The Impact of Observed Drag Reduction Over Land on Typhoon Forecasting

Abstract

AbstractThe surface drag coefficient plays a crucial role in determining the momentum exchange between the Earth's surface and the atmosphere. Previous studies have observed a tendency for the drag coefficient to decrease at high wind speeds over land, primarily due to the inverse energy cascade. This study aims to examine the impacts of the reduced drag coefficient on the typhoon forecasting skills in terms of the track, the central pressure, and the 10‐m maximum wind speed. Drag reduction is approached through the logarithmic wind profile and a new formula that considers the reduction in roughness length. The results show that the track and the 10‐m maximum wind speed forecasts are improved, but these improvements are primarily evident over plain areas, as the typhoon structure is significantly disrupted by the topography over mountainous areas. Additionally, the reduced drag coefficient results in less dissipation of the typhoon's wind fields over land. As the wind speeds at coastal areas are enhanced compared with those in operational model, the changes in the Coriolis force are responsible for the track prediction improvement. These findings highlight the importance of parameterizing coherent processes in current numerical models.