A new two-moment bulk stratiform cloud microphysics scheme in the Community Atmosphere Model, version 3 (CAM3). Part I: Description and numerical tests
A new two-moment bulk stratiform cloud microphysics scheme in the Community Atmosphere Model, version 3 (CAM3). Part I: Description and numerical tests
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DOI：
10.1175/2008jcli2105.1
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发表时间：
2008-08
影响因子：
4.9
通讯作者：
H. Morrison;A. Gettelman
中科院分区：
文献类型：
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作者：
H. Morrison;A. Gettelman
本文介绍一个新的大气环流模式中的二阶矩层状云微物理方案。预测变量包括云滴和云冰质量混合比和数量浓度。该方案处理几个微物理过程，包括水凝物收集，冷凝/蒸发，冻结，熔化和沉积。气溶胶上液滴的激活是基于物理的，并与亚网格垂直速度相耦合。该方案的独特之处，相对于现有的两个时刻的方案开发的大气环流模式，是诊断治疗的雨和雪数浓度和混合比和显式治疗的次网格云水变率的微物理过程率的计算。该计划的数值方面进行了详细描述，使用理想化的一维离线测试的微观物理。时间步长，垂直分辨率，诊断降水的数值方法的方案的敏感性进行了研究在一系列的条件。据发现，在一般情况下，需要两个子步骤的数值稳定性和合理的小时间截断误差使用的时间步长为20分钟，然而，子步只需要降水微物理过程，而不是整个计划。与基准模拟相比，诊断雨雪的新数值方法产生合理的结果，特别是在低垂直分辨率下。本研究的第二部分详细介绍了该方案在单柱和全球模拟中的结果，包括与观测结果的比较。
A new two-moment stratiform cloud microphysics scheme in a general circulation model is described. Prognostic variables include cloud droplet and cloud ice mass mixing ratios and number concentrations. The scheme treats several microphysical processes, including hydrometeor collection, condensation/ evaporation, freezing, melting, and sedimentation. The activation of droplets on aerosol is physically based and coupled to a subgrid vertical velocity. Unique aspects of the scheme, relative to existing two-moment schemes developed for general circulation models, are the diagnostic treatment of rain and snow number concentration and mixing ratio and the explicit treatment of subgrid cloud water variability for calculation of the microphysical process rates. Numerical aspects of the scheme are described in detail using idealized one-dimensional offline tests of the microphysics. Sensitivity of the scheme to time step, vertical resolution, and numerical method for diagnostic precipitation is investigated over a range of conditions. It is found that, in general, two substeps are required for numerical stability and reasonably small time truncation errors using a time step of 20 min; however, substepping is only required for the precipitation microphysical processes rather than the entire scheme. A new numerical approach for the diagnostic rain and snow produces reasonable results compared to a benchmark simulation, especially at low vertical resolution. Part II of this study details results of the scheme in single-column and global simulations, including comparison with observations.