Horizontal coherence decay near large mesoscale variations in topography.

Abstract

A surface layer experiment is described which includes measurements of turbulent velocities at 2 m above the surface with an array of newly developed drag anemometers. The experiment site is located in central Pennsylvania where mesoscale topographic irregularities exist. The presence of a low mountain ridge near the site affects the estimated lateral scale of turbulence and the fluctuations of the lateral velocity component. A good correlation has been found between the variance spectrum of the lateral (or crosswind) velocity component and an estimate of the lateral scale from turbulent velocity measurements at a single location. A model for the decay of horizontal coherence which accounts for the stability, roughness and instrument separation has been suggested in a previous paper by Panofsky and Mizuno. The present data compare favourably with this model. The effect of stability on coherence decay is found to have a definite site dependence. (A)