Impact of nocturnal low-level jets on surface turbulence and fluxes

Abstract

The effect of low-level jets (LLJs) on surface turbulence and fluxes in the nocturnal stable boundary layer is investigated by using extensive sodar and tower observations from two experimental sites in the United States. Surface turbulence and fluxes are found to be typically stronger and more structured during LLJs, not corroborating the shear-sheltering theory. Results from a turbulence kinetic energy budget analysis indicate a reasonable contribution by the pressure transport term during LLJs, possibly related to an interaction between LLJs, gravity waves, and turbulence. Turbulence statistics are found to follow Monin-Obukhov similarity/z-less theory very well during LLJs, in general. Under very stable conditions, however, the results indicate a departure from local similarity, possibly associated with the input of non-local turbulence via pressure transport. The findings are of relevance for observational and modeling studies of the nocturnal stable boundary layer, including studies of surface-atmosphere exchange and pollutant dispersion.