基于观测试验的塔克拉玛干沙漠腹地陆面过程参数化方案的发展及模拟

Taklimakan Desert is the second largest shifting sand desert in the world, also one of the main origin of the global dust storms, with severe natural environment and extremely arid climate, and wide range of shifting sand dunes with various types. Therefore, it has an important influence on regional and global climate and atmospheric circulation. Thus, it becomes the ideal regions to research for special land-surface process. This project will take the Tazhong Station for Desert Atmospheric Environment Observation and Experiment as an experimental base, using high-precision observational instruments and advanced experimental methodologies, based on existing observations, carrying out a series of targeted intensive observation experiment to land-surface process. Thereby, in order to quantitatively analyze the vertical structure of momentum and heat as well as turbulent fluxes on near-surface layer, the methods of the theoretical research, numerical analysis, parametric experiments, land-surface process models' simulation and so on will be adopted. And then, we are going to analyze the relationships of the momentum, heat, moisture and radiation exchange between the land-surface and atmosphere, to study the characteristic parameters of land-surface process, land-surface energy balance characteristics and its evolution in desert regions, and to develop and improve the parameterization schemes of land-surface process so as to suitable for desert regions. Meanwhile, these revised parameterization schemes will be applied to some typical land-surface process models (e.g. SiB2, CoLM and CLM), so our aim is to improve their abilities to simulate on the desert areas. Subsequently, the variation characteristics of fluxes near the ground will be analyzed through the comparing experiments between simulations and observations, by which to increase the knowledge and understanding of the rules of land-atmosphere interaction to the extremely climatic region-Taklimakan Desert.

塔克拉玛干沙漠是世界第二大流动沙漠，自然环境严酷，气候极端干旱，是全球沙尘暴的主要起源地之一，流沙范围广，沙丘类型多样，与全球其他区域对比强烈，对区域和全球气候及大气环流有着重要的影响，是特殊陆面过程研究的理想靶区。本项目以塔中沙漠大气环境观测试验站为基地，采用高精度的观测仪器和先进的试验手段，在已有观测试验的基础上，有针对性地进行陆面过程强化观测试验，利用理论研究、数值分析、参数化试验和陆面过程模拟等方法，定量地解析近地面层的热力和动力的垂直结构和湍流通量，地气间的动量、热量、水分和辐射的交换关系，研究沙漠腹地的陆面过程特征参数以及地表能量平衡特征和演变规律，发展和改进符合沙漠地区的陆面过程参数化方案。并将这些参数化方案应用到多个典型的陆面过程模式中，以期改善陆面过程对沙漠地区的模拟能力。再通过模拟与观测的对比试验，分析近地层通量的变化特征，加深对该极端气候区地气相互作用规律的认识。

塔克拉玛干沙漠是特殊陆面过程研究的理想靶区。本项目以塔中沙漠大气环境观测试验站为基地，在已有观测试验的基础上，有针对性地开展陆面过程强化观测试验。定量解析地气间的动量、热量、辐射的交换关系，研究并确定了沙漠腹地的陆面过程特征参数，发展和改进了适合沙漠地区的陆面过程参数化方案。选择通用陆面模型CoLM，开展了参数化方案模拟试验研究，改善了陆面过程对沙漠地区的模拟能力。. 本项目的研究主要获得以下结果：建立了高质量的长时间周期的沙漠腹地陆面过程观测数据库。建立了一套完整的塔克拉玛干沙漠地表宽波段地表比辐射率光谱库。对沙漠腹地的Monin-Obukhov相似函数进行了修正，为提高计算湍流通量、地表粗糙度和总体输送系数的精度奠定了基础。研究了沙漠腹地地表粗糙度日、月变化特征，动力学粗糙度变化很小，获得了最佳长度值；而热力学粗糙度的日、月变化明显，找出了适合沙漠地区的参数化方案。研究了沙漠腹地地表整体输送系数，获得了不同大气稳定度下的平均值。得到了沙漠腹地地表反照率的参数化方程，而不再采用一个定值，这能够真实反映辐射平衡。详细观测了整个沙漠地区的地表比辐射率光谱特征，得到了精确的比辐射率值，结合MODIS卫星数据，得到了计算塔克拉玛干沙漠地表比辐射率的方程，并且获得了整个沙漠地区的比辐射率分布特征。对比分析了几种土壤热扩散率的计算方法，获得了精度最高的计算方法。经过参数值的校正与参数化方案的修正，开展了陆面过程模拟试验，改善和提高了陆面模式CoLM在沙漠地区对感热通量、地表热通量、地表和土壤温度模拟的精度。. 改进的陆面过程参数化方案模块已经尝试在WRF气候模型中使用，发现能够改善目前已有的气候模型在预报新疆塔里木盆地气温时，出现高估沙漠气温而低估周边绿洲气温的缺陷。因此，中国气象局乌鲁木齐沙漠气象研究所正在尝试改进和完善气候模式，将这一成果应用到新疆的气象预报模式中。