新的水云和冰云辐射参数方案的研究及其在气候模式中的应用

This project will study a new parameterization of radiative properties of liquid cloud and ice cloud and apply it in a global climate model (GCM) to improve the cloud-radiation process. Band-averaged optical properties of liquid cloud, which ignore the variations of the properties within each band and their correlation with gas absorption, are adopted in most of GCMs, resulting in errors in calculated cloud heating rate and the cloud radiative forcing. Firstly, a new correlated K-distribution parameterization of liquid cloud radiative properties, which takes into consideration the variation of the properties within each band, will be developed according to the correlation between the optical properties of water cloud and greenhouse gases. Secondly, radiative properties of ice cloud in current GCMs are generally based on the assumption that the crystals in ice cloud are all hexagonally shaped, which leads to large biases in calculated optical properties against reality, leading to an important source of uncertainty in climate simulations. Thus, new optical properties including the mixing of various crystal shapes will be obtained according to the updated spectral dataset for single crystal particle of various shapes, which will then be compared with previous results in similar studies. Thirdly, the above new radiative parameterizations of liquid and ice clouds combing 4-stream approximation radiation transfer method will be utilized in GCM to make validations and various climate simulation experiments, to improve the radiative transfer method in cloudy atmosphere and promote the overall simulation accuracy and level of cloud-radiation process in GCM.

本项目将研究新的水云和冰云的辐射参数化方案并应用到全球气候模式中来改进云辐射物理过程。目前世界上多数气候模式中普遍采用波带平均的水云光学性质，忽略了它们在波带内的变化和与气体的相关性，从而造成云的加热率和云辐射强迫的计算误差。首先，本项目将根据不同波带水云和温室气体的相关性，发展一种新的相关K-分布为基础的水云光学参数化方案，考虑它们在波段内的变化；其次，在目前气候模式冰云辐射参数化中，一般假定冰晶粒子为六棱柱形状，由此得来的冰云光学性质与实际有很大偏差，是气候模拟不确定的一个重要来源。本项目将根据最新的各种形状单个冰晶粒子光谱数据集，来获得考虑了不同形状冰云混合的总光学性质，并与以往同类研究结果比较；第三，将上述新的水云和冰云辐射参数化方案结合四流近似辐射传输方案应用于全球气候模式中进行检验和气候模拟试验，来改进有云大气的辐射传输和气候模式对云辐射过程的总体模拟精度和水平。

水云和冰云辐射参数化对辐射计算和气候模拟有重要的影响，并存在一定的不确定性。本项目根据不同波带水云和温室气体吸收特性的相关性，发展了一种新的以k分布为基础的水云光学参数化方案，考虑了水云光学性质在波段内的变化，并将其应用到气候模式中，详细分析了新方案对辐射和温度的影响。其次，根据包含多种形状的单个冰晶粒子光谱数据集，获得了考虑多种形状冰晶的新冰云光学性质参数化方案，与以往同类研究结果进行了比较。将包含多种形状的新冰云光学性质参数表应用于气候模式中，考察其与球形方案的区别，揭示了新方案对气候模拟的改进。在新的多形状冰云方案下，考察了不同权重比例对冰云光学性质及冰云辐射过程的影响。最后，构建了二流-四流球谐函数谱展开累加辐射传输的新方案，并在气候模式中与原有的Eddington 累加方案进行了比较，发现新方案对气候模拟会产生比较大的影响，有助于改善全球气候模式中普遍存在的赤道平流层中下层的温度冷偏差现象；同时基于新的冰云参数化方案和四流辐射传输模式，详细分析了在辐射传输算法中通常使用的HG (Henye-Greenstein)近似对冰云短波辐射传输过程的影响。