Connection between the genesis number of tropical cyclones over the western North Pacific and summer rainfall over Northeast Asia

Since a tropical cyclone (TC) usually accompanies a large amount of rainfall, it is estimated that average amounts of rainfall in summer increase in Northeast Asia (NA) when the genesis of TC in the western North Pacific (WNP) is frequent. However, the present study found a negative correlation between TC genesis number in summer over the WNP and the amount of summer rainfall over the mid-latitudes of NA from 1980 to 2009. The results of the analysis reveal that in a positive TC genesis phase (years in which TCs occur more frequently than on average), an anomalous cyclone forms over the WNP, which generates anomalous cold and dry northeasterly winds in the mid-latitudes of NA, resulting in reduction of rainfall. In comparison, in a negative TC genesis phase (years in which TCs occur less frequently than on average), a large anomalous anticyclone develops over the western Pacific, which generates anomalous warm and humid southwesterly winds, resulting in increase of rainfall in the same region. The comparisons of the TC tracks between the two phases also reveal that in both phases, the TC passage number is rather low in the mid-latitudes of NA regardless of TC activities over the WNP. This suggests that TC number does not greatly affect the total amount of summer rainfall in NA; instead, a large-scale atmospheric circulation forming favorable (unfavorable) rainfall conditions in the negative (positive) TC genesis phase controls the summer rainfall in that area.