Comparing Airborne Turbulence Measurements to NEXRAD-Derived Estimates

Turbulent airflows are known to exist in and around thunderstorms. Their presence has a direct effect on cloud evolution and structure, as well as aircraft safety. Research aircraft have been requested in a variety of field projects, as they provide a unique dataset that would otherwise be unattainable. When operating near active convective precipitation regions, the crews of these platforms must rely on experience and training to assess risks to the aircraft from turbulence. Providing further information of storm-induced turbulence from both operational and research Doppler radars would then be beneficial to both science objectives and crew safety.

The University of Wyoming King Air (UWKA) research aircraft was deployed in the Plains Elevated Convection At Night (PECAN) field experiment. One focus of the UWKA during this campaign was to sample bore and wave-like features generated by nocturnal convective systems. During the mission on 11 June 2015, the UWKA encountered a severe turbulence event after passing over an outflow boundary generated by a convective complex. The convective system was well sampled by the NEXRAD weather radar network, in addition to the in-situ measurements obtained by aircraft during this unique case. Eddy dissipation rates (EDRs), a measure of turbulent strength, produced from gust probe observations aboard the UWKA were compared to estimated EDR values for in-cloud turbulence from an algorithm using NEXRAD Doppler radar data.

Both sets of observations were integrated using the Airborne Weather Observations Toolkit (AWOT) and the Python Turbulence Detection Algorithm (PyTDA) software packages, both open-source distributed. This presentation will explore the immediate ambient environment leading up to and during the turbulence incident and compare the aforementioned measures of turbulent strength. It was found that the UWKA entered a sloping, elevated turbulent layer after crossing the primary outflow boundary. Extracting Doppler radar data and estimates to the aircraft track showed good agreement qualitatively between the measurements. Radar-based estimates were higher than those produced by aircraft measurements. Further work is being conducted on historical cases that coincide with Doppler radar observations on a number of airborne platforms. This will help aid EDR algorithm improvement as well as assess the effectiveness of aircraft safety warnings in future field campaigns.