Joint agency turbulence experiment

Description

Doppler radar and aircraft data acquired during the 1981 and 1982 observation seasons are discussed. Time histories of Doppler radar mean velocity and spectrum variance data acquired while tracking an instrumented aircraft during 34 thunderstorm penetrations are presented. Time histories and analysis of turbulence severity, as determined from these radar and aircraft data, are also presented. Whereas use of radar mean velocity in structure function analysis results in underestimation of the actual turbulence severity, radar methods based upon Doppler spectrum variance successfully detect regions of turbulence hazardous to aircraft. The variance-based method, employing a modeled turbulence energy spectrum with a maximum finite eddy size, is found most effective when the turbulence outer scale lies in the range of 1-4 km. Classification of turbulence severity as light, moderate, heavy, or severe with a single outer scale value was unreliable. However, classification into composite severity classes, where a composite class combined two or more individual severity classes, was found to be a successful approach for locating hazardous and nonhazardous turbulence regions. Data also show Doppler spectrum variance to be poorly correlated with shear of the radial wind. This shear, resulting from nonturbulence storm structure generally contributed less than 10 % of the turbulence contribution to Doppler spectrum variance and could generally be neglected when estimating turbulence severity.

Subjects