Persistence of velocity fluctuations in non-Gaussian turbulence within and above plant canopies

This study focuses on the distribution of time scales and its relation to integral time scales in non-Gaussian turbulence within plant canopies. We introduce the idea of persistence usually used to describe nonequilibrium systems to the analysis of time series of turbulence as a simple approach to characterize the distribution of time scales. Analysis of turbulence data within and above a cornfield shows that the integral time scale is not adequate to characterize the duration of long events in non-Gaussian turbulence. Positive and negative events have different time scales as a consequence of the skewness of the velocity fluctuations. Sweeps (u' > 0 and w' < 0) are stronger and have shorter durations, and dominate the behavior of the integral time scale. At the same time, ejections (u' < 0 and w' > 0) tend to be much longer lived, and their signature (which is not clearly seen in the integral time scale) is clearly identified in the distributions of persistence time. (C) 2013 AIP Publishing LLC.