Physical Processes Leading to the Response of Extratropical Cyclones to Sea Surface Temperature Variations Around the Kuroshio Current

The Kuroshio Current is a western boundary current in the North Pacific Ocean and flows around the south of Japan. The path of the Kuroshio Current varies and often follows the large meander (LM) path to the south of Japan. The Kuroshio LM is associated with a cyclonic cold-core eddy, causing cold sea surface temperature (SST) anomalies. Previous studies suggested that the LM-induced SST anomalies affects the tracks and intensification of extratropical cyclones. However, our understating of dynamical processes related to the cyclone response to the LM remains limited. This study investigated physical processes related to the response of extratropical cyclones to the Kuroshio LM during winter by conducting cloud-resolving experiments. To examine the responses of the cyclones to the SST variations, we used SST distributions related to the Kuroshio LM and straight (ST) paths. We highlighted two cyclones (cases 1 and 2) moving around the south of Japan. Observation showed that precipitation was enhanced near the center of the cyclone in case 1, but not in case 2, as they passed through the LM region. This suggests that the role of diabatic processes in the cyclone response to SST anomalies is different in the two cases. In cases 1 and 2, the decrease in cyclone central pressure was suppressed in the LM run compared to that in the ST run. This suppression of the pressure was more pronounced in case 1 than in case 2. In addition, when passing near the LM region, the tracks of cases 1 and 2 in the LM run were south of the tracks of cases 1 and 2 in the ST run. Baroclinic processes contributed to the cyclone responses in cases 1 and 2, while diabatic processes contributed only to those in case 1. In both cases, the SST anomalies altered the near-surface baroclinicity, thereby influencing the responses via baroclinic processes. In case 1, the SST anomalies influenced the near-surface convective instability and the associated latent heating north of its center, ultimately influencing the responses via diabatic processes. In case 2, diabatic processes hardly affected the responses because it was not accompanied by latent heating near its center. These results suggest that the diabatic response to SST anomalies becomes significant when extratropical cyclones are associated with latent heating near their centers as they pass over the LM region, and this is related to the pronounced response of cyclones to SST anomalies associated with the Kuroshio LM.