Stable isotope ratios in precipitation and their relationship with meteorological conditions in the Kumaon Himalayas, India
Stable isotope ratios in precipitation and their relationship with meteorological conditions in the Kumaon Himalayas, India
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DOI：
10.1016/j.jhydrol.2010.06.019
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发表时间：
2010-09
影响因子：
6.4
通讯作者：
U. Kumar;B. Kumar;S. Rai;S. Sharma
中科院分区：
文献类型：
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作者：
U. Kumar;B. Kumar;S. Rai;S. Sharma
环境同位素(δ2H，δ18O，3H)数据主要基于印度库曼喜马拉雅山脉的降水样本，首次被用来了解控制该地区降雨过程的各种气象因素的影响。此外，这些数据还被用来了解降水中的地形效应和估计降水中稳定同位素比值的海拔效应等。对同位素数据的解释表明，库马喜马拉雅地区冬季(10-2月)和夏季(5月)降水的水汽来源主要来自西方扰动，而其余时期的水汽来源则是季风(西南)。季风季局地降水中的δ-2-Η−δ-18O关系具有明显的季节效应，斜率为7.6.冬季和夏季降水样本比西南季风样本测得更高的环境湿度，因此表明大陆蒸发的水分。海拔影响的范围很广(δ18O每100m海拔变化：−0.30‰[7-8月]；−0.57‰[9月])，平均海拔效应分别为−2.61‰和−0.36‰/100m海拔，δ2H和δ18O。这些值不同于早先根据泉水/河流样本的同位素组成报告的该地区的值。连续降水中的“高度效应”基本上是一种与温度有关的现象，并根据与绝热冷却有关的降水过程(湿气团的干绝热递减率、湿绝热递减率和饱和绝热递减率)来解释。在δ2Η的情况下，高度效应被发现是更可靠的，因为氘受二次蒸发的影响最小。观测到了二次蒸发对真正的“高度效应”的影响。降雨的二次蒸发增加了氧同位素比值，这种增加与雨滴通过空气的垂直距离成正比。
For the first time, environmental isotopic (δ2H, δ18O,3H) data, predominantly based on precipitation samples in the Kumaon Himalayas, India, have been used to understand the influence of various meteorological factors governing rainout processes in the region. Further, the data are also used to understand the orographic effects in precipitation and to estimate the altitude effect in stable isotopic ratios in precipitation, etc. The interpretation of the isotopic data revealed that the source of moisture for winter (October–February) and summer (May) precipitation in the Kumaon Himalayas is mainly from the Western Disturbances whereas for the remaining period the source is monsoonal (southwest). The δ2Η−δ18O relationship in the local precipitation during the monsoon season shows a distinct seasonal effect, with a slope of 7.6. The winter and summer precipitation samples measured higher environmental3H compared to southwest monsoon samples, thus indicating continental evaporated moisture. There is wide range of altitude effects (δ18O variation per 100m elevation: −0.30‰ [July–August]; −0.57‰ [September]) with the mean altitude effect being −2.61‰ and −0.36‰ per 100m elevation for δ2H and δ18O respectively. These values are different from that reported earlier for the region based on the isotopic compositions of springs/rivers samples. The ‘altitude effect’ in successive precipitation is basically a temperature dependent phenomenon and is explained on the basis of adiabatic cooling related rainout process (dry adiabatic lapse rate, moist adiabatic lapse rate and saturated adiabatic lapse rate for moist air mass). The altitude effect is found to be more reliable in case of δ2Η, as deuterium is least affected by secondary evaporation. The effect of secondary evaporation has been observed on the true “altitude effect”. Secondary evaporation of rainfall increases the oxygen isotopic ratios and the increase is directly proportional to the vertical distance travelled by the raindrops through air.