Response of rapidly developing extratropical cyclones to sea surface temperature variations over the western Kuroshio–Oyashio confluence region

Abstract

The dynamical response of rapidly developing extratropical cyclones to sea surface temperature (SST) variations over the western Kuroshio–Oyashio confluence (WKOC) region was examined by using regional cloud‐resolving simulations. This study specifically highlights an explosive cyclone that occurred in early February 2014 and includes a real SST experiment (CNTL run) and two sensitivity experiments with warm and cool SST anomalies over the WKOC region (warm and cool runs). The results derived from the CNTL run indicated that moisture supply from the ocean was enhanced when the dry air associated with the cold conveyor belt (CCB) overlapped with warm currents. Further, the evaporated moisture contributed substantially to latent heat release over the bent‐back front with the aid of the CCB, leading to cyclone intensification and strengthening of the asymmetric structure around the cyclone's center. Such successive processes were more active in the warm run than in the cool run. The dominance of the zonally asymmetric structure resulted in a difference in sea level pressure around the bent‐back front between the two runs. The WKOC SST variations have the potential to affect strong wind distributions along the CCB through modification of the cyclone's inner system. Additional experiments with two other cyclones showed that the cyclone response to the WKOC SST variations became evident when the CCB north of the cyclone's center overlapped with that region, confirming that the dry nature of the CCB plays an important role in latent heat release by allowing for larger moisture supply from the ocean.

Significant Impact of Heat Supply From the Gulf Stream on a “Superbomb” Cyclone in January 2018

“…On the other hand, the SLP structure around the cyclone center was symmetric in the NSLH run owing to the weak LH (Figure b). These results agree with those of Hirata et al (). It is conceivable that the difference in the inner structure of the cyclone led to the difference between the tracks in the two runs in Figure b.…”

Ocean Observations in Support of Studies and Forecasts of Tropical and Extratropical Cyclones

“…While these atmospheric and ocean conditions are mostly linked with the number of ECs developing, the strength, intensification and trajectory of the ECs are known for being directly influenced by upper ocean conditions (Kuwano- Yoshida and Minobe, 2017), with their genesis often associated with oceanic frontal systems. For example, the maximum frequency of explosive cyclogenesis and deepening is found to occur near the Kuroshio or the Gulf Stream; these oceanic western boundary currents are associated with large heat fluxes from the ocean to the atmosphere (Sanders and Gyakum, 1980;Ulbrich et al, 2009;Hirata et al, 2015Hirata et al, , 2016Hirata et al, , 2018Kuwano-Yoshida and Minobe, 2017). Future projections suggest that strong ECs will tend to increase, while the total number of ECs is expected to decrease (Colle et al, 2015;Chang, 2017).…”

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

“…Rapid development of the cyclones requires not only baroclinic instability but also vertical coupling between an upper‐level disturbance and a surface cyclone (e.g., Hoskins et al, ; Takayabu, ; Shapiro et al, ) and diabatic heating around the cyclone centre (e.g., Kuo et al, ; ; Reed et al, ; Kuwano‐Yoshida and Asuma, ). Latent heat release within the cyclone system through the warm conveyor belt (WCB) contributes to the cyclone intensity because the WCB facilitates water vapour import into the cyclone from low latitudes (e.g., Carlson, ; Booth et al, ; Madonna et al, ; Binder et al, ), whereas a positive feedback process between the cold conveyor belt (CCB) and latent heating over the bent‐back front also contributes to cyclone development through heat and moisture supply from mid‐latitude warm currents (Hirata et al, ; ; ).…”