Surface Layer Drag Coefficient at Different Radius Ranges in Tropical Cyclones

Using dropsonde data and a flux-profile method, this study investigates the drag coefficient (Cd)–wind speed relationship within different radius ranges. The results show a systematic decrease of friction velocity u* from the range of R/RMW > 1.05 to that of R/RMW 1.05 or R/RMW −1 can be obtained. However, the roll feature becomes vague in the ranges of R/RMW Cd of R Cd of R −1, u* of R < 0.75RMW is significantly larger than that of R < 0.85RMW. This phenomenon is also linked to the TC dynamics (e.g., the large radial gradients of winds and the drastic vertical variation of the bulk Richardson number), but the speculation needs to be verified in future study