Spatial Variability of Surface Drag Estimates within Tropical Cyclones in the Atlantic Basin

Momentum exchange between the atmosphere and ocean is important in determining tropical cyclone (TC) intensity change (i.e., rapid intensification), but there is uncertainty in the processes governing this exchange in high wind environments and how these processes may vary spatially within a TC. Previous research shows that surface drag has a direct relationship with wind speed, in that the surface drag coefficient increases as wind speed increases up to a certain threshold before leveling off or decreasing as wind speed continues to increase. Surface drag is also affected by wave characteristics, which vary across different regions of a TC based on the interaction between the ocean surface and the wind direction and direction of storm motion. To better understand the processes influencing surface drag in a TC and how these processes may vary across the storm due to wave characteristics, we estimate momentum flux across different quadrants and radial bands of Atlantic hurricanes utilizing atmospheric dropsondes from the TCDROPS database. Results show varying behavior of surface drag between the right and left sides of TCs as well as between the inner core and other regions of the storm. The difference in surface drag between spatial groups could be related to varying processes in different areas of the storm and/or varying wave characteristics. Understanding the reason(s) for such differences could advise improvements to the sampling scheme or suggest additional atmospheric and/or oceanic processes be considered in the calculation of surface drag and the total momentum flux.