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arXiv 1301.3083physics.ao-phq-bio.QM
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为什么森林上空的气流会产生更多的雨水?降雨、气压和大气湿度之间的耦合关系

Why does air passage over forest yield more rain? Examining the coupling between rainfall, pressure and atmospheric moisture content

Anastassia M. Makarieva, Victor G. Gorshkov, Douglas Sheil, Antonio D. Nobre, Peter Bunyard, Bai-Lian Li

摘要:

森林损失对降雨量的影响仍然知之甚少。为了应对这一挑战,Spracklen等人最近提出了一项关于降雨量和土地覆盖的泛热带研究,该研究表明,卫星得出的降雨量测量与模型得出的空气轨迹暴露于森林覆盖的程度呈正相关。这一结果证实了植被对区域降雨模式的影响,在以前的研究中建议。然而,我们发现,Spracklen等人的结论--降雨量的差异反映了蒸散造成的空气水分含量,而环流模式保持不变--似乎受到方法不一致的影响。我们确定的基础分析和预测的降雨量变化的定量估计,如果森林覆盖在亚马逊地区丢失的方法学问题。我们讨论了一些替代的解释,其中包括森林蒸散的独特作用,在创建低压系统,从海洋到大陆腹地的水分。我们的分析,从三个地区在巴西,包括亚马逊森林,揭示了一种趋势,雨天在雨季柱水蒸气(CWV)超过50毫米,有较高的压力比无雨天,而在较低的CWV雨天往往有较低的压力比无雨天。大气水分含量和循环动力学之间的耦合突出表明,森林损失所造成的危险比仅仅关注水分循环所表明的危险更大。

英文摘要:

The influence of forest loss on rainfall remains poorly understood. Addressing this challenge Spracklen et al. recently presented a pan-tropical study of rainfall and land-cover that showed that satellite-derived rainfall measures were positively correlated with the degree to which model-derived air trajectories had been exposed to forest cover. This result confirms the influence of vegetation on regional rainfall patterns suggested in previous studies. However, we find that the conclusion of Spracklen et al. -- that differences in rainfall reflect air moisture content resulting from evapotranspiration while the circulation pattern remains unchanged -- appears undermined by methodological inconsistencies. We identify methodological problems with the underlying analyses and the quantitative estimates for rainfall change predicted if forest cover is lost in the Amazon. We discuss some alternative explanations that include the distinct role of forest evapotranspiration in creating low pressure systems that draw moisture from the oceans to the continental hinterland. Our analysis of meteorological data from three regions in Brazil, including the central Amazon forest, reveal a tendency for rainy days during the wet season with column water vapor (CWV) exceeding 50 mm to have higher pressure than rainless days; while at lower CWV rainy days tend to have lower pressure than rainless days. The coupling between atmospheric moisture content and circulation dynamics underlines that the danger posed by forest loss is greater than suggested by focusing only on moisture recycling alone.

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