【作者】 李国平；

【导师】 黄丁发；

【作者基本信息】 西南交通大学 ， 大地测量学与测量工程， 2007， 博士

【摘要】 常规大气水汽探测手段的时空分辨率极大地制约了人们对水汽时间变化和空间分布的认识，使我们对局地和全球水汽分布和水份循环缺乏详尽的了解，水汽信息的欠缺影响了灾害性天气预报特别是暴雨短时临近预报的水平，也限制了数值天气预报中降水量预报的精度。因此，水汽是大气中人们了解和认识得不够充分的大气成分之一，如何用新的技术手段精确测量大气水汽含量，是当今气象学所面临的一项重要任务。作为GPS大地测量学的反演问题，GPS技术为探测大气水汽提供了一种全新的手段，它具有实时、连续、不受天气状况影响、精度高、成本低等优点，是传统大气水汽观测手段的有力补充。本论文从GPS遥感水汽的理论及气象学应用的角度，全面分析了GPS反演水汽技术在气象中的应用领域，研讨了地基GPS技术反演大气可降水量的计算方案及主要步骤，讨论了GPS遥感大气水汽的主要误差源。本论文的研究内容主要分为以下四个部分：(1)研究无线电探空气象资料计算大气可降水量的方法、误差及其改进。应用探空气象资料分析并评估地基GPS遥感大气可降水量技术的精度。评估了对流层水汽加权平均温度的计算公式在成都和华北地区的适用性及其改进方案，特别讨论了估算加权平均温度的几种方法及其对高精度反演可降水量的影响。根据成都和华北地区的气象探空资料，采用数值积分法，计算出相应时刻的对流层加权平均温度，分析了成都和华北地区应用Bevis经验公式计算加权平均温度的适用性及其所产生的误差。通过线性回归分析得到成都和华北地区利用地面气温等气象参数计算加权平均温度的拟合公式，初步探索了Bevis公式的局地修正方案。研究表明，反演大气可降水量所用到的加权平均温度及其拟合公式具有明显的地域和时间特征。因此在地基GPS气象研究和业务试验中，应该利用当地长期气象资料建立适宜的加权平均温度的计算模型，这对于提高GPS反演大气水汽可降水量的精度具有重要作用。(2)根据成都和华北地区无线电探空资料，计算出地面水汽压与大气柱中的可降水量，并分析了两者之间的关系，结果表明大气可降水量与地面水汽压存在较好的数值对应关系。由此为在缺乏气象探空资料或GPS遥感水汽缺测的情况下，利用地面水汽压估算大气可降水量提供了一种简便易行的替补方法，拟合出的经验关系式在大气水汽研究与应用工作中具有较大的实用价值。(3)进行成都地区利用地基GPS观测网遥感区域大气可降水量的首次试验。利用首个成都地区地基GPS观测网2004年7～9月的测量数据，通过Bernese GPS Software V4.2解算出天顶总延迟量，结合自动气象站获得的气象资料计算出GPS遥感的大气可降水量。与根据气象探空站资料算出的可降水量进行了统计对比，确定出本次GPS遥感可降水量试验的精度为3.09mm，两种可降水量时间序列呈现高度的一致性。同时验证了计算对流层加权平均温度的Bevis回归公式在成都地区的适用性。试验结果确认了在成都地区应用GPS技术探测大气可降水量的可行性，为多学科综合研究大气水汽的时空变化以及在短时临近天气预报、空中水资源开发、人工影响天气等多方面的应用奠定了基础。(4)研究了不同地形作用下、不同气候区中GPS大气可降水量的时间变化及空间差异，分析了大气可降水量与气压、气温、水汽压和降雨量等地面气象要素以及降雨天气过程的关系。重点研究了GPS遥感的可降水量的日循环特征以及与局地环流、局地降水特点的联系。以日本中部地区作为第一试验区，利用GPS遥感的大气可降水量资料和地面气象资料研究了海洋性季风气候下大气可降水量的日变化特征，并将其变化特征归纳为山区、盆地和平原-海岸三类。研究表明，日本中部大气可降水量具有明显的日循环特征，白天大气可降水量变幅的最大值出现在盆地，最小值出现在平原。测站周围地形产生的局地热力环流对大气可降水量的日变化有显著影响。大气可降水量日变化最明显的特征就是最大值出现在夜间，而降水峰值出现在午后或夜间，夜雨频率很高，这说明实际降水量和大气可降水量的日变化存在很好的关联。以成都平原作为第二试验区，利用首个成都地区地基GPS观测网解算出的大气可降水量数据，对青藏高原大地形下盆地气候区中的成都、郫县夏季可降水量的日循环特征进行了合成分析。结果表明：可降水量同样呈现明显的日循环特征，最小值出现在早上，最大值出现在下午。白天可降水量的变化较大，夜间相对稳定。降水日变化的一个显著特点是降水主要发生在夜间，当可降水量在下午达到最大之后，主降水阶段开始；当可降水量下降到一个稳定状态后，主降水过程随之结束。可降水量的积累和释放与地面降水有较好的对应关系，可降水量的持续性递增和持续性递减分别预示着降水的开始和结束。最后还利用成都和华北地区地基GPS遥感的可降水量和自动气象站测得的实际降水量资料，对几次暴雨天气过程中GPS可降水量的演变特征进行了初步分析，其结果有助于归纳出GPS可降水量用于各种降水天气的预报指标，尤其对暴雨天气的短时临近预报具有重要的参考价值。更多还原

【Abstract】 The resolution of conventional observation for atmospheric water vapor extremely restricts the level of our understanding for the spatial and temporal distribution of water vapor, thus the detailed knowledge of local and global distribution of water vapor and cycle of water vapor is poor. The lack information of water vapor affects the level of forecast of severe weather especially for the nowcasting of heavy rainfall, and limits the accuracy of numerical prediction about amount of rainfall. Thus the water vapor is one of atmospheric composition we have to know more. It is an urgent task for meteorology today that atmospheric water content should be measured more accurately by a new technology.As an inverse problem of GPS (Global Positioning System) geodesy, the technology of detecting atmospheric water vapor based on GPS provides a new means for remote sensing atmosphere with many advantages such as real-time, continuity, high precision, low cost and unaffected by weather, which has become a powerful supplementation for routine atmospheric sounding system. In the view of the theories of remote sensing water vapor based on GPS and applications in meteorology, the applied fields of GPS technology in meteorology are analyzed comprehensively, the computational scheme and basic steps are studied, and main error resources in the computation of atmospheric water vapor by using ground-based GPS data are discussed in this thesis.The main contents of this thesis include following four parts:(1) The method, error analysis and improvement in the computation of atmospheric water vapor are studied. The accuracy of estimating atmospheric precipitable water vapor by ground-based GPS is evaluated by using radiosonde meteorological data. The suitability and improvement of the formula for calculating the mean weighted tropospheric temperature in Chengdu and North China are discussed; some methods of estimating mean weighted temperature and their influences on high precise precipitable water vapor derived from GPS are compared.The sequence of mean weighted temperature using integral method is obtained using the data of radiosonde in Chengdu and North China, and the suitability and error of Bevis’s regression formula to estimate mean weighted temperature using surface air temperature are analyzed. The linear regression formulas of estimating mean weighted temperature in different types are established, and some modified Bevis’s formulas available in Chengdu and North China are suggested. There is difference of Bevis’s formula in different months and different areas, thus for high precise precipitable water vapor derived from ground-based GPS, it is very important for ground-based GPS meteorology to determinate local regression formula for estimating mean weighted temperature based on the long-term radiosonde data.(2) According to the meteorological sounding data from the radiosonde stations in Chengdu and North China, the precipitable water vapor and surface water-vapor pressure are computed and the relationships between these two factors are analyzed. The results indicate that the relationship between precipitable water vapor and the corresponding ground water is highly linear. From this, it is possible to calculate the precipitable water content of the entire atmosphere only by using the ground water, which can be as a simple spare method under the condition of no radiasonde data or GPS data. Therefore, this replacement and related empirical formulas have good actual values in the research and application of atmospheric water. (3) The first experiment of remote sensing local precipitable water vapor by using ground-based GPS network in Chengdu area has been finished. The estimates of total zenith delay are available using Bernese GPS Software V4.2 based on GPS data every 30 second from the first measurement experiment of a ground-based GPS network in Chengdu Plain of southwest China during the period of July to September 2004. Then estimates of 0.5 hourly precipitable water vapor derived from GPS are obtained using meteorological data from automatic weather stations. The comparison of precipitable water vapor derived from GPS and those from radiosonde observations is given at Chengdu station, with RMS (Root Mean Square) differences of 3.09 mm. The consistency of precipitable water vapor derived from GPS to those from radiosonde is very good. It is concluded that Bevis empirical formula for estimating the weighted atmospheric mean temperature can be basically applicable in Chengdu areas because the relationship of GPS PWV with Bevis’ formula between GPS PWV with radiosonde method shows a high correlation. The results of this GPS measurement experiment are helpful both for accumulating the study of precipitable water vapor derived from GPS in Chengdu areas located at the eastern flank of the Tibetan Plateau and for studying spatial-temporal variations of regional atmospheric water vapor and for applying in nowcasting, usage of atmospheric water resources and weather modification through many disciplines cooperatively.(4) The temporal variation and spatial difference of GPS-derived precipitable water in different climatic regions or under the influence of different topography, the relationships among GPS PWV and surface pressure, air temperature, vapor pressure and precipitation, and the variation features of GPS PWV in rainfall processes are studied deeply. The emphasis is on the diurnal cycle of GPS PWV and the relations to the peculiarity of local circulation and rainfall.The diurnal variations of water vapor in Kanto Plain of central Japan (as the first experimental region in this study) under the background of ocean monsoon climate are investigated with GPS-derived precipitable water and surface meteorological data as classified to three kinds of locations (mountainous area, basin, and plain-coast). The GPS PWV shows a clear diurnal cycle. The daily amplitude of GPS PWV is the largest in basin and the smallest in plain. A typical feature of the diurnal variation of GPS PWV in central Japan is a maximum appearing in the evening. The results suggest that the diurnal variation of GPS PWV seems to be strongly affected by the local thermal circulations generated by the topography around these stations. The moisture transport causes the differences in phase of the diurnal cycle of GPS PWV between different locations as well as the phase difference in precipitation. The precipitation observed frequently in the evening also shows a similar diurnal variation to that of the GPS PWV, indicating the peak of precipitation appearing in late afternoon or in the evening over central Japan. Meanwhile, the GPS PWV reaches its nocturnal maximum. There is a good relationship between the diurnal cycle of observed precipitation and that of the GPS PWV.Moreover, the diurnal variations of water vapor in Chengdu Plain (as the second experimental region in this study) under the influence of subtropical monsoon humid climate are preliminarily investigated with surface meteorological data and GPS PWV from the first experiment of remote sensing local precipitable water vapor by using ground-based regional GPS network. The diurnal variations of GPS PWV and some surface meteorological elements are composite during the warm days at Chengdu and Pixian in the basin climatic region in the eastern flank of the Tibetan Plateau. The GPS PWV in the midsummer stable weather shows a clear diurnal cycle with the amplitude and changes obviously in day and little at night. A typical feature of the diurnal variation at Chengdu and Pixian is a maximum appears in late afternoon, a minimum appears in early morning. The comparison of GPS PWV and rainfall shows that there is a good correlation between them in calm warm season. The precipitating is observed frequently in the evening. After GPS PWV reaches its maximum in the late afternoon, main rainfall process will occur, which leads to a remarkable decrease of GPS PWV and a rapid rise of surface water vapor. When the drop of GPS PWV is stable, the main rainfall process will stop. The accumulating and releasing processes of GPS PWV is also well related with rainfall, its increase or decrease continuously suggests the beginning or end of rainfall, respectively.Finally, based on the data of PWV derived from ground-based GPS networks and rainfall data from AWS in Chengdu and North China, the variational features of GPS PWV in several typical cases of heavy rainfall processes are analyzed, the results are help to obtain some index which can be used in the forecast of rainy weather, especially for the short forecast and nocasting of heavy rain.更多还原