Uncrewed Aircraft Observations of Turbulent Characteristics in the Low-Level Eye and Eyewall of Intense Hurricane Ian (2022)

Tropical cyclones (TCs) are one of the leading economically weather-related disasters in the world, however, predicting the intensity change and tracks of TCs remains a significant challenge. One of the primary reasons for this difficulty is the poor understanding of the planetary boundary layer (PBL) turbulent processes. This is mainly due to the rarity of in-situ high-resolution measurements of kinematic and thermodynamic properties in the low-level region of intense hurricanes. Over the past decade, an air-launched, small uncrewed aircraft system (sUAS) has been explored by NOAA to better sample the highly turbulent TC PBL. Hurricane Ian (2022), a Category 5 TC, was sampled by Anduril’s Altius 600 sUAS as it underwent rapid intensification just before landfall along the southwest coast of Florida. The sUAS collected data in a strong turbulent environment below 1.5 km altitude in both eyewall and eye areas with sUAS’s pitch, roll, and yaw values reaching 30^o. The sUAS extended its measurements from the eyewall to the cloud/clear eye region that is hard to sample by dual-Doppler radar on NOAA’s WP-3D aircraft. Spectral analysis shows the dominant scale of the organized eddies is in large-eddy scale in PBL (200 – 2000 m). Detailed analyses of turbulence structure using Ian data in comparison with data from Hurricanes Maria (2017) and Hugo (1989) are presented. Novel sUAS observations provide opportunities for a better understanding of the turbulent mixing process in the high-wind regime. The challenges of using sUAS data in TC conditions are also discussed.