SIMULATION OF TROPICAL CYCLONE 201610 (LIONROCK) AND ITS REMOTE EFFECT ON HEAVY RAINFALL IN HOKKAIDO

抄録

 When tropical cyclone (TC) 201610, namely Lionrock, was moving over the western North Pacific from southeast of Honshu to cut across the Tohoku region during 29-30 August 2016, continuous and intense rainfall occurred in mid- to southeastern Hokkaido, far from the TC center. The Weather Research and Forecast (WRF) model is used to investigate the possible remote effect of TC Lionrock on this heavy rain in Hokkaido. The National Center for Environmental Prediction (NCEP) global final (FNL) analysis is used to provide both the initial and lateral boundary conditions for the model. Three numerical experiments are performed. In the control experiment (CTL), the original FNL is used. In the no-TC experiment (NoTC), the vortex associated with TC Lionrock in the FNL is removed such that the TC signal does not appear at the initial time. In the no-topography experiment (noTopo), the terrain height over Hokkaido set to 1 m if it is higher than 1 m. As verified against observations, the CTL and noTopo experiments capture reasonably well the TC track. The CTL experiment also reproduces relatively well the spatial distribution and temporal evolution of rainfall, whereas the remote rainfall in Hokkaido is largely suppressed in the noTC experiment, suggesting a significant far-reaching effect of TC Lionrock. The combined effect of Lionrock and the stationary low-pressure system located over the Sea of Japan enhances the moisture transport towards Hokkaido through their outer circulation. Particularly, only very small amount of rainfall is observed in Hokkaido in the noTopo experiment, indicating that the orographic forcing of the southeastern mountains in Hokkaido plays the most critical role in this extreme rainfall event.