Effect of Large Eddy Vertical Resolution on Analysis of Entrainment and Tracer Vertical Transport Simulation
The effects of different scales of turbulent vortices in vertical direction on entrainment process and vertical transmission of tracers were studied, and the role of model vertical resolution in the analysis of simulation results was clarified by using field dense observation data in Dunhuang and large eddy model (LEM). The results showed that, in the vertical direction, the small-scale turbulence contributes more to the entrainment, and when small-scale turbulences are more, the clamping layer is even warmer. However, the thickness, strength and wind speed of the clamping layer are less affected by the scale of vertical direction turbulent vortices. Over the upper part of the entrainment layer, there are more updrafts and downdrafts with stronger intensities in the 50 m vertical resolution test. The distributions of vertical velocities, potential temperature and tracer concentration at different heights of the clamping layer are similar in the 10 m, 20 m and 30 m vertical resolution tests. In addition, the scales of vertical turbulent vortices affect the tracer vertical transport height slighty, but has a certain effect on the spatial distribution of tracer. When the large-scale turbulences are more and stronger, they are more favorable for the vertical transmissions of high-concentration tracers. Considering the noise generated in the simulation process and the longer computing time during the high resolution simulations, we use the 30 m grid spacing as LEM vertical resolution in simulating, which is an ideal choice. In such a case, the model can simulate not only the average structure of the entrainment layer, but also the very fine turbulence distribution in the clamping layer.