MESOSCALE OCEANIC RESPONSES TO TYPHOONS IN THE NORTHWESTERN PACIFIC

Abstract

 Typhoons alter the upper ocean dynamics and thermal structure, giving rise to feedback on the atmosphere. Intense ocean surface wind and barometric effects induce rough waves and storm surges that occasionally cause severe coastal disasters. For rigorous oceanic modeling under typhoon conditions, we implement the inverse barometer effect and the COAMPS bulk formula into ROMS. A submesoscale eddypermitting oceanic modeling is configured at a horizontal resolution of 2 km based on the JCOPE2-ROMS downscaling system forced by the JMA GPV-MSM atmospheric reanalysis. A retrospective, synoptic reanalysis is carried out with a particular focus on the two consecutive super typhoons Phanfone (#1418, Category 4, the lowest pressure was 935 hPa) and Vongfong (#1419, Cat. 5, 900 hPa) in the fall 2014. These typhoons abruptly amplify the volume outflux from the Seto Inland Sea (SIS) at the Bungo Channel, leading to the pronounced counter-clockwise circulation that opposes the clockwise overall SIS circulation under the normal condition. The model also successfully reproduces increased eddy kinetic energy below the typhoons with intense cyclonic positive vorticity driven by torque of the wind stress curl, not only at surface but also at depth down to about 100 m deep. These cyclones are cold-core mesoscale eddies with SST decrease by about 3°C associated with prominent mixed layer deepening.