A clustering method to characterize intermittent bursts of turbulence and interaction with submeso motions in the stable boundary layer

Abstract

Atmospheric boundary layers with stable stratification include a variety of small-scale non-turbulent motions such as waves, microfronts and other complex structures. When the thermal stratification becomes strong, the presence of such motions could affect the turbulent mixing to a large extent and common similarity theory that is used to describe weakly stable conditions may become unreliable. We apply a statistical clustering methodology based on a bounded variation, finite element method (FEM-BV) to characterize the interaction between small-scale non-turbulent motions and turbulence. The clustering methodology achieves a multiscale representation of nonstationary turbulence data by approximating them through an optimal sequence of locally stationary multivariate autoregressive factor models (VARX) processes and some slow hidden process switching between them. The clustering method is used to separate periods with different influence of the non-turbulent motions on the vertical velocity fluctuations. The methodology can be used in a later stage to derive a stochastic parameterization for the interactions between non-turbulent and turbulent motions.