Froehlich Klaus, Kralik Martin, Papesch Wolfgang, Rank Dieter, Scheifinger Helfried, Stichler Willibald
Viktor-Wittner-Gasse 36/7, Vienna, Austria (IAEA Vienna).
Isotopes Environ Health Stud. 2008 Mar;44(1):61-70. doi: 10.1080/10256010801887208.
The paper evaluates long-term seasonal variations of the deuterium excess (d-excess = delta(2)H - 8. delta(18)O) in precipitation of stations located north and south of the main ridge of the Austrian Alps. It demonstrates that sub-cloud evaporation during precipitation and continental moisture recycling are local, respectively, regional processes controlling these variations. In general, sub-cloud evaporation decreases and moisture recycling increases the d-excess. Therefore, evaluation of d-excess variations in terms of moisture recycling, the main aim of this paper, includes determination of the effect of sub-cloud evaporation. Since sub-cloud evaporation is governed by saturation deficit and distance between cloud base and the ground, its effect on the d-excess is expected to be lower at mountain than at lowland/valley stations. To determine quantitatively this difference, we examined long-term seasonal d-excess variations measured at three selected mountain and adjoining valley stations. The altitude differences between mountain and valley stations ranged from 470 to 1665 m. Adapting the 'falling water drop' model by Stewart [J. Geophys. Res., 80(9), 1133-1146 (1975).], we estimated that the long-term average of sub-cloud evaporation at the selected mountain stations (altitudes between about 1600 and 2250 m.a.s.l.) is less than 1 % of the precipitation and causes a decrease of the d-excess of less than 2 per thousand. For the selected valley stations, the corresponding evaporated fraction is at maximum 7 % and the difference in d-excess ranges up to 8 per thousand. The estimated d-excess differences have been used to correct the measured long-term d-excess values at the selected stations. Finally, the corresponding fraction of water vapour has been estimated that recycled by evaporation of surface water including soil water from the ground. For the two mountain stations Patscherkofel and Feuerkogel, which are located north of the main ridge of the Alps, the maximum seasonal change of the corrected d-excess (July/August) has been estimated to be between 5 and 6 per thousand, and the corresponding recycled fraction between 2.5-3 % of the local precipitation. It has been found that the estimated recycled fractions are in good agreement with values derived from other approaches.
本文评估了奥地利阿尔卑斯山主脊南北两侧站点降水中氘过剩值（d-过剩 = δ²H - 8·δ¹⁸O）的长期季节变化。结果表明，降水期间的云下蒸发和大陆水分再循环分别是控制这些变化的局部和区域过程。一般来说，云下蒸发减少，水分再循环增加d-过剩值。因此，本文的主要目的是从水分再循环的角度评估d-过剩值的变化，这包括确定云下蒸发的影响。由于云下蒸发受饱和亏缺以及云底与地面之间距离的控制，预计其对d-过剩值的影响在山区要低于低地/山谷站点。为了定量确定这种差异，我们研究了在三个选定的山区和相邻山谷站点测量的长期季节d-过剩值变化。山区和山谷站点之间的海拔差异在470至1665米之间。采用Stewart [《地球物理研究杂志》，80(9)，1133 - 1146(1975)] 的 “落水滴” 模型，我们估计选定山区站点（海拔约1600至2250米）云下蒸发的长期平均值不到降水量的1%，导致d-过剩值减少不到2‰。对于选定的山谷站点，相应的蒸发比例最高为7%，d-过剩值的差异高达8‰。估计的d-过剩值差异已用于校正选定站点测量的长期d-过剩值。最后，估算了包括土壤水在内的地表水蒸发再循环的水汽相应比例。对于位于阿尔卑斯山主脊以北的两个山区站点帕茨尔科费尔山和费尔科格尔山，校正后的d-过剩值（7月/8月）的最大季节变化估计在5至6‰之间，相应的再循环比例为当地降水量的2.5 - 3%。研究发现，估计的再循环比例与其他方法得出的值高度一致。
