Stable isotope composition of waters in the Great Basin, United States 1. Air-mass trajectories
Stable isotope composition of waters in the Great Basin, United States 1. Air-mass trajectories
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DOI：
10.1029/2001jd000565
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发表时间：
2002-10
影响因子：
--
通讯作者：
I. Friedman;J. Harris;George I. Smith;C. Johnson
中科院分区：
文献类型：
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作者：
I. Friedman;J. Harris;George I. Smith;C. Johnson
[1] 使用 NOAA/气候监测和诊断实验室的等熵输运模型计算出的等熵轨迹，用于确定气团的起源以及气团轨迹对 1991 年 10 月至 1993 年 9 月期间在犹他州锡达城和内华达州温尼马卡发生的降水事件同位素组成的影响。对追踪空气团位置 10 天的轨迹进行检查，发现了五个不同的水蒸气起源区域：(1) 阿拉斯加湾和北太平洋，(2) 中部太平洋，(3) 热带太平洋，(4) 墨西哥湾，以及 (5) 大陆陆地。氘 (δD) 和氧 18 (δ18O) 分析是对占所有雪松城事件 99% 的降水进行的。对占温尼马卡同期降水量 66% 的降水量进行了类似的分析。确定了来自每个水蒸气源的降水的平均同位素组成。研究期间，两个地点的降水量一半以上源自热带太平洋，并向东北方向移动至大盆地；只有一小部分人穿越了内华达山脉。降水的同位素组成由气团起源及其到收集站的轨迹、液滴形成机制、云内重新平衡以及从云到地面过程中的蒸发决定。瑞利蒸馏模型可以解释当气团在上升过程中伪绝热冷却时降水同位素组成的变化。然而，在大盆地常见的积雨云和其他云的快速对流环境中发生的复杂过程，特别是在夏季，需要修改该模型，因为在这些云的下部形成的雨滴在上升到云的上层并最终落到地面时会发生同位素变化。
[1] Isentropic trajectories, calculated using the NOAA/Climate Monitoring and Diagnostics Laboratory's isentropic transport model, were used to determine air-parcel origins and the influence of air mass trajectories on the isotopic composition of precipitation events that occurred between October 1991 and September 1993 at Cedar City, Utah, and Winnemucca, Nevada. Examination of trajectories that trace the position of air parcels backward in time for 10 days indicated five distinct regions of water vapor origin: (1) Gulf of Alaska and North Pacific, (2) central Pacific, (3) tropical Pacific, (4) Gulf of Mexico, and (5) continental land mass. Deuterium (δD) and oxygen-18 (δ18O) analyses were made of precipitation representing 99% of all Cedar City events. Similar analyses were made on precipitation representing 66% of the precipitation falling at Winnemucca during the same period. The average isotopic composition of precipitation derived from each water vapor source was determined. More than half of the precipitation that fell at both sites during the study period originated in the tropical Pacific and traveled northeast to the Great Basin; only a small proportion traversed the Sierra Nevada. The isotopic composition of precipitation is determined by air-mass origin and its track to the collection station, mechanism of droplet formation, reequilibration within clouds, and evaporation during its passage from cloud to ground. The Rayleigh distillation model can explain the changes in isotopic composition of precipitation as an air mass is cooled pseudo-adiabatically during uplift. However, the complicated processes that take place in the rapidly convecting environment of cumulonimbus and other clouds that are common in the Great Basin, especially in summer, require modification of this model because raindrops that form in the lower portion of those clouds undergo isotopic change as they are elevated to upper levels of the clouds from where they eventually drop to the ground.