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Abstract

The solar impacts on the tropical Pacific climate have been widely reported. But few studies focus on the effects of solar activity on the tropical cyclone (TC). In this study, the solar modulation on TC frequency over the western North Pacific in different solar cycle phases is investigated using observational and reanalysis data from 1979 to 2020. Results suggest that the responses of TC frequency to solar activity are obviously asymmetric in the high and low solar activity years (HS and LS). Specifically, the intensified solar activity could markedly induce more TCs in HS, however, no significant modulation can be found in LS. Further exploration reveals a possible air-sea coupled mechanism for this interesting phenomenon. The relatively cloud-free area in the western North Pacific could avail more incoming solar radiation at surface in HS than that in LS. This increased regional surface net solar radiation in HS could produce stronger surface upward latent heat flux and thus greater evaporation. Along with that, the local upward motion is dramatically enhanced over the TC source sector. Then for compensation, the regional sea level pressure is reduced and the low-level winds become cyclonic over the TC origin. All of these solar-caused regional anomalies in atmospheric circulation in HS contribute to more TCs over the western North Pacific. The key of this possible mechanism is that the regional increased solar forcing at ocean surface in cloud-free area could be amplified by the regional strengthened upward latent heat flux and evaporation in the TC source.