Studies with a flexible new radiation code .1. Choosing a configuration for a large-scale model
Studies with a flexible new radiation code .1. Choosing a configuration for a large-scale model
复制标题
DOI：
10.1002/qj.49712253107
复制
发表时间：
1996-04-01
影响因子：
8.9
通讯作者：
Slingo, A
中科院分区：
文献类型：
--
作者：
Edwards, JM;Slingo, A
基于长波和短波两个谱区的双流方程，建立了一个综合的新的辐射计算程序。该代码的光谱分辨率是可变的，使其能够在广泛的应用中使用。由于它的灵活性，该程序非常适合于研究辐射计算对物理过程参数化方式变化的敏感性。气体传输数据是从逐行模型导出的。特别注意水蒸气连续体的处理，气体之间的重叠，以及对二氧化碳浓度变化的敏感性。程序的性能在高光谱分辨率和为英国气象局联合预报/气候模式(UM)设计的低分辨率配置下进行了检验。尤其是在UM中使用时，必须证明代码在整个大气条件范围内都能令人满意地执行。因此，在晴天和多云的天空中，将长波和短波的计算与参考计算进行了比较，并研究了各种过程的表示精度。对于短波的计算，基于光学厚云反射率的解析表达式，提出了一种新的计算宽带单次散射特性的方法。当光谱分辨率降低到为UM设计的分辨率时，这将最大限度地减少计算水云的短波辐射特性的误差。相比之下，对于冰云，误差是最小的，通过使用线性平均来推导单次散射特性，对于光学薄云是合适的。在长波中，我们用高光谱分辨率研究了卷云中辐射加热的垂直分布。长波辐射的散射效应通常在大尺度模型中被忽略，本文对此进行了较为详细的研究，并用一个简单的模型对其进行了解释。考虑到所有这些研究，得出的结论是，为UM设计的配置保留了代码的一般性，而不会显著影响总体准确性。
A comprehensive new radiation code based on the two-stream equations in both the long-wave and short-wave spectral regions is described. The spectral resolution of the code is variable, enabling it to be used in a wide range of applications. Because of its flexibility, the code is well-suited to the investigation of the sensitivity of radiative calculations to changes in the way in which physical processes are parametrized. The gaseous transmission data are derived from a line-by-line model. Particular attention is directed towards the treatment of the water vapour continuum, the overlap between gases, and the sensitivity to changing the carbon dioxide concentrations.The performance of the code is examined both at high spectral resolution and in a lower-resolution configuration designed for the UK Meteorological Office United Forecast/Climate Model (UM). Particularly for use in the UM, the code must be shown to perform satisfactorily across the whole range of atmospheric conditions. Comparisons are therefore made with reference calculations in both the long-wave and the short-wave, in clear and cloudy skies, and the accuracy with which various processes may be represented is studied.For the cloudy calculations in the short-wave, a new method is presented for deriving the single-scattering properties in broad bands, based on the analytic expression for the reflectivity of an optically thick cloud. This minimizes the errors in calculating the short-wave radiative properties of water clouds when the spectral resolution is reduced to that designed for the UM. In contrast, for ice clouds the errors are minimized by deriving the single-scattering properties using linear averaging, as appropriate for optically thin clouds. In the long-wave, the vertical distribution of the radiative heating in cirrus clouds is examined at high spectral resolution. The effect of scattering of long-wave radiation, usually ignored in large-scale models, is examined in some detail and is explained using a simple model. Taking all these studies into account, it is concluded that the configuration designed for the UM retains the generality of the code, without significantly compromising the overall accuracy.