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.