适用于云微物理特性连续变化的辐射传输新理论研究及其在气候模式模拟中的应用

In current climate models, cloud microphysical properties are often divided into several homogeneous layers in vertical direction for radiative transfer parameterization. This artificial stratification introduces discontinuities in the vertical distribution of the cloud microphysical properties, which results in the obvious bias in the radiative transfer simulations. Radiative transfer equation, which is used to describe the radiation process of continuous microphysical properties of cloud, is essentially integro-differential equation with variable coefficients. Therefore, it is difficult to solve it. Recently, the variational iteration method from nonlinear field provides a new idea for solving the radiative transfer equation with variable coefficients. This project intends to use the above method to propose a new radiation scheme to deal with the radiation of continuous cloud microphysical properties. It includes three items as follows: 1) we will develop a new four-stream theory, which will be applied to deal with the continuity of cloud microphysical properties and eventually propose a new four-stream scheme for solar radiative transfer parameterization; 2) basing on the basic theory of infrared radiative transfer, we will develop a new four-stream theory to deal with the radiation of continuous cloud microphysical properties, and eventually propose a new four-stream scheme for infrared radiative transfer parameterization; 3) the above new radiative transfer scheme will be applied to the BCC_AGCM and the evaluation will be made to estimate the simulation capability of cloud radiative properties.

现有的气候模式的辐射方案均采用对云微物理特性进行垂直均匀分层后再进行辐射传输计算，但这种方法使得模式层交界处的云微物理特性不连续，从而导致辐射传输计算产生较为明显的偏差。由于描述云微物理特性连续变化的辐射传输方程本质上是变系数的积分-微分方程，因此求解非常困难。近年来，非线性领域发展起来的变分迭代方法为求解变系数辐射传输方程提供了新的思路。本项目拟借助该方法建立一种能够适用于云微物理特性连续变化的辐射方案，并主要围绕以下三方面进行研究：1）建立适用于云微物理特性连续变化的短波四流近似辐射理论，并在此基础上，研制新的短波四流近似辐射传输方案； 2）以热红外辐射传输基本理论为基础，建立适用于云微物理特性连续变化的长波四流近似辐射理论，并研制新的长波四流近似辐射传输方案；3）将新发展的长、短波辐射传输方案耦合到国家气候中心的气候模式BCC_AGCM中，进行数值模拟，评估新方案对云辐射特性的模拟能力。

现有气候模式的辐射方案均采用对云微物理特性进行垂直均匀分层后再进行辐射传输计算，但这种方法使得模式层交界处的云微物理特性不连续，从而导致辐射传输计算产生较为明显的偏差。本项目建立了适用于云微物理特性连续变化的短波/长波四流近似辐射传输方案，以减少当前气候模式中由于忽略云光学性质随高度连续变化而引起的模拟误差；并讨论了不同辐射传输方案在模式中的精度和效率；将不同辐射方案应用到气候模式中并比较所计算的气候物理量差异；建立了红外快速辐射传输模式（ERTM），用于模拟Himawari-8卫星上搭载的成像仪（AHI）观测的亮温。