Helicity and Turbulence in the Atmospheric Boundary Layer

Abstract

Helicity is inherent in many circulating motions and structures in the atmospheric boundary layer (ABL), where it is continuously reproduced due to the combined action of the Earth’s rotation and friction, which also is closely related to the phenomena of the inverse cascade and large-scale restructuring of flows. The helicity factor should be correctly considered during the construction of atmosphere models, and, accordingly, the knowledge of the helicity distribution in the ABL and its relation to dynamic atmospheric processes is required. In this study, the helicity of the circulation structures of various spatial and temporal scales in the ABL is determined from an analysis of field measurement data. A qualitative and quantitative comparison with the observed values is carried out on the basis of results of numerical simulations using the quasi-two-dimensional model and a WRF-ARW mesoscale atmospheric nonhydrostatic model, in particular, WRF-LES. A good agreement with the observed spatial distributions of circulating motions is obtained. A link between the turbulent characteristics and helicity of the structures under study is shown. The helicity estimates for circulation structures of various scales in the ABL and in the free atmosphere are compared.