青藏高原地区对流云系及其对能量和水循环的影响研究

The important roles of the Tibetan Plateau played in establishing and maintaining the Asian summer monsoon circulation have been pointed out by many previous studies. The observational, laboratory,numerical experiments, and theoretical works have investigated extensively the orographic and thermal effects of the Tibetan Plateau on the large-scale summer circulation over Asia. The seasonal variation of the heating of the Plateau results in the reversal of the meridional temperature gradient and the change of the general circulation over East Asia. Various mechanisms have been proposed to explain the heat sources estimated by the month-long heat and moisture budgets over the Tibetan Plateau and surrounding regions. However, due to the limited observations, there is lacking of studies on the structure and characteristics of cloud systems over the Plateau. In this project, we propose to attack this long-standing problem by combining the observational analysis and numerical modeling. We will conduct the heat and moisture budgets using the NCEP and ECMWF reanalysis data and use the objective analysis to include the measurements from the special Tibetan Plateau experiments. The large-scale forcing data from the analysis will be used to force the high-resolution numerical model, i.e., the cloud-resolving model (CRM), for months-long simulations of convection and clouds during summer (May-July). The evolution and vertical distribution of cloud systems will be examined with the model-simulated cloud-scale properties. The contribution of cloud microphysical processes to the convective heating will be examined with the model outputs. The effects of cloud systems on the radiation budgets in the top of the atmosphere and the surface, the hydrological cycle, as well as the heating mechanisms will be investigated and compared between the regions over the Tibetan Plateau and the surrounding areas. The successful completion of this project will not only further our understanding of cloud systems over the Tibetan Plateau, but also provide unique cloud-scale properties for evaluating and improving the convection parameterization scheme, and consequently, an improved general circulation model (GCM) simulation of the Asia summer monsoon.

大量研究证实青藏高原对亚洲季风形成与维持有重要作用。对青藏高原动力和热力作用及其对亚洲季风环流的影响进行了广泛研究，包括理论、观测和数值模拟等。青藏高原热力的季节变化致使南部温度梯度转变以及东亚环流变化，已有多种机制来解释季节转换期间高原的热源特征。然而，由于缺乏观测资料，对青藏高原云系垂直结构和演变特征的研究较少。本项目将综合利用观测资料和数值模拟来研究该问题。使用再分析数据结合最新观测，特别是把青藏高原的观测数据进行客观分析，来推导高原地区的热量和水汽收支； 由得到的大尺度强迫场驱动云分辨模式进行数值试验；利用模式输出的云尺度特性检验云系演变、垂直结构和微物理过程对加热的贡献；通过与周围地区对比，研究高原云系对辐射收支、水循环和加热机制的影响。这不仅能促进对青藏高原云系结构和演变特征的系统认识，又能提供丰富的云参数，有助于评估和改进积云对流参数化方案，提高大气环流模式对东亚季风的模拟。

大量研究证实青藏高原对亚洲季风形成与维持有重要作用。对青藏高原动力和热力作用及其对亚洲季风环流的影响进行了广泛研究，包括理论、观测和数值模拟等。青藏高原热力的季节变化致使南部温度梯度转变以及东亚环流变化，已有多种机制来解释季节转换期间高原的热源特征。然而，由于缺乏观测资料，对青藏高原云系垂直结构和演变特征的研究较少。本项目综合利用已有的观测资料、再分析数据以及多种卫星数据综合、系统的研究了高原云降水过程。使用再分析数据计算了青藏高原地区大气热源和水汽汇，并将它们与云降水过程相联系，揭示了高原东、西部不同类型云系对局地热源和降水的贡献特点；通过高原和下游地区的深对流系统进行统计分析，发现高原东部的深对流强度和频率与长江中下游地区的深对流系统呈现出正相关关系，该结果使得高原对下游水汽输送的理论有了云降水活动的支持；使用计算得到的大尺度强迫场驱动云分辨模式进行数值试验，得到了高原夏季为期一个月的云降水活动信息，揭示了高原夏季对流系统具有云体浅薄、降水能力弱、生命史较短的特点，并且不会出现平原地区那样极强的对流系统；利用敏感性试验发现高原的典型降水事件是较强的地表热力通量和合适大尺度环流场共同作用的结果，并且高原西部的强降水过程依赖于外来水汽输送；揭示了高原地表热力通量和大尺度环流对高原云降水日变化的影响。项目已发表高水平学术论文7篇，期中SCI论文6篇，EI论文1篇。培养博士3名，硕士3名，圆满甚至超额完成了项目计划任务书的研究内容，达到了预期目标。