Using Coyote UAS Observations to Evaluate Large-Eddy Simulations (and Vice Versa)

The Coyote UAS (Uncrewed Aerial System) offers a unique opportunity to collect observations in the hurricane boundary layer (roughly, 0-1 km above the ocean surface). Measurements of turbulent fluctuations are ultimately needed to evaluate and improve the underlying assumptions of surface-layer and boundary-layer parameterization schemes in numerical weather prediction models. Coyote data collected in Hurricane Maria in 2017 demonstrate the potential of the Coyote system to obtain such data, including rare estimates of eddy dissipation rate in the hurricane boundary layer (see presentation in this session by R. Dobosy). However, these flights also clarified certain challenges for Coyote data collection, such as large turbulence intensity and gust factors in the lowest ~100 m of the hurricane boundary layer.

Another relatively new tool for analyzing turbulence in hurricane conditions is large-eddy simulation (LES), which uses grid spacing < 100 m to explicitly simulate turbulent fluctuations near the ocean surface. In principle, LES output could be used to evaluate boundary-layer parameterization schemes, although LES models are also dependent on certain assumptions, particularly near the ocean surface. The second half of this presentation will compare the measurements of turbulence intensity, gust factor, and eddy dissipation rate from the Coyote flights in Hurricane Maria to those produced by idealized LES with 10 m grid spacing. Although a key goal is to evaluate the LES output using Coyote observations, we will also show how LES output can help with the interpretation of UAS data and can guide the design of future Coyote flight patterns.