LAUSR

Using the Database for Policy Decision‐Making for Future Climate Change (d4PDF), this study examined the impact of a tropical climate regime shift around 1998/1999 on explosive cyclone activity around Japan in boreal winter, highlighting cyclones moving along the Kuroshio Current (KC cyclones), especially northward‐migrating (N‐type, as defined in Tsukijihara et al., 2019) KC cyclones. Wave‐train patterns along the Asian jet affect the track and rapid development of N‐type cyclones, and the frequency of the top 10% of pronounced wave‐train patterns using a teleconnection index (NI10%) has increased since 1998/1999. Tropical precipitation in the region close to the Bay of Bengal increased with the climate regime shift, leading to the increased frequency of NI10%. The downstream development of wave packets tends to form a ridge with a barotropic structure east of Japan that is able to force the northward shift of the KC cyclone. In reality, there are high correlations between the inter‐annual variations in the ensemble mean frequencies of NI10%, N‐type cyclones, and tropical precipitation around the Bay of Bengal, and all three indices have increased since 1998/1999. Furthermore, the above results are nearly the same in both historical and non‐warming experiments, indicating that recent changes in the frequency of N‐type cyclones are not directly related to historical global warming.