青藏高原大气水汽含量演变特征及其与夏季旱涝的关系

Atmospheric water vapor, an important atmospheric constituent, accounts for only a tiny part in the atmosphere, but it is the most actively component in the atmosphere and the major factor of cloud, precipitation and most of the weather events. Atmospheric water vapor which is directly related to many weather and natural disasters plays a major role in global climate change. Atmospheric water vapor is also the most abundant atmospheric greenhouse gas and makes the largest contribution to the radiation balance of the earth atmosphere system.. So it is of great significance to timely and accurate understanding of the Atmospheric water vapor content and water vapor changes..The distribution of the Atmospheric water vapor changes greatly as time and space. Inaccurate and discontinuous water vapor data is a major cause to the error of short-range weather forecast and influence the judgment of artificial precipitation enhancement conditions. Atmospheric water vapor content is the most difficult to measure accurately of all meteorological elements. Accurate atmospheric water vapor data is important for oceanic meteorology, hydrology, regional climate, aerospace and so on..The Tibetan Plateau, known as "China water tower or Asian water tower", is the core area of future water resources development and utilization in china. The water resources in the Plateau play an important role in the sustainable development of regional economy over the Tibetan Plateau and in China. Thus, understanding the atmospheric water resources status and its variation tendency has very important strategy sense. The drought conditions in an area have direct relation with the water vapor conditions in the region. The atmospheric water vapor content (i.e., precipitable water) indicates the precipitation that all the vapor in the whole atmosphere per unit area condenses and drops down to ground, one of the necessary conditions to become precipitation. Atmospheric moisture will directly influence the precipitation and it has closed relation with the precipitation range. The atmospheric water vapor is the important basis of water resources evaluation..With global warming, the shortage of water resources is an increasingly serious problem. In this study, based on the conventional observation data (radiosonde data and surface observation data), ground-based GPS data and various reanalysis data, calculate formula of atmospheric water vapor over the Plateau is obtained and the evolution characteristics of water vapor content over the Plateau are showed. Simultaneously key attention the relationship between the atmospheric water vapor and drought and flood in summer over the Plateau. By use in the diagnosis and simulation of the meteorological factors, probable mechanism of the precipitation conversion efficiency variation is put forward and it can provide an important reference for the water resources research and reasonable development of water resourc over the Tibetan Plateau.

水汽是地球大气的重要组成部分，其含量虽在大气中只占很小的一部分，但却是大气中最活跃的部分，水汽在大气中扮演着重要角色，是气候研究的重要参数，也是人工增雨的重要条件。水汽量是所有气象要素中最难精确测量的要素，准确的水汽资料对气象、水文等领域都有很重要的作用。青藏高原是我国未来水资源开发、利用的核心区，因此，了解高原空中水资源状况具有十分重要的战略意义。.本研究基于青藏高原常规探空站、地面站及地基GPS等观测资料，建立利用地面湿度参量表达的大气水汽含量经验表达式。在此基础上，全面揭示出本地区大气水汽含量的时空演变特征；同时结合地面降水资料，分析大气水汽含量的变化与高原夏季旱涝的关系，以降水转化率为切入点，对影响本地区降水转化率变化的各气象因子进行诊断和模拟，提出其变化的可能机理，从而为高原水资源研究及合理开发水资源提供重要的参考依据。

对青藏高原（以下简称高原）高空观测资料稀缺，本项目充分利用了中日JICA项目建立的高原地区地基GPS探测的逐时大气水汽含量（即大气可降水量，GPS-PWV）资料，以高原探空观测资料计算出的大气水汽含量（RS-PWV）为客观标准，分析了GPS-PWV误差的分布特征和原因；研究了高原夏季PWV的日变化和季节变化特征及其与地面降水的关系；揭示了高原夏季PWV的演变特征；建立了不同季节PWV与地面水汽压的经验拟合公式；诊断分析高原夏季旱涝年的降水转化率的异常。主要成果包括：高原各站PWV日变化主要以日循环为主和半日循环为辅；PWV存在明显的季节变化特征，呈现出明显的单峰型变化特征，同时表现出春季持续上升和秋季快速下降；近几十年来高原降水增幅普遍大于PWV的增幅；动力作用是影响降水转化率的主要原因之一，而降水转化率又是影响高原夏季旱涝的重要条件。本项目通过进行本地化后，提出GAMIT水汽解算方案对高原GPS水汽反演的精度有显著提高，研究结果表明高原GPS水汽资料具有优于探空观测的时空分辨率，该资料的应用将使高原水汽观测和研究水平的进一步提升；提出针对不同地区不同季节利用地面水汽压拟合PWV的经验公式，有助于充分挖掘地面观测信息；研究地面降水与PWV之间存在着复杂的日变化和季节变化关系，丰富了对高原夏季降水的认识和手段；提出了从降水转化率的角度分析夏季旱涝新思路，对于开展空中水资源有重要的借鉴意义。