Representing 3-D cloud radiation effects in two-stream schemes: 2. Matrix formulation and broadband evaluation
Representing 3-D cloud radiation effects in two-stream schemes: 2. Matrix formulation and broadband evaluation
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DOI：
10.1002/2016jd024875
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发表时间：
2016-07-27
影响因子：
4.4
通讯作者：
Mayer, Bernhard
中科院分区：
文献类型：
--
作者：
Hogan, Robin J.;Schafer, Sophia A. K.;Mayer, Bernhard
由于缺乏一种适用于全球大气模式的快速辐射方案，无法在短波和长波中同时表示这些影响，因此无法估计通过云侧的辐射输送对全球能量收支的影响。这篇由两部分组成的论文描述了这种方案的发展，我们称之为通过云层辐射传输的快速算法（SPARTACUS）。该方法的原理是在两流方程中添加额外的项来表示晴空和多云区域之间的横向传输，这些项与云边缘的长度成比例地变化，作为高度的函数。本文描述了用矩阵指数法求解短波和长波耦合方程组的一种鲁棒而精确的方法。该求解器已与气体吸收的相关k模型耦合。然后，我们通过将SPARTACUS与蒙特卡罗模型MYSTIC对云场的全三维辐射计算进行宽带比较，确认了SPARTACUS的准确性，特别检查了引入三维效应时云辐射效应（CRE）的百分比变化。在短波中，斯巴达克斯正确地捕捉到了CRE的变化，CRE随太阳天顶角在-25%到+120%之间变化。在长波中，SPARTACUS很好地捕获了云的辐射冷却的增加，尽管如果对云集群进行近似校正，它只能正确地模拟表面CRE增加30%（约4Wm(-2)）。
Estimating the impact of radiation transport through cloud sides on the global energy budget is hampered by the lack of a fast radiation scheme suitable for use in global atmospheric models that can represent these effects in both the shortwave and longwave. This two-part paper describes the development of such a scheme, which we refer to as the Speedy Algorithm for Radiative Transfer through Cloud Sides (SPARTACUS). The principle of the method is to add extra terms to the two-stream equations to represent lateral transport between clear and cloudy regions, which vary in proportion to the length of cloud edge as a function of height. The present paper describes a robust and accurate method for solving the coupled system of equations in both the shortwave and longwave in terms of matrix exponentials. This solver has been coupled to a correlated-k model for gas absorption. We then confirm the accuracy of SPARTACUS by performing broadband comparisons with fully 3-D radiation calculations by the Monte Carlo model MYSTIC for a cumulus cloud field, examining particularly the percentage change in cloud radiative effect (CRE) when 3-D effects are introduced. In the shortwave, SPARTACUS correctly captures this change to CRE, which varies with solar zenith angle between -25%and +120%. In the longwave, SPARTACUS captures well the increase in radiative cooling of the cloud, although it is only able to correctly simulate the 30% increase in surface CRE (around 4Wm(-2)) if an approximate correction is made for cloud clustering.