A statistical analysis is performed on kilometer scale horizontal velocity field fluctuations retrieved from single-Doppler lidar data. The retrieval technique is based upon assimilating Doppler lidar measurements of radial velocity from a series of low elevation angle plan-position indicator scans into a spectral vorticity model. The model assumes non-divergent, neutrally stable flow and employs a simple K-model for parameterization of sub-grid-scale effects. The retrieval techniques treats the coefficient of eddy diffusion, mean velocity and the initial conditions of the Fourier amplitudes of the fluctuational velocity field as adjustable model parameters. The end result of an assimilation run produces the time dependent spectral coefficients of the velocity field.
The data used for this study corresponds to a strong chinook event as observed by a ground based Doppler lidar near Colorado Springs, CO, USA, in March of 1997. The retrieved horizontal velocity fields reveal a complexity of coherent structures superimposed upon the mean flow.
Space and time dependent velocity autocorrelation functions of the retrieved fluctuational velocity fields are used to determine: 1) phase velocities associated with spatially coherent structures or modes, 2) average eddy propagation speed, 3) advective kinetic energy fluxes associated with the various scales of motion, and 4) the temporal decorrelation in a mode which occurs as a result of dissipation and energy transfer to other modes. Phase velocities and average eddy speeds are compared to the mean flow velocity. Also, the extent to which Taylor's hypothesis applies in this case is addressed