Observations of the Diurnal Evolution of the Lower Boundary Layer in a Subtropical Environment Using a Small Unmanned Aerial System (sUAS)

Energy and moisture transfers between the surface and the lower atmosphere play a critical role in the development, maintenance, and evolution of meteorological characteristics within the planetary boundary layer (PBL). The efficiency of these transfers, as well as the distribution of heat and moisture within the lower atmosphere, are largely defined by the vertical structure of the PBL; however, the inherent coupled feedbacks between the surface and the PBL leads to considerable complexity in diagnosing and predicting surface-based weather features. The fact that processes within the PBL are predominately local-scale, with rapidly varying spatial and temporal characteristics, makes real-time observations extremely important. To this end, in situ measurements of PBL structure and processes are critical in defining the scale and strength of energy and moisture gradients, and must be obtained to improve understanding of these processes for enhancing short-term weather prediction. For this project, a small fixed-wing unmanned aerial vehicle (UAV) with an embedded suite of weather sensors (together referred to as an unmanned aerial system [UAS]) will be used to measure temperature, humidity, and pressure over an active agricultural site in northeast Mississippi for the purposes of defining the evolution of PBL structure within a diurnal cycle over a vegetated landscape. The measurement missions will utilize a geographically consistent flight path such that the UAV will measure the defined atmospheric characteristics over the same spatial extent at 100’ intervals from the surface up to 1000’ (the maximum allowed operating altitude of the UAV platform). Flights will be conducted every two hours from 8:00am – 8:00pm local time on days with benign synoptic conditions to minimize turbulent mixing due to frontal influences. The results of this study will provide information regarding the variations in structure of the lower PBL over the course of a day, which will aid in both the theoretical descriptions of the PBL over a subtropical landscape. Additionally, the small UAS platform (including the UAV, meteorological sensors, and flight control equipment) can be further tested and refined to help solidify the technology for future atmospheric research and operational applications.