The impacts of surface drag coefficient on the intensification and energetics of Typhoon Megi (2010)

This study is part of our work on the impacts of PBL parameterizations on simulated Typhoon Megi (2010) at 2-km resolution using the nonhydrostatic model of the Japan Meteorological Agency and Meteorological Research Institute. The current study varies the surface drag coefficient (Cd) in the Deardorff scheme and examines its effects on the intensification and energetics of an actual TC. Increasing Cd intensifies the secondary flow which in turn enhances kinetic energy (KE) conversion. However, it also weakens the tangential winds at the lower level as it strengthens the mean-radial flow of absolute angular momentum. As a result, more AAM dissipates near the surface and, hence, KE. The energy gain is overweighed by a larger frictional loss that leads to a weaker cyclone. The opposite impacts are found when Cd is decreased. Reducing surface drag decreases energy conversion and delays intensification. On the other hand, the energy loss is also decreased and after 3-days integration, the TC rapidly intensified. Further discussion on the mechanism by which energy is gain and loss due to surface drag will be explained during the conference.