Direct Observations of Surface Fluxes and Air-Sea Exchange Coefficients in Low Winds Using a Small Uncrewed Aircraft System

In the marine boundary layer, the exchange of momentum, heat, and moisture occurs between the atmosphere and ocean. The efficiency of these air-sea exchanges can be determined by their respective coefficients, C_D, C_H, and C_E. Since it is too dangerous for a crewed aircraft to fly close to the ocean surface to directly obtain turbulence measurements used to calculate the exchange coefficients, a sUAS (small Uncrewed Aircraft System) is one of the only viable options. In March of 2023 a Black Swift Technologies S0 sUAS was deployed from the NOAA P-3 on a calm clear day in the Gulf of Mexico. The results from the data collected on the March 2023 flight were generally in good agreement with previous studies regarding exchange coefficients. Expanding on the research conducted in March 2023, a stepped descent in clear air from roughly 1500 m to 10 m was conducted in March of 2024 again, using the Black Swift Technologies S0. Previously in March 2023, only the last remaining 23 minutes were used for calculating the exchange coefficients. However, in March 2024, approximately 90 minutes of data was collected while conducting the stepped descent. The results from the clear air stepped descent will show that the use of sUAS, specifically the Black Swift S0 can be a viable option for improving the understanding of air-sea interactions and of flux profiles in the hurricane boundary layer.