稀疏植被下垫面与大气相互作用研究进展

Review of Study on Interaction between Underlying Surface with Sparse Vegetation and Atmosphere

介绍了国家自然科学基金委员会"十五"重点项目"稀疏植被下垫面与大气相互作用研究"的成果。通过资料分析、数值试验和理论分析,研究干旱地区稀疏植被复杂下垫面上水、热及CO2输运过程的机理;非均匀下垫面的复杂非线性效应;干旱地区更合理的陆面过程参数化方案以及绿洲的稳定性;强沙尘暴的发展机制和干旱地区生态环境建设对策。主要结果表明:(1)揭示了植物生态生理过程、净第一生产力和生物量对气候的敏感性,为稀疏植被下垫面与大气相互作用研究提供了较好的接口。(2)发展了适用于干旱、半干旱地区土壤中水热输送交叉耦合的物理模型;以能量和物质守恒定律为基础的雪盖物理模型,它显著地改善了陆面过程的模拟效果,是国际上最早开发的同类模型之一。(3)发展了大气非平衡态热力学,证明了非线性区普遍成立的最小熵产生原理,为研究气候和环境复杂系统提供了新思路和新方法;揭示了大气辐散和辐合运动对垂直湍流输送的影响,非均匀下垫面地气相互作用,为非均匀下垫面陆面过程参数化提供了物理基础;研究了绿洲稳定性并估算了绿洲临界尺度约为3～6km,为绿洲保护和建设提供了理论依据;提出了干旱地区有限水资源条件下增强其稳定性和抗干扰能力的生态环境建设对策。(4)发展了强沙尘暴发展的动力学模式。

The studies of a key project, entitled \!study of interaction between underlying surface with sparse vegetation and atmosphere\' supported by National Natural Science Foundation of China from 1999 to 2003 are reviewed. The mechanisms of transport processes of water, heat, and CO_(2) over complex underlying surface with sparse vegetation, the complex nonlinear effects caused by the heterogeneous underlying surface, the oasis stability, the development and thermal-dynamic conditions of strong dust storm, the countermeasure building the ecological environment in the arid and semi-arid area are studied using the data analyses, the numerical experiment, and the theory analyses. The main results are as follows: (1)Revealing the sensitivity of the net first productive power and the biomass to the climate, especially to the mean annual precipitation. These can provide a better interface to future study the interaction between the underlying surface with sparse vegetation and the atmosphere. (2)Developing a physic former, which expresses across coupling between the water transportation and the heat transportation in the soil, and the influence of phase transition on movements of water and heat in the soil, to be applicable to the arid and semi-arid area. A physic former that express variation of the seasonal snow cover based on the conversation law of energy and the conservation law of mass is developed, its simulated results are very good consistent with the observation results, which is one among several international typical delaminating formers of snow cover to achieve in-phase with international advanced level. (3)Developing the nonequilibrium thermodynamics. A theorem of minimum entropy production and a theorem of minimum generalized energy of the force-dissipative dynamic system are proved in thermodynamic linear and nonlinear region. These theory advances offer potential new idea and new method to deal with the kind of complex climate and environment system. The nonequilibrium linear thermodynamics reveals that the atmospheric vertical movement (namely the horizontal convergence or divergence movement) influences on the vertical turbulent transport fluxes of maroscopic quantities. This is very important for the boundary layer of heterogeneous underlying surface and the convection boundary layer. This research provides important clue to overcome difficulties in application of the atmospheric boundary layer physics to heterogeneous underlying surface, and in the parameterization of land surface process of heterogeneous underlying surface. Theoasis microclimate, the oasis critical scale and the oasis stability are studied using the theory of nonlinear thermodynamics. The oasis physic scale and the oasis wet island intensity are important control parameters of thermodynamic and dynamic processes of the oasis. The results of numerical simulation of the atmospheric dynamic model show that the critical scale of forming the oasis cold island effect is about 3～6 km; The oasis wet island intensity is about 2～5 g·kg^(-1). On the basis of the above research stockpile, we suggest countermeasure of protecting and building the ecological environment in arid area. (4)The development mechanism of strong dust storm, the atmospheric dynamic condition and the surface thermodynamic condition of forming strong dust storm are studied, on the basis of demand of economy build, and on the basis of trend of continually increasing of the dust storm in Western China and Northern China in the recent years. These simulated and observed results unveil a positive feedback process of the radiation cooling, among the dust, the radiation, the air temperature, air pressure, and strong wind, in the dust storm development process. These theoretical results validate the physic mechanism of forming the dust storm, and reveal good foreground of predicting the strong dust storm.