Advances on the Links Between Turbulent and Submeso- to Mesoscales During EUREC4A

Abstract

Turbulent processes in the atmospheric boundary layer (ABL) are parameterized in numerical weather prediction and climate models. Better understanding their modulation by larger-scale organized structures, some of them being represented explicitly, is thus of great interest. In this study, we test an innovative statistical tool, the Wavelet Scattering Transform (WST) on turbulent measurements of 3D velocities at different levels in the ABL during the ${\text{EUREC}}^4$A campaign near Barbados. The measurements were done in trade wind environment over the sea. They encompass two categories of ABL convection, roll vortices (RV) or convective cells (CC) whose organization depends on cold pool and density currents. Statistical tools such as Fourier transforms or moment analysis give access to levels of energy, characteristic sizes and variances in CC and RV conditions. The WST provides further information, with strong modulations of the turbulent scales by submeso- to mesoscales in CC, whereas modulating scales are smaller than the horizontal scale of rolls in RV. Penetrating dry tongues from the ABL top are revealed by modulation scales varying with height. In RV conditions, modulations differ in cross-wind and along-wind observations confirming that along-wind measurements do not provide good sampling of the ABL turbulence. WST are a valuable tool for investigating ABL turbulence and its interactions with coherent structures, and could be used on scalar variables and surface fluxes.