Oklahoma weather phenomena that may affect aviation

Abstract

We report here the latest studies by the National Severe Storms Laboratory of interest to the aviation community. Of particular importance are turbulence produced by storms, low-altitude wind shear in storm outflows, and downdrafts and gust fronts. Storm turbulence has been studied extensively with the help of Doppler radar. Comparison of spatial spectra of longitudinal and transverse velocities has revealed that in severe storms the outer scale of turbulence is at least 2 km. Because of this and because measurements of spectrum widths at two different viewing angles agree, the width could prove a good indicator of storm turbulence that may affect aircraft. We report on the asymmetry of low-altitude divergent outflows produced by downbursts in Oklahoma. This has implications for the detection and quantification of these phenomena with pulsed Doppler radar. Gust front shears estimated by Doppler radar (at heights between 50-600 m) average 1.6 times the shear measured a few meters above the surface. Tall tower data show that both wind speed and wind shear increase in the lowest 90 m of the atmosphere. Thus, surface-based anemometers considerably underestimate wind shear just 100 m or so above the surface. Doppler radars located near airports may allow measurements at such low altitudes and resolve significant wind shears. Automatic methods to detect, track, and extrapolate shear produced by waves and gravity currents (downbursts) are being developed, and some results are shown.