Turbulent cascades in the Atmospheric Boundary Layers

Abstract

We investigate the scale-by-scale budget of the turbulence kinetic energy in the Atmospheric Boundary Layer (ABL) using airborne measurements performed by the helicopter-borne measurement system HELiPOD over the Baltic sea. The available, long time series of the turbulent wind velocity, temperature and humidity allow for a detailed study of turbulence properties in the ABL over the Baltic sea. In particular, we calculate the buoyancy forcing term and the third-order velocity structure function. The buoyancy’s production of turbulence energy is only significant at the largest-scales, above L = 100m. Unlike the ABL over the Atlantic in the shallow trade-wind regime, the buoyancy is dominated by temperature variations with little contribution from water-vapour mixing ratio. At the altitudes of the order of 100m studied here, a clear Kolmogorov equilibrium is observed at scales below 100m because of the combined absence of buoyancy and apparent presence of homogeneity and stationarity at these scales.