黄土高原夏季大气边界层发展结构及参数化对比研究

Loess Plateau locates in the Northernwest China. It is a typical semi-arid region, so the land-air interaction is especially strong in summer, which also caused a deep atmospheric boundary layer (ABL). Meanwhile, there are many different category of underlying surface within Loess Plateau, which caused the ABL there a kind of heterogeneous one. The specificity in the synoptic and climate process was noted for a long time. On one hand, the precipitation in some region of Loess Plateau is dominated by meso-scale to small-scale convective systems, which caused the rain there rather concentrated. Until now, the prediction of such kind of precipitation owns many problems by using numerical model. Especially, the choice of the parameterization of ABL is a crucial one. On the other hand, Loess Plateau is on the north of East Asia summer monsoon system, so the effect of ABL on the atmospheric circulation may spread to a larger scale. Based on the considerations above, this project mainly focuses on the ABL over loess Plateau on summer. The main content of research is arranged as follow. First, a field experiment will be applied in Pingliang city, which locates in the center area of Loess Plateau. A radiosonder is proposed to be released 3 hourly during the experiment period. Second, by taking use of numerical model, a series of simulation on the circulation near the experiment site will be compared with the observation to assess different parameterization schemes of ABL. Third, by choosing sever parameterization schemes who gives a better performance near the observation site, long term simulations will be applied on a larger region with Loess Plateau included. The differences in the climate signals, like the warming rate, among these simulations reflect the effect of ABL parameterization on the dynamic downscaling near Loess Plateau. Through the implementation of this project, a detailed structure of ABL over Loess Plateau is expected to be given, and the importance of ABL process and its parameterization scheme onto the numerical simulation of East Asia climate can be better understood.

黄土高原是我国西北典型的半干旱区域，当地夏季由于强烈的陆气作用而产生独特的气候特征。一方面，部分黄土高原地区，如平凉地区，夏季降水较为集中，盛行中小尺度的短时强对流降水。另一方面，黄土高原地理位置使得其陆气作用对于东亚夏季风环流也存在潜在影响。无论是局地降水特征，还是对区域气候的强迫，非绝热加热产生的深厚大气边界层（ABL）发展都在其中起着重要作用，因而ABL参数化方案的选择对当地天气气候模拟就非常关键。因此，本项目选择平凉塬区作为研究区域，进行如下研究。首先，在平凉地区进行近30天的连续探空观测，获得不同天气背景下的ABL连续发展数据。其次，利用数值模式比较不同ABL参数化方案在平凉地区的适用性。最后，选择几组较好的参数化方案对整个黄土高原进行长时间气候模拟，探讨ABL对于当地气候变化模拟的潜在影响。通过整个项目的执行，期望能对黄土高原夏季ABL的发展结构及其气候效应有更深刻的认识。

本项目以观测实验为基础，部分结合数值模式，对于典型黄土高原下垫面的陆气相互作用及大气边界层的一些经典问题进行了定量的分析。考虑到观测站点的分布，整个项目的研究区域大体分为两部分：以平凉站为代表的占据黄土高原主要面积的半干旱地区，和以黄河源为代表的高原湿润地区。对于半干旱地区，研究主要针对边界层参数化与黄土高原降水模拟展开。通过研究，初步对比了不同边界层参数化对于黄土高原气温和降水的影响；对于黄土高原的干旱与植被在气候尺度的变化关系进行了分析；对于陆气通量的涡动观测与大孔径闪烁仪的观测结果也进行了对比。在黄河源区域研究发现，暖季与冷季黄河源区的地表能量传输各自存在显著的独特性，体现在土壤表层水在不同形式的相变过程上；而从长时间看，黄河源南北部区域的蒸散呈现相反的趋势变化；黄河源区湖泊的CO2传输与湖陆温差存在显著关系，其年际变化主要受流量控制。整个项目资助发表科研论文16篇，其中SCI收录论文9篇，获批专利2项，培养毕业硕士研究生2名。从成果上看基本达到了项目预期目标，在一些关键问题上也取得了不错的进展。但从项目核心科学问题——黄土高原阵性降水与大气边界层发展的关系上来看，未取得具有决定性的结论。