[A-AS03] 台風研究の新展開～過去・現在・未来

[AAS03-09] Climatology of Tropical Cyclone Seeds and Survival Rates to Tropical Storms

*池端 耕輔¹、佐藤 正樹¹ (1.東京大学大気海洋研究所)

キーワード：台風、台風の種、生存率

A mechanism behind the variation of tropical cyclone (TC) genesis frequency can be understood more deeply by focusing on tropical cyclone seeds (TC seeds). Previous studies indicate that the change in the number of TCs due to global warming is primarily explained by that of TC seeds. However, the validity of such a relationship is not clarified on monthly or yearly variations in the present climate. In this study, we examine the relationship between TC seeds and TC genesis, and underlying factors for survival rates to TC. Tracks of weak lower tropospheric vortices are extracted as TC seeds from the reanalysis ERA5 during the period of boreal summer from 2000 to 2018. Survival rates, the ratios of developing TC seeds to the sum of developing and non-developing ones, are then calculated by comparing with TC observations. Horizontal distributions and subseasonal to annual variations of TC seeds genesis frequency and survival rates show that the main factor influencing TC genesis frequency is survival rate, with the number of TC seeds also having secondary effects. Local variations of TC seeds genesis frequency positively correlate with mean values of low-level relative vorticity related to large-scale wind fields. On the other hand, survival rates change with surrounding atmospheric conditions at an early stage after TC seed genesis. These results suggest that survival rates affected by environmental fields largely control subseasonal to annual variations of TC genesis frequency, while the integrated number of TC seeds changes relatively smaller in the present climate.