Analytic Parameterization of Longwave Optical Properties of Bulk Vegetation Layer Permitting Non-Zero Leaf Reflectivity and Its Implementation in CLM5

IF 4.4 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES
Hyeon-Ju Gim, Seon Ki Park
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引用次数: 0

Abstract

For modern land surface models (LSMs) representing a singular bulk vegetation layer, the longwave optical properties (i.e., emissivity, reflectivity, and transmittivity) of vegetation layer are derived with a simplified constraint of assuming zero leaf reflectivity. This constraint is necessary, for instance, to the Beer–Lambert (B–L) law to establish a relationship between the optical properties and leaf area index. However, the simplified constraint leads to an overestimation of land surface emissivity in the vegetated regions. In this study, we introduce a new scheme considering realistic leaf reflectivity values rather than assuming zero. This new scheme is based on the relationship derived from the B–L law, but it is statistically augmented to consider the effects of leaf reflections. It is designed to emulate a multi-vegetation-layer numerical model known as the Norman model, which is capable of numerical calculations of multi-reflections among leaves. This new method consists of only a couple of simple equations; despite its simplicity, it very closely mimics the Norman model; The discrepancy of the results between the new method and the Norman model is less than measurement uncertainties for any combination of input parameters. When the new scheme is implemented in the Community Land Model version 5 (CLM5), the land surface emissivity values are simulated much more consistently with global measurements, resulting in significant alterations of land surface energy budget. The enhanced realism through our new scheme is poised to contribute to more accurate numerical weather and climate simulations.

Abstract Image

允许非零叶片反射率的大体积植被层长波光学特性分析参数化及其在 CLM5 中的应用
现代地表模型(LSMs)表示单一的植被层,植被层的长波光学特性(即发射率、反射率和透射率)是在假定叶片反射率为零的简化约束条件下得出的。例如,这种约束对于比尔-朗伯(B-L)定律来说是必要的,它可以建立光学特性与叶面积指数之间的关系。然而,简化约束会导致高估植被区的地表发射率。在本研究中,我们引入了一种新方案,考虑到实际的叶片反射率值,而不是假设为零。这一新方案以 B-L 法则的关系为基础,但考虑到叶片反射的影响,对其进行了统计增强。它的设计目的是模拟一种称为诺曼模型的多植被层数值模型,该模型能够对树叶间的多重反射进行数值计算。在任何输入参数组合下,新方法与诺曼模型之间的结果差异都小于测量不确定性。将新方案应用于社区土地模型 5(CLM5)版本时,模拟的地表发射率值与全球测量值更加一致,从而显著改变了地表能量预算。我们的新方案增强了真实性,有望为更精确的天气和气候数值模拟做出贡献。
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来源期刊
Journal of Advances in Modeling Earth Systems
Journal of Advances in Modeling Earth Systems METEOROLOGY & ATMOSPHERIC SCIENCES-
CiteScore
11.40
自引率
11.80%
发文量
241
审稿时长
>12 weeks
期刊介绍: The Journal of Advances in Modeling Earth Systems (JAMES) is committed to advancing the science of Earth systems modeling by offering high-quality scientific research through online availability and open access licensing. JAMES invites authors and readers from the international Earth systems modeling community. Open access. Articles are available free of charge for everyone with Internet access to view and download. Formal peer review. Supplemental material, such as code samples, images, and visualizations, is published at no additional charge. No additional charge for color figures. Modest page charges to cover production costs. Articles published in high-quality full text PDF, HTML, and XML. Internal and external reference linking, DOI registration, and forward linking via CrossRef.
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