Uncrewed Aircraft System Measurements of Atmospheric Surface-Layer Structure during Morning Transition*

This study applies uncrewed aircraft systems towards the investigation of surface-layer structure during the morning transition.  Three uncrewed aircraft systems simultaneously measuring horizontal transects were partnered with a fourth measuring vertical profiles during two consecutive mornings as part of the Collaboration Leading Operational Unmanned Aerial System Development for Meteorology and Atmospheric Physics (CLOUDMAP) measurement campaign near Stillwater, Oklahoma, USA.  The results reflect differences in the evolution of spatial statistics, despite very similar synoptic conditions.  Conditional averaging was also applied to identify the structure of sweep and ejection motions and results revealed similarities to observations from canonical wall-bounded flow. Finally, it was found that these structures contribute approximately 20% to 30% of overall turbulence kinetic energy, momentum, and sensible heat flux, with an increase observed during the course of the boundary-layer transition.