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Characteristics of GPS Vapor in a Persistent Heavy Rainfall Related to Southwest Vortex
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摘要: 利用成都地区地基GPS遥感的大气水汽总量资料 (GPS-PWV)、NCEP再分析资料、自动站降水量资料和探空站比湿资料，对2010年7月15—18日发生在四川盆地东北部的一次持续性暴雨的水汽变化特征进行综合分析，重点探究这次大暴雨的影响系统 (西南涡) 发生、发展前后GPS-PWV的演变特征及其与降水的关系。结果表明：降水发生时，GPS-PWV通常在短时间内有急剧的上升，并在西南涡形成前达到最大值；西南涡完全形成时，GPS-PWV急升结束；西南涡东移，GPS-PWV继续下降到最低，降水趋于结束。与水汽通量散度相比较，水汽散度垂直通量能更好地描述暴雨过程中的强上升、辐合辐散运动以及水汽输送情况，它与GPS-PWV变化趋势基本一致。因此，GPS-PWV的急升与陡降对大暴雨的形成与减弱有一定指示意义。Abstract: Using GPS Precipitable Water Vapor (GPS-PWV) observations from the ground-based GPS network in Chengdu Plain, NCEP reanalysis data, observed precipitation from automatic weather stations (AWS) and the specific humidity of single radiosonde station, the variations of water vapor in a persistent heavy rainfall process over the northeastern Sichuan Basin from 15 July to 18 July in 2010 is analyzed, focusing on the changes of GPS-PWV under the influencing system (southwest vortex) and its relationship with precipitation. Usually, there is a sharp rise of GPS-PWV when the precipitation occurs, and the altitude or terrain of each GPS station has an obvious impact on the value of GPS-PWV, precipitation and its peak. The GPS-PWV is not simple proportional related with the actual rainfall, the occurrence time and value of the precipitation have a certain relationship with the observatory sites and the movement of the southwest vortex. When the vortex circulation begins to develop, the instability of water vapor transport makes the GPS-PWV fluctuant increases. A large surge of GPS-PWV increase can be observed 13—17 h before the formation of the southwest vortex, reaching the maximum about 0—4 h before the vortex formation. The increase ends when it is fully formed, and the GPS-PWV gradually drops to the original level or even lower with the eastward shift of the southwest vortex. The positive area of the vertical flux of moisture divergence is well correspond with the area of precipitation, and it can better describe the strong rise, the movement of the convergence and divergence and water vapor transport than moisture flux divergence in the process, and the change of GPS-PWV is consistent with the vertical flux of moisture divergence. In addition, the trend of the water transport and convergence in the development process of the vortex circulation is consistent with the change of GPS-PWV, the surge and drop of GPS-PWV have some indicating significance in the formation or weakening of heavy rainfall. Compared with the radiosonde stations, AWS can well reflect the changes of water vapor near the ground, and radiosonde stations can provide the vertical distribution of the specific humidity. The regional ground-based GPS station network may capture the overall changes of the whole layer of atmospheric water vapor with the high time resolution. Therefore, more attention should be paid to the comprehensive application of water vapor information that obtained by these different observations means. Also, the southwest vortex as one of the major systems that induce the rainstorm process of the Sichuan Basin and the Yangtze Valley, adding to the important significance of GPS-PWV to discuss the variation of water vapor field before and after the generation of the southwest vortex.
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图 1 2010年7月NCEP再分析资料700 hPa位势高度场 (等值线，单位：gpm) 和风场 (矢量)
(a)16日14：00，(b)17日02：00
Fig. 1 700 hPa geopotential height (contour, unit: gpm) and wind (vector) from NCEP reanalysis
(a)1400 BT 16 July 2010, (b)0200 BT 17 July 2010
图 2 2010年7月15—19日成都地区GPS-PWV与降水量的逐时演变曲线
Fig. 2 Time series of GPS-PWV and precipitation in Chengdu from 15 July to 19 July in 2010
图 3 2010年7月16日06:00—17日05:00 GPS-PWV日平均值的空间分布 (单位：mm)
Fig. 3 Spatial distribution of daily average GPS-PWV from 0600 BT 16 July to 0500 BT 17 July in 2010(unit: mm)
图 4 2010年7月15—18日西南涡移动路径示意图
Fig. 4 Movement of southwest vortex from 15 July to 18 July in 2010
图 5 2010年7月17日02:00(a) 和08:00(b) NCEP再分析资料700 hPa水汽散度垂直通量
(单位：10-5g·cm-2·hPa-1·s-2)
Fig. 5 700 hPa moisture flux divergence from NCEP at 0200 BT (a) and 0800 BT (b) on 17 July 2010
(unit:10-5g·cm-2·hPa-1·s-2)
图 6 2010年7月15日06:00—19日06:00自动气象站地面比湿的时间演变
Fig. 6 Evolution of specific humidity of automatic weather station from 0600 BT 15 July to 0600 BT 19 July in 2010
图 7 2010年7月16日20:00和17日20:00温江站的比湿廓线
Fig. 7 Distribution of specific humidity profile at Wenjiang Station at 2000 BT 16 July and 2000 BT 17 July in 2010
表 1 GPS-PWV急升时间、增幅、极值和西南涡降水情况
Table 1 The extremum, amplitude and duration of GPS-PWV with the rainfall of southwest vortex
站点 GPS-PWV急升持续
时间/h (有降水发生)GPS-PWV
增幅/mmGPS-PWV
极值/mm过程降水量
/mm小时最大
降水量/mm蒲江 15 26.0 62.6 95.4 33.8 大邑 6 15.4 44.8 42.0 29.3 成都 15 27.6 59.6 21.7 10.7 龙泉驿 8 10.9 49.2 10.1 6.5 都江堰 17 25.8 71.4 5.9 1.7 
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