Impact of the winter Arctic sea ice anomaly on the following summer tropical cyclone genesis frequency over the western North Pacific

This study examines the impact of the winter Arctic sea ice concentration (ASIC) anomaly on the succedent summer tropical cyclone genesis frequency (TCGF) over the western North Pacific (WNP) and provides a new insight into the underlying physical mechanisms. There is a significant time-lagged relation between winter ASIC anomalies over Greenland-Barents-Kara (GBK) seas and the following summer TCGF over the southeastern part of the WNP. This delayed association is attributable to large-scale circulation anomalies and the air-sea interaction processes over the North Pacific induced by the winter ASIC anomalies. Specifically, a higher winter ASIC over the GBK seas induces an atmospheric wave train that propagates southeastward to the North Pacific. The associated cyclonic anomaly over the mid-latitude North Pacific is accompanied by southwesterly wind anomalies over the subtropics and results in sea surface temperature (SST) warming by reducing upward surface heat fluxes. This SST warming is maintained and further extends southward to the tropical Pacific in the following summer via a wind-evaporation-SST feedback, which in turn forces overlying atmospheric circulation via a Gill-type atmospheric response, including a pair of cyclonic and anticyclonic anomalies in the low- and upper-level troposphere, respectively, over the WNP. These atmospheric anomalies favor TC genesis over the southeastern part of the WNP by decreasing the vertical wind shear and increasing the convection, low-level vorticity and humidity. The above processes apply to the years when lower ASIC winters are followed by decreased TC genesis over the southeastern part of the WNP except for opposite signs of SST and atmospheric circulation anomalies. This study suggests that the winter ASIC anomaly over the GBK seas is a potential predictor for the prediction of the WNP TCGF in the following summer.