Study on a boundary-layer numerical model with inclusion of heterogeneous multi-layer vegetation

On the basis of improving the algorithm of the mixing length in and above f orest canopies, a PBL numerical model including the multi-layer, heterogene ous vegetation is developed. Simulations indicate that different treatments of mixing length can make a great difference in the wind field especially for dense forest, and results from the improved mixing length scheme are in better agreement with observations than those from the original scheme. It may be expected that the improved mixing length scheme can lead to more ra tional turbulent transfer than the original one. From the sensitivity exper iments, we obtain the characteristics of both wind and temperature profiles in and above plant canopies, e.g., during the daytime, a stable thermal st ratification exists near the surface in the canopies, but a neutral or slig htly unstable condition appears above plant canopies, while at night the re verse situations occur; the increase of the temperature of the dense-forest case is less than that of the sparse-forest case; the windspeed is reduced within the canopy layer and the large wind shear occurs near the treetop, etc.