC genesis is detected between the Arabian Sea (AS) and the Bay of Bengal‐South China Sea (BOBSCS)The tripole SST anomalies over the tropical Indian and Pacific Oceans play a crucial role in the zonal see‐saw variation of TC genesisNumerical experiments show a critical role of SST anomalies in the western Indian Ocean in the dipole pattern of vertical motion [ABSTRACT FROM AUTHOR]
- Published
- 2023
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