Evolution of Early Morning Transition Periods using Uncrewed Aerial Systems

Uncrewed Aerial Systems (UAS) are now being routinely used not only for sampling atmospheric boundary layer (ABL) processes and land-atmosphere interactions but also have significant potential to improve weather forecasting at National Weather Service (NWS) Weather Forecast Offices (WFO). In the present study, we used observations obtained from a Meteomatics Meteodrone SSE UAS flown on 29 days between August and December 2020 at a site near Oliver Springs, Tennessee, located about 40 km northwest of Knoxville, Tennessee. During these UAS flights, we flew the UAS up to 700 m above ground level, starting around sunrise and continuing every half hour until 3.5-4.0 hours past sunrise under synoptically quiescent, fair weather conditions. Not only were these datasets provided in near-real time to the local NWS WFO in Morristown, Tennessee and used by forecasters there to assist with short-term operational forecasting needs, the UAS profiles provided a high-resolution view of the evolution of the early-morning transition (EMT) and how this evolution varies seasonally. We quantify the evolution of the EMT by using the UAS observations to compute the ABL height and, using the changes in the temperature and moisture fields, derive profiles of sensible and latent heat flux, respectively. We then discuss causes for the day-to-day variability of these fields and evaluate how well an operational weather forecast model, i.e. the High-resolution Rapid Refresh (HRRR) model, represents this variability. Lastly, we describe how continuing to perform frequent vertical profiles with UAS not only provides additional insights into the physical processes occurring within Earths ABL, but also is an important step toward using UAS observations to improve short-term weather prediction.