Comprehensive Study on Meso-Scale Precipitation System with Use of Stable Isotope Ratios of Water

2004年冲绳雨季，利用偏振多普勒雷达和GPS探空仪对降水进行了几分钟间隔的氧同位素组成分析和气象观测。大的同位素变化观察到的事件到事件的降水，尽管相同的蒸汽来源，这意味着降水类型（对流或层状）显着影响同位素值。对流系统发展前对流层中层的干燥对对流降水同位素变化有很大影响，对流降水同位素变化的事件内分析发现对流系统发展阶段与对流降水同位素值有很强的相关性。对流系统发展阶段，同位素值呈逐渐降低的趋势，而消散阶段，同位素值呈V形分布。这些“V”型模式可能是由于下落的雨滴大量蒸发造成的。 ...更多信息 为定量评价雨滴降落过程中同位素的变化，提出了“不同粒径雨滴与水汽同位素交换模型”。作为敏感性实验的结果，同位素位移较大，在较小的雨滴或在较低的相对湿度。结果表明，云底以下相对湿度是影响降水同位素值的重要控制因子，采用液氮收集雨滴的方法和微量水样的同位素分析，观测了降水同位素值的滴径分布。对2007年名古屋3次降水过程的观测结果表明，降水中氢氧同位素值在较小的雨滴中较高，这与模式计算结果相一致，表明降水同位素组成的变化应考虑云型的差异和雨滴下落过程中的蒸发作用，而不仅仅是如前所述的蒸汽源的差异。少

Analyses of oxygen isotopic composition of precipitation with several minutes intervals and meteorological observation by a polarimetric Doppler radar and GPS sondes were conducted during rainy season in 2004 at Okinawa. Large isotopic variation observed in event-to-event precipitation, in spite of the same vapor origins, implied that precipitation type (convective or stratiform) significantly affected isotopic values. Moreover, isotopic variation during convective precipitation was strongly affected by dryness in the middle troposphere before development of the convective system.Based on the intra-event analyses of isotopic variation, it was found that the development stage of convective systems strongly related to isotopic values. Isotopic values showed gradual decreasing trends in the developing stage, whereas they showed V-shape patterns in the dissipating stage of convective systems. These V-shape patterns could be caused by significant evaporation of falling raindrops.For quantit … More ative evaluation of isotopic change during raindrop falling, "isotopic exchange model of between raindrop and vapor for each size" was developed. As a result of sensitivity experiment, isotopic shifts were larger in smaller raindrops or at lower relative humidity. It could be demonstrated that relative humidity below cloud base was a significant controlling factor for the isotopic values of bulk(weighted mean)precipitation.Drop-size distribution of isotopic values in precipitation, which was expected from the model simulation, was observed by a raindrop collection method using liquid nitrogen and the isotope analysis for micro-liter of water samples. All observed results of three rainfall events at Nagoya in 2007 showed that higher hydrogen and oxygen isotopic values were found in smaller raindrops, which were consistent with the model calculation.Our results clearly indicate that the difference of cloud types and the evaporation effect during falling raindrops should be taken into account for the variation of isotopic composition of precipitation, not only the difference of vapor sources as discussed previously. Less