边界层参数化方案对边界层热力和动力结构特征影响的比较

本文利用高分辨率中尺度WRF模式，通过改变边界层参数化方案进行多组试验，评估该模式对美国北部森林地区边界层结构的模拟能力，同时比较了五种不同边界层参数化方案模拟得出的边界层热力和动力结构.结果表明：除个别方案外，配合不同边界层方案的WRF模式都能成功模拟出白天对流边界层强湍流混合特征和夜间稳定边界层内强逆温、逆湿和低空急流等热力和动力结构.非局地YSU、ACM2方案在白天表现出强的湍流混合和卷夹，相比于局地MYJ、UW方案，模拟的对流边界层温度更高、湿度更低、混合层高度更高、感热通量更大，更接近实际观测，这表明在不稳定层结下考虑非局地大涡输送更为合理，但局地方案在风速和风向的预报上存在一定优势.TEMF方案得到的白天局地湍流混合强度为所有方案中最弱，混合层难以发展，无法体现对流边界层内气象要素垂直分布均匀的特点.对于夜间稳定边界层的模拟，不同参数化方案之间的差异较小，但是YSU方案在一定程度上高估了机械湍流，导致局地湍流混合偏强，从而影响了其对稳定边界层的模拟能力.

Comparison of the thermal and dynamic structural characteristics in boundary layer with different boundary layer parameterizations

To evaluate model performance of simulating structural characteristics in boundary layer at the forested areas of northern United States and compare the thermal and dynamic structural characteristics in boundary layer with five different boundary layer parameterizations, high resolution mesoscale WRF model was used in this paper to conduct some experiments with different boundary layer parameterization configurations. The results showed that WRF model with different boundary layer schemes could successfully simulate the characteristics of strong turbulent mixing in boundary layer at daytime and strong inversion, inverse wet and low level jet in stable boundary layer at nighttime except for some individual schemes. Compared with local schemes MYJ and UW, the nonlocal schemes YSU and ACM2 simulated strong turbulent mixing and entrainment at daytime, producing higher temperature, lower humidity, higher mixing layer, larger sensible heat flux in convective boundary layer, which were closer to the results of observations. This indicated that considering the nonlocal transport of large eddy was more reasonable in the instable stratification. But local schemes had some advantages in the prediction of wind speed and direction. TEMF scheme predicted the weakest local turbulent mixing in all schemes, which was difficult to form the mixing layer, and could not describe the characteristics of vertically homogeneous distribution of meteorological elements in convective boundary layer. For nocturnal stable boundary layer simulation, the discrepancies from different schemes were small. But to a certain extent, the scheme YSU overestimated mechanical turbulence at nighttime, leading to strong local turbulent mixing, and could not simulate stable boundary layer well.