Influential role of inter‐decadal explosive cyclone activity on the increased frequency of winter storm events in Hokkaido, the northernmost island of Japan

Abstract

This study examined explosively developing extratropical cyclone activity in the vicinity of Japan in boreal winter from 1979/1980 to 2016/2017 mainly using the Japanese 55‐year Reanalysis data. The in situ observation and reanalysis data revealed increased frequencies of both strong winds and heavy precipitation in Hokkaido, the northernmost island of Japan, after the end of the last century, which is consistent with the fact that the cyclones migrating along the Kuroshio Current (KC cyclones) have tended to approach the Hokkaido region in recent years. To examine factors controlling the cyclone track and rapid development, we performed composite analyses of the northwards migrating type (N type) and eastwards migrating type (E type) KC cyclones. In the N‐type cyclone, wave trains prevailed along the polar front and subtropical jets over the Eurasian continent, thereby forming an upper‐level trough (ridge) to the west (east) of the cyclone. An upper‐level divergence accompanied by rapid development of the N‐type cyclone excited wave packets downstream as a Rossby wave source, leading to further reinforcement of the upper‐level ridge east of the cyclone. The anomalous anticyclone with a barotropic nature is capable of forcing the cyclone track to shift northwards. Furthermore, a combination of the N‐type cyclone and the anomalous anticyclone to its east facilitates moisture import into the cyclone system from lower latitudes, contributing to enhanced moisture flux convergence. In reality, diabatic heating in the vicinity of the cyclone centre is larger in the N‐type cyclone than in the E‐type one. It is also suggested that the pronounced Rossby wave propagation along the subtropical jet related to a climate regime shift in the Tropics is responsible for the recent increase in the number of N‐type cyclones.

Contributions of the climate regime shift and historical global warming to explosive cyclone activity around Japan according to large‐ensemble simulations

“…The downstream development of wave packets causes the formation of a ridge with a barotropic structure east of Japan that is able to force the northward shift of the KC cyclone, according to Tsukijihara et al (2019). 3.…”

“…Tsukijihara et al . (2019, hereafter T2019) focused on inter‐decadal explosive cyclone activity and possible interaction between the wave trains and explosive cyclones. They examined explosive cyclone activity around Japan in boreal winters from 1979/1980 to 2016/2017, mainly utilizing the Japanese 55‐year Reanalysis (JRA‐55) data (Kobayashi et al ., 2015).…”

Estimation of water origins within an explosive cyclone over the Sea of Japan using an isotopic regional spectral model

“…To evaluate the IsoRSM model, precipitation was sampled diurnally for stable isotopic analysis on the roof of the administration building at the Faculty of Environmental Earth Science, Hokkaido University, in Sapporo, northern Japan, where extratropical explosive cyclones approach frequently (e.g., Tsukijihara et al 2019). Rainfall samples were collected using a funnel with a polyethylene vessel, whereas snow samples were collected in a bucket and melted in a plastic bag at room temperature.…”

High-Rate Precipitation Occurrence Modulated by Solar Wind High-Speed Streams

“…A tracking algorithm on the surface low pressure field from the JRA-55 meteorological re-analysis data [40] was applied and tracks of explosive extratropical cyclones in the North Pacific were obtained [24]. Those considered in Figure 1 reached minimum central pressure < 990 mb and maximum normalized deepening rate NDR r > 0.5.…”