High-resolution large-eddy simulations of stably stratified flows: application to subkilometer-scale turbulence in the upper troposphere–lower stratosphere

Abstract

Large-eddy simulations of stably stratified flows are carried out and analyzed using the mesoscale atmospheric model Méso-NH for applications to kilometer- and subkilometer-scale turbulence in the in the upper troposphere–lower stratosphere. Different levels of turbulence are generated using a large-scale stochastic forcing technique that was especially devised to treat atmospheric stratified flows. The study focuses on the analysis of turbulence statistics, including mean quantities and energy spectra, as well as on a detailed description of flow topology. The impact of resolution is also discussed by decreasing the grid spacing to 2 m and increasing the number of grid points to 8 × 109. Because of atmospheric stratification, turbulence is substantially anisotropic, and large elongated structures form in the horizontal directions, in accordance with theoretical analysis and spectral, direct numerical simulations of stably stratified flows. It is also found that the inertial range of horizontal kinetic energy spectrum, generally observed at scales larger than a few kilometers, is prolonged into the subkilometric range, down to the Ozmidov scales that obey isotropic Kolmogorov turbulence. This study shows the capability of atmospheric models like Méso-NH to represent the turbulence at subkilometer scales.