Turbulent forcing of gravity waves during the morning transition of the Atmospheric Boundary Layer: analogy with water-tank experiments

摘要

In a series of atmospheric observations during the morning transition of the Atmospheric Boundary Layer (ABL), internal gravity waves were observed to propagate in the atmospheric Residual Layer. This requires an energy source for the waves and a stably stratified Residual Layer, which is usually though to be neutral. To understand these observations in a simplified and controlled environment, a series of laboratory experiments was carried out to examine the properties of internal gravity waves generated by a turbulent region and transmitted through a salt-stratified system similar to the atmospheric stratification during the transition. The turbulence was generated by an oscillating grid and analyzed using PIV technique to obtain the characteristic velocity U_t and lengthscale L_t of the energy containing eddies. The waves in the stratified layers were visualized using shadowgraph technique.