Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 2. Physical interpretation of the amount effect
Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 2. Physical interpretation of the amount effect
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DOI：
10.1029/2008jd009943
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发表时间：
2008-10
影响因子：
--
通讯作者：
C. Risi;S. Bony;F. Vimeux
中科院分区：
文献类型：
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作者：
C. Risi;S. Bony;F. Vimeux
[1]在热带地区，降水中较重水同位素的比例与降水量呈反相关关系。这种所谓的数量效应背后的物理过程仍然很难理解和量化。本研究在包含Emanuel对流参数化的单柱模型中引入了稳定水同位素（H218O和HDO）。我们研究了数量效应背后的物理过程，并提出了一种量化其相对贡献的方法。我们关注对流过程，因为单柱模式的理想框架不允许我们考虑不同同位素特征的气团的大尺度水平平流的影响。结果表明，两种过程主要解释了降水的量效应：第一，降雨的再蒸发和与周围水汽的扩散交换；第二，通过对流通量补给对流系统的下层水汽的再循环。这突出了详细描述降雨蒸发过程对精确模拟热带降水同位素组成的重要性。利用热带海洋-全球大气-海洋-大气耦合响应实验（TOGA-COARE）活动的一维模拟，还研究了同位素组成在不同时间尺度（从天到月）上的变率。量效应在季节内或更长的时间尺度上最容易观察到。对流活动显著影响降水同位素组成的时间与大气水库中水的停留时间有关。
[1] In the tropics, the proportion of heavier water isotopes in precipitation is anticorrelated with the precipitation amount. The physical processes underlying this so-called amount effect are still poorly understood and quantified. In the present study, stable water isotopes (H218O and HDO) have been introduced in a single column model including the Emanuel convection parameterization. We investigate the physical processes underlying the amount effect and propose a methodology to quantify their relative contributions. We focus on convective processes, since the idealized framework of the single column models does not allow us to consider the effects of large-scale horizontal advections of air masses of different isotopic signatures. We show that two kinds of processes predominantly explain the amount effect: first, the reevaporation of the falling rain and the diffusive exchanges with the surrounding vapor; and second, the recycling of the subcloud layer vapor feeding the convective system by convective fluxes. This highlights the importance of a detailed representation of rain evaporation processes to simulate accurately the isotopic composition of precipitation in the tropics. The variability of the isotopic composition on different timescales (from days to months) is also studied using a unidimensional simulation of the Tropical Ocean–Global Atmosphere–Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) campaign. The amount effect is best observable at intraseasonal or longer timescales. The period of time over which convective activity significantly affects the isotopic composition of precipitation is related to the residence time of water within atmospheric reservoirs.