Abstract
This article investigates the relationship between spring (March-May) North Atlantic Oscillation (NAO) and the tropical cyclone genesis frequency (TCGF) over the western North Pacific (WNP) from June to November. It is found that their relationship appears insignificant from 1950 to 1971, intensifies significantly from 1972 to 2010, and then weakens again since 2011. The interdecadal change of this relationship is strongly influenced by the meridional displacement of the North Atlantic jet stream (NAJS). During 1972–2010, the NAJS is located southward, facilitating the spread of Rossby-wave energy to the equatorial region and enhancing the NAO impact on sea surface temperatures (SSTs) over the tropical North Atlantic (TNA). Generally, positive (negative) phases of the NAO relate to negative (positive) TNA SST anomalies in spring, subsequently triggering positive (negative) SST anomalies in the central Pacific through the wind-evaporation-SST feedback. The central Pacific SST anomalies, intensifying from summer to autumn, lead to a basin-uniform circulation anomaly over the WNP and ultimately control the WNP TCGF. Conversely, in the other two periods, owing to the northward shift of the NAJS, the influence of the NAO is constrained to the extratropics, thereby disrupting the linkage between the NAO and TNA SST anomalies. As a result, the interannual relationship of spring NAO with the WNP TCGF weakens. The decadal meridional shift of the NAJS is supposed to be associated with the phase transition of the Pacific Decadal Oscillation.
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