The Decadal Variation of Eastward-Moving Tropical Cyclones in the South China sea During 1980-2020

摘要

The track of tropical cyclones (TCs) formed in the South China Sea (SCS) can be divided into eastward and westward directions. Significant decadal variation during 1980-2020 only exists in the number of eastward-moving TCs, especially during July-September, with 47% TCs moving eastward during 1994-2004 (Period II), 22% during 1980-1993 (Period I) and only 15% during 2005-2020 (Period III). This decadal change is related to the zonal shift of Western Pacific Subtropical High (WPSH). An eastward-retreated WPSH during 1994-2004 leads to upward motion and westerly flow anomaly over the northern SCS, and therefore favors TC genesis and eastward motion. The eastward-retreated WPSH is associated with a warm sea surface temperature anomaly over the tropical western-central Pacific which induces a cyclonic flow and weakens the WPSH. With the weaker modulation of WPSH, stronger intraseasonal oscillation (ISO) in the SCS during Period II favors eastward-moving TCs due to the westerly flow associated with the ISO. @@@ Plain Language Summary Tropical cyclones (TCs) formed over the South China Sea (SCS) can move either eastward or westward. Eastward-moving TCs can make landfall along the eastern coast of China, the Philippines, and Taiwan Island, or entering western North Pacific. Meanwhile, westward-moving TCs usually make landfall along the coasts of southern China and Vietnam. Our study reveals a significant decadal variation of eastward-moving TCs. More TCs moved eastward during 1994-2004 due to enhanced westerly and convective activity associated with an eastward-retreated Western Pacific Subtropical High, which is caused by the Gill-pattern response to the warm sea surface temperature anomaly over the western-central Pacific. The other reason for a decadal variation of eastward-moving TCs over the SCS is the stronger intraseasonal oscillation activity during 1994-2004, which induces the convective activities and westerly flow anomaly over the main TC genesis region.

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