An investigation for influence of intense thermal convection events on wall turbulence in the near-neutral atmospheric surface layer

Abstract

Based on the field observation data in the near-neutral atmospheric surface layer (ASL) at the Qingtu Lake Observation Array, a new experimental data processing of the second-order statistic distribution of the high Reynolds number wall turbulence was presented which considered the influence of the intense thermal convection events (ITCEs). Following the conventional data selection in the literature, i.e., |z/L|, it is known that the variation of the large- and/or the very-large-scale motions (LSMs and VLSMs) cannot be effectively performed only by this method, which motivates us to find other factors influencing these turbulent motions, e.g., the ITCEs. From the data analysis of the probability density distribution of vertical heat flux, it is found that although its mean value tends to zero, its variance is large rather than zero, which suggests to us some ITCEs exist in the natural motions, although it has less frequent occurrences. In order to characterize the effect of such ITCEs, an additional parameter ψ for scaling the ratio of the buoyancy force to the viscous force is proposed in the data selection progress. The results show that the greater the |ψ|, the greater the impact of the ITCEs on ASL wall turbulence. Furthermore, our investigation reveals that the ITCEs may be one of the reasons why the VLSMs exhibit the Top-Down mechanism.