地基GPS遥感的成都地区夏季可降水量的日循环合成分析

Composite study of diurnal cycle of precipitable water vapor derived from ground-based GPS in Chengdu Plain during the warm season

利用成都地基全球定位系统（GPS）观测网2004年7—9月的观测数据，结合自动气象站获得的气象资料计算出GPS遥感的可降水量（PWV）。与气象探空站观测资料算出的可降水量进行对比，确定出本次GPS遥感可降水量的精度为3．09mm。并对成都、郫县夏季PWV的日循环特征进行了合成分析。结果表明：PWV呈明显的日循环，最小值出现在8：00（北京时间），成都和郫县分别为40．5mm和35．0mm；最大值出现在17：00左右，成都和郫县分别为43．5mm和38．0mm。白天PWV的变化较大，夜间相对稳定，日变幅为3mm。在盛夏静稳型天气下，成都地区的PWV日循环特征与地面气温基本一致，皆受太阳辐射日变化的控制。降水日变化的一个显著特点是降水主要发生在夜间，当PWV在下午达到最大之后，主降水阶段开始，使PWV明显减少，同时使地面空气比湿迅速增大；当PWV下降到一个稳定状态后，主降水过程随之结束。大气水汽总量的积累和释放与地面降水有较好的对应关系，PWV的持续性递增和持续性递减预示着降水的开始和结束。

In this study, the hydrological cycle especially diurnal cycle of the precipitable water vapor derived from GPS （ PWV GPS） is investigated based on the ground-based the GPS observation experiment and automatic weather stations in the Chengdu Plain of southwest China during the period of July to September 2004. The comparison of the PWV GPS and those from radiosonde observations is given at Chengdu station, with the RMS （Root Mean Square） differences of 3.09 mm. This is surprisingly small considering the distance of up to several tens of kilometers between radiosonde station and closest GPS site. The diurnal variations of water vapor in Chengdu Plain were preliminarily investigated with the PWV GPS and the surface meteorological data. The diurnal variations of the PWV and some surface meteorological elements were composite during the warm days at Chengdu and Pixian. The PWV GPS showed a clear diurnal cycle with the amplitude of about 3 mm and changed obviously in day and little at night. A typical feature of the diurnal variation at Chengdu and Pixian is that the maximum, 43.5 mm and 38.0 mm, respectively, appeared in late afternoon, and the minimum, 40.5mm and 35.0mm, respectively appeared in early morning. The variation period of PWVGPS is similar to that of surface temperature, they are all controlled by the diur- nal variation of solar radiation. The comparison of the PWVGPS and the rainfall shows that there is a good correlation between them in the calm warm season. The precipitating is observed frequently in the evening. The main rainfall process will oocur after the PWVGPS reaches its maximum in the late afternoon, which leads to a remarkable decrease of the PWV GPS and a rapid rise of surface water vapor. When the drop of the PWV GPS is stable, the main rainfall process will stop. The accumulating and releasing processes of the PWVGPS is also well related to the rainfall, its increase or decrease continuously suggests the beginning or the end of the rainfall, respectively.