Surface Drag Coefficient Observations in Western North Pacific Tropical Cyclones

Abstract Surface momentum flux and drag coefficient are critical factors influencing the structure and intensity of tropical cyclones (TCs). However, due to limited measurements, the behavior of these quantities, particularly in TCs over the western North Pacific (WNP), is not fully understood. Here we analyze observations from dropsondes and radiosondes in 141 WNP TCs in 2009–2024. We find that over the deep and open South China Sea (SCS), the drag coefficient increases with wind speed until reaching 1.5 × 10 −3 at a threshold wind speed of 30 m s −1 , then levels off or decreases above this wind speed. A quadrant analysis further reveals that the drag coefficient is significantly higher in the left‐front storm quadrant than in the right‐front and rear quadrants at wind speed around 30 m s −1 . Over the urban area, the drag coefficient is about 10 2 times higher than the open ocean and does not show significant variation with wind speed up to 25 m/s. These observations can inform the surface flux parameterizations used in TC modeling, prediction, and hazard assessment.