Abstract
Warm western boundary currents are associated with increased convective precipitation events, which are, in turn, conducive to the occurrence of lightning. The East Asian monsoon regions, which experience high rainfall, also experience high levels of lightning. Japan is unique in that both of these factors affect the frequency of lightning. However, despite the high population density and potential for natural disasters, the spatiotemporal variations in lightning occurrence around the country have not been clarified to date. Here we show that the incidence of lightning is influenced by the Kuroshio path system, which conveys tropical heat to the midlatitude regions of the western Pacific and ranks among the world’s strongest warm ocean currents. Specifically, we show that the Kuroshio Large Meander affects both the mean annual frequency and the interannual variation in lightning occurrence. Lightning is more likely to occur in areas with high sea surface temperatures (SSTs) than in areas with relatively low SSTs. Warm oceans, which supply large amounts of water vapor and heat, favor the development of lightning. The abundance of winter lightning, another peculiarity of Asian winter monsoon regions, is also linked to the Tsushima Warm Current, which flows through the Sea of Japan and has its source in the Kuroshio. The temperature difference between the sea surface and the mid-troposphere, an indicator of potential instability associated with vertical deep mixing, is also a good predictor for lightning occurrence and the interannual variations therein. Similar relationships may exist in other oceans, particularly in other western boundary currents.
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