A vortex model of winds associated with clear-air turbulence is shown to be useful for characterizing actual airline encounters with severe turbulence. The model consists of an array of vortices with solid-body cores embedded in a potential flowfield. Parameters such as the size and strength of the vortices and their locations are identified using a modified Newton-Raphson algorithm. A manual identification startup scheme is used to minimize errors in the initial parameter estimates, and the identification algorithm is found to be robust in regard to the remaining errors. The analysis of a turbulence experience involving a commercial airliner demonstrates the success of the model and estimation procedure. The analysis finds vortices with core diameters of 1000 ft and tangential velocities of 87 ft/s in this encounter. LEAR-air turbulence (CAT) is a little-understood phenomenon that occurs in the mid to upper troposphere and the lower stratosphere and that poses a safety hazard to aircraft. The most severe cases are characterized by sudden, violent disturbances with definite periodicity. This problem is being investigated by the NASA Ames Research Center in con- junction with the National Transportation Safety Board. Because of the small scale in both duration and distance over which CAT occurs, it has been a difficult phenomenon to study. However, in the recent past, wide-bodied commercial aircraft equipped with digital flight-data recorders have had a few encounters with CAT, and the data from these recorders, along with additional data from air-traffic control (ATC) radar records, have made it possible to obtain a detailed description of the winds associated with CAT encounters. A model of the wind environment during CAT has been developed using these wind data and previous theoretical studies of CAT. These studies1'6 predict that CAT is a result of the breakdown of stably stratified shear layers in the at- mosphere, a condition known as Kelvin-Helmholtz instability. The shear layers roll up into a vortex array which forms in a Kelvin cat's eyes pattern (Fig. 1). The direction of rotation of the vortices depends on the way the shear layer breaks down, as discussed in Ref. 7. To compare /theory with data from actual encounters, parameter-identification techniques have been used to match the winds produced by a vortex-array model to the data. This has been done successfully with two actual encounters and is reported in a previous paper.7 A similar technique had been used earlier to study an airplane's traling vortices.8 The pur- pose of this paper is to describe the vortex model and the parameter-identification techniques used to match the model to the winds found in a CAT encounter. First, a vortex model and its relation to an aircraft flight path is described. Next, the algorithm used to determine the model parameters is discussed briefly, followed by an explana-