The Case of Sharp Velocity Transitions in High Vertical Wind Shear When Measuring Doppler Velocities with Narrow Nyquist Intervals

Abstract

n investigation was launched following unexpected observations of step-function transitions in Doppler velocities from scanning radars in regions of high vertical wind shear. It revealed that, if wind velocity transitions are sufficiently sharp and strong, then the measured velocity at each pulse repetition frequency undergoes an unusual smooth transition, from being in the right Nyquist interval to being in the wrong one. Hence, when these velocities are dealiased, a step function in velocity appears at the transition between where velocities were aliased and where they were not. The extent and the impacts of this data artifact are considered.