Intermittency in the atmospheric surface layer: Unresolved or slowly varying?

Abstract

We present streamwise velocity structure functions 〈 δ v L ( τ ) 〉 = 〈 | v ( t + τ ) − v ( t ) | p 〉 (with p = 1 : 5 ) obtained in the near neutral atmospheric surface layer at the Utah SLTEST site at the highest terrestrial Reynolds number R e τ = O ( 10 6 ) . We show that the occurrence of very large scale coherent oscillations in the streamwise velocity throughout the wall region, interpreted as genuine structural features of the canonical turbulent boundary layer, affects the scaling exponents of the p > 3 order structure functions. This results in a slight alteration of the intermittent behavior of the velocity field. It was found that for positive (fast) large scale oscillation of the low-pass filtered velocity signal, deviations from the Kolmogorov K41 prediction (absence of multiscaling) are more marked, as compared to negative (slow) excursion. The results are discussed in terms of convergence of statistics from atmospheric boundary layer measurements.