Modulation of the atmospheric turbulence coherent structures by mesoscale motions

Abstract

The precise modeling of turbulence is indispensable for weather forecasting and environmental heat-removal and pollution-dispersion assessment. Models rely on correlations derived from field measurements. Unfortunately, the readings are usually contaminated with mesoscale motions which alter turbulence statistics and mislead the characterization of turbulence coherent structures, the drivers of the heat and mass transport process. This article depicts the interference of the mesoscales in turbulence statistics and coherent structure detection. Atmospheric measurements were taken at EKOMAR on the east coast of Malaysia. Two ultrasonic anemometers at heights of 1.7 and 12 m were utilized. Twelve samples from the convective atmospheric boundary layer were analyzed. Spectral and auto-correlation analysis were conducted to assess the weight of the mesoscales relative to the shear coherent structure scales. The structure inclination angle and timescale were calculated for the wind speed signal with and without the mesoscale scales filtered out. It was found that these interfering structures largely shifts the calculated length- and time-scales of the coherent structures. The improper filtration of the signal may delete part of the coherent structures and hence worsen the situation.