| Summary: | Previous studies proved that the East Asia summer monsoon circulation, such as monsoon trough (MT) and western Pacific subtropical high (WPSH) are closely correlated with tropical cyclone (TC) activity. Here, we emphasized that the excessive Chukchi-Beaufort (C-B) and Greenland (GL) sea ice sustains from August to the following early autumn and triggers the southeastward propagation of the Rossby wave trains originating from the Arctic across Western Eurasia (Okhotsk Sea) to the western North Pacific (WNP). The resultant abnormal low pressure over WNP, implying a decreased WPSH, provides suitable environmental conditions for TC formation—the enhancement of the lower-level relative vorticity and water moisture, and the decrease of vertical wind shear. For the reduced sea ice, an opposite situation tends to emerge. The persistent combined sea ice signal makes it a physically meaningful precursor for TCF prediction. The cross-validated hindcast and independent forecast based on both the tropical SST and the Arctic sea ice precursors present that the TCF index is predicted with much higher correlation coefficients than the empirical models with only the tropical SST predictors. The results demonstrate that the Arctic sea ice indeed promotes the seasonal prediction capability of the WNP TCF.
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