Unmanned Systems and Distributed Sensing Enable High Resolution Profiling Through the Morning and Evening Transitions

As micrometeorological research shifts to increasingly non-idealized environments, the lens through which we view classical atmospheric boundary layer theory must also shift to accommodate unfamiliar behavior. This shift in perspective requires new measurements. Atmospheric flows in complex settings and in transitional moments are often difficult to characterize, in part, because traditional measurement techniques have insufficient temporal and spatial resolution to resolve or locate the most critical atmospheric motions. That is, we know features should exist, but we don't know where they will be at any given moment. Static, point based measurements of atmospheric motion are insufficient in this regard. One path forward is a high resolution distributed measurement technologies. We will present the results of three intensive observation campaigns where a distributed temperature sensing device was suspended from an unmanned aerial platform during morning and evening transitions. The temperature measurements have a resolution of 0.15m and 1s respectively. Refinements of the DTS-UAS technique for atmospheric profiling will be shown and vetted. Humidity profiles are measured with a wet bulb-dry bulb technique. Wind speed is measured with a heated fiber optic cable device. All measurements have the same native high resolution that represents a 4 orders of magnitude increase in the data density over traditional approaches. The profiles cover a vertical extent of 100m with flights of 20-40 minute duration. These observations illustrate that the morning transition is initiated from aloft. Warm air sweeps downward to break the strong stable stratification. These mixing processes initiate unstable wave modes that have wave numbers predicted by Kelvin-Helmholtz theory. In addition, Monin-Obuknov theory is confronted with a wealth of new data in challenging environments. Profiles of sensible heat flux, evaporation and gradient Richardson number will also be presented.