Effect of spring Tibetan Plateau snow cover on the frequency of intense tropical cyclones over the western North Pacific

Abstract

Tibetan Plateau snow cover (TPSC) is recognized as a critical driver in modulating the regional atmospheric circulation. However, the critical role of TPSC in the frequency of intense tropical cyclones (ITCs) over the western North Pacific (WNP) remains poorly understood. Based on the observed and reanalyzed datasets during 1979–2023, this study reveals a seasonally-lagged negative relationship between spring (March–April) TPSC and the frequency of ITCs over the WNP during the following peak season of ITCs (July–November). The analyses suggest that the sustainable hydrological effect of March–April TPSC enhances the upper-level convection heating and in turn intensify the South Asian High until July–November. Then, the Rossby wave trains are excited, inducing a baroclinic structure with anomalous upper-tropospheric cyclone and lower-tropospheric anticyclone over the WNP. The resultant changes in the ITC-related dynamic factors, including enhanced vertical wind shear and suppressed mid-tropospheric vertical motion, create an unfavorable environment for the genesis of ITCs. Meanwhile, the low-level absolute vorticity and mid-level meridional shear of zonal wind associated with the anomalous large-scale circulation further inhibit the intensification of tropical cyclones (TCs). Here, a physics-based statistical prediction model for the frequency of ITCs over the WNP is developed by incorporating spring TPSC and other factors. The model shows a robust predictive skill, with a correlation of 0.68 between the predictions and observations during 1979–2023. All this highlights spring TPSC as an important upstream modulator of the ITC activity over the WNP, providing the mechanistic framework and seasonal forecasting model for the frequency of ITCs over the WNP.