| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4551997 | Ocean Modelling | 2015 | 20 Pages |
•We examine the radius of Haiyan that affects surges and waves in the Leyte Gulf.•We propose the method of leveling the wave dependent drag off at high winds.•Leveling off at 25 m/s is suggested for the Haiyan surge and wave in the Leyte Gulf.•Leveling off in a coupled surge and wave model is crucial in extremely high winds.
The present study investigates how the wind speed-limited wave dependent drag coefficient (CD) influences the surge and wave generation of Super Typhoon Haiyan, which struck the coasts of the Leyte Gulf, in the Philippines (2013), using a coupled surge and wave model. In addition, we examine the effect of changes of the radius (Rmax ) at which the maximum wind speed occurs. Accurate determination of this radius is crucial to the Haiyan wind and pressure field when using a parametric wind and pressure model because of lack of observation data. The calculation results show that the radius ranges from 40 km to 50 km: as the radius becomes narrower, the surge and wave heights are reduced. Our calculation of surge and wave levels uses a modified version of Janssen’ method (Janssen, 1989, 1991) with a step function applied to level off CD in the exponential wave growth term. In the present method, the wind speeds are limited to a certain threshold; below this value the effective roughness is estimated with a logarithmic wind profile. With the newly modified method, we investigate the effect of the wind speed-limited wave dependent drag CD for high winds (<70 m/s) on the Haiyan surge and wave levels. When leveling off CD at 25 m/s for Rmax=50km good agreement with survey data is obtained in terms of surge level (6.5 m) and wave heights (7 m and 17 m inside and outside of the gulf). The numerical experiments suggest that leveling off at wind speeds of 25–30 m/s results in the accurate prediction of Haiyan storm surge and wave levels in the coupled surge and wave model. The study demonstrates the applicability of the present method of leveling off at wind speeds of 25–30 m/s in a coupled surge and wave model for super typhoon conditions.
