Incorporating the Effects of 3D Radiative Transfer in the Presence of Clouds into Two-Stream Multilayer Radiation Schemes
Incorporating the Effects of 3D Radiative Transfer in the Presence of Clouds into Two-Stream Multilayer Radiation Schemes
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DOI：
10.1175/jas-d-12-041.1
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发表时间：
2013-02-01
影响因子：
3.1
通讯作者：
Shonk, Jonathan K. P.
中科院分区：
文献类型：
--
作者：
Hogan, Robin J.;Shonk, Jonathan K. P.
本文提出了一种新方法来表示双流辐射方案中穿过云侧的水平辐射传输的重要影响。通常，辐射传输方程针对每个模型级别内的晴朗和阴天区域分别进行离散化，但这里引入了表示区域之间横向辐射交换的术语，并且针对每个层求解所得的耦合方程。这种方法可以适用于直接入射的短波辐射（受比尔定律控制）和漫射短波和长波辐射（受双流方程控制）。横向交换率由云“边缘”的面积决定。通过与文献中针对 3D 效应较强的两种云类型（特别是积云和飞机尾迹）的严格 3D 辐射传输计算进行比较，证明了该方法的有效性。对短波云辐射强迫的 3D 影响在 -25% 和 +100% 之间变化，具体取决于太阳天顶角。即使云的表示非常简单，新方案也与短波中的严格计算表现出良好的一致性，为在气候模型中有效而准确地表示这一重要效应开辟了道路。
This paper presents a new method for representing the important effects of horizontal radiation transport through cloud sides in two-stream radiation schemes. Ordinarily, the radiative transfer equations are discretized separately for the clear and cloudy regions within each model level, but here terms are introduced that represent the exchange of radiation laterally between regions and the resulting coupled equations are solved for each layer. This approach may be taken with both the direct incoming shortwave radiation, which is governed by Beer's law, and the diffuse shortwave and longwave radiation, governed by the two-stream equations. The rate of lateral exchange is determined by the area of cloud "edge." The validity of the method is demonstrated by comparing with rigorous 3D radiative transfer calculations in the literature for two cloud types in which the 3D effect is strong, specifically cumulus and aircraft contrails. The 3D effect on shortwave cloud radiative forcing varies between around -25% and around +100%, depending on solar zenith angle. Even with an otherwise very simplistic representation of the cloud, the new scheme exhibits good agreement with the rigorous calculations in the shortwave, opening the way for efficient yet accurate representation of this important effect in climate models.