Interaction of submeso motions and intermittent turbulence in a very stable boundary layer

Turbulence structure in the very stable boundary layer (SBL) is characterized by complex interactions between the static stability of the air and non-turbulent processes that govern the mechanical generation of turbulence. Submeso motions, on scales from meters to few kilometres, can perturb the turbulence structure and can modulate the turbulent fluxes through the production of intermittent mixing events related to localized flow acceleration. Submeso motions can take a variety of forms including gravity waves, density currents, drainage flows. An important fraction of them is represented by horizontal meandering modes, particularly when the large-scale flow is weak. However, their characteristics and their impact on turbulent transport are yet poorly studied and understood. This talk aims to provide some insight into the characteristics of different submeso motions and on their role in the intermittent turbulence productions in a very SBL. Analyses of micrometeorological data characterised by different surface conditions and SBL structure are presented. Data were collected at micrometeorological towers placed in an Antarctic Ice sheet (Terra Nova Bay - Antarctica), a forested canopy (Duke Forest, NC - USA) and a coastal site (Linhares - Espirito Santo State). Experimental data have been analysed using different methodologies, such as the Eulerian auto-correlation functions, the wavelet analysis, and the multi-resolution flux decomposition. The combination of these approaches enables i) the identification of periods interested by horizontal and vertical submeso motions, ii) the investigation of the mechanism of turbulence generation by submeso motions on different time-scales and iii) their role in influencing the turbulent transport in very stable low-wind conditions.