三维辐射传输模式分析非均匀云对天空辐射场影响

为了解非均匀分立云体分布状况下的天空辐射场与无云晴空辐射场的差异, 本文借助一个三维辐射传输数值模式SHDOM模拟了离散云块分布条件下的天空辐射场分布, 重点分析不同云况分布情况下“非云”大气的辐射分布特征, 并将该区域与无云晴空大气辐射场的相同区域进行了比对。工作主要从辐亮度以及450 nm/650 nm的辐射比两参数入手进行讨论。研究发现, 相对无云晴空大气, 云的存在会对周围“非云”大气散射辐射产生影响, 影响程度与云量、云及气溶胶光学厚度等参数相关。数值模拟结果表明, 在云量不太大的条件下, 无云视场空间的大部分辐射值与无云晴空相比变化很小, 集中在±2％之间。这一结果表明, 已有的一维均匀大气辐射传输模式运算结果所得云与非云相元的判据基本适用于非均匀分布的有云大气。另一方面, 模拟结果表明我们也完全可以利用非均匀有云大气中的无云视场观测结果进行大气气溶胶等晴空大气光学特征的探测研究。     

云三维结构对加热率廓线及通量影响的模拟

大气加热率强度与结构是驱动全球大气环流的关键因素,实际加热率分布与云三维结构密切相关。作者使用三维蒙特卡洛辐射传输模式,模拟计算了云分辨模式所得3个典型三维云场的加热率廓线及通量;定义了两个参数来同时描述加热率廓线的垂直分布和强度,通过与独立像素近似算法对比,定量统计分析了高分辨率下云三维结构对辐射的影响。结果表明,在高分辨率条件下云三维结构对加热率廓线和通量影响十分显著,且不同结构云场所体现的影响各具特点,提出需要考察现有大气模式中云三维结构对当前所用加热率计算方案的订正方向。     

飑线型降水云微波辐射特性的数值研究

本文将三维云的微物理模式的输出作为三维辐射传输模式的输入，对降水云的微波上行辐射率同地球物理参数间的关系进行了初步研究。在侧边界条件不对称的情况下，如果不考虑实际存在的云间相互辐射作用而模拟降水云的上行辐射率时，模拟出的亮温在低频段将低估卫星上测到的亮温值；在高频段则依降水云上层含冰量的大小而异，即在降水云上层含冰量小的区域，将低估星上测到的亮温，且低估的幅度较低频通道的大，而在降水云上层含冰量大的区域，可能高估星上测到的亮温，但高估的幅度较小。     

三维有云大气辐射变温率数值模拟研究——邻云辐射效应

大气数值模式普遍采用一维辐射传输模型,无法表征有云大气中的三维辐射传输过程,从而影响数值模拟乃至数值天气预报的准确性。为评估这种不确定性,研究了水平云体间的三维辐射相互作用及其改变云体热力结构的规律,力求为改进数值模式辐射计算方案提供理论依据。选取I3RC PhaseⅡ的典型积云场和层积云场作为试验对象,将云场中心区域云体视为目标云体,周围云体为邻近云体,采用宽带三维辐射传输模式SHDOM模拟长波和短波辐射变温率的空间分布,定量阐明邻近云体对目标云体热力结构的影响。结果表明,邻云在长波区域对目标云体主要起辐射保温的作用,目标云体增温区域集中于邻云一侧的云体表面层,增温强度与云覆盖率和云间距离倒数成正比,最高可达3.08K/h,云体增温的厚度与目标云体液态水含量成反比;在短波区域,邻云同时起散射增温和遮蔽降温的作用,太阳垂直入射时,散射增温效应较弱,变温率空间差异小;当太阳天顶角增大后,遮蔽降温效应逐步起主导作用,造成目标云体被邻云遮挡一侧的表面层明显降温,峰值可达-1.72K/h,数值上甚至超过邻云长波增温效应。总之,邻近云体可以明显改变目标云体的变温率空间分布,引入三维邻云辐射效应对改进大气数值模式辐射计算方案具有重要意义。     

使用物理方法反演中国陆地雨强和水凝物垂直结构

使用MM5模式模拟了11个降水个例,获得中国陆地的降水廓线,由蒙特卡罗辐射传输模式计算其上行辐射亮温,构成初始云一辐射数据库.采用对照表方法从中获得Db_ml和Db_m2两个数据集,作为GPROF反演算法的先验数据集.对2007年7月的3次强降水过程的地面雨强进行反演,与微波成像仪(TMI)及NESDIS、GSCAT、...     

陆面模拟中植被辐射传输参数化方案研究

在冠层二流辐射传输模式基础上新发展了一个描述太阳短波辐射在植被中传输的冠层四流辐射传输模式.冠层四流辐射传输模式是在大气辐射传输理论的基础上得到一组描述短波辐射在植被中传输过程的冠层辐射传输基本方程,引进大气中求解辐射传输方程的四流近似解法,并求得冠层四流辐射传输方程的解析解.方程中各项参量能够反映叶子或冠层特殊的几何和光学特征.冠层向上、向下辐射通量取决于冠层散射相函数、叶子在入射光方向投影面积、单个叶子反射率和透射率、叶面积指数以及直射光入射太阳高度角等.四流模式计算叶子水平倾角时对太阳短波辐射的反照率,与二流模式结果比较可以验证模式的理论推导和建模都是正确的:计算结果的比较,表明四流模式在水平叶角分布时计算的冠层反照率与二流模式结果一致,同时直射光从任何太阳高度角入射的冠层反照率结果也一致,从而证明发展的冠层四流辐射传输模式是成功的.模拟试验中将两种模型同时耦合到同一个陆面过程模式中进行比较试验,结果表明,冠层四流辐射传输模式能够得到更精确的植被反照率,从而使得陆面模式计算的地表吸收的净太阳辐射通量更接近于观测值.     

块状云的辐射性质及其对大气辐射收支的影响

本文利用三维辐射传输方程讨论了块状云阵的辐射性质，考虑了云块之间对太阳辐射的遮挡作用， 相互的辐射交换，及地面和大气辐射的影响。计算了云阵的反射率α，长波辐射通量F，有效云量Ne及云灵敏度因子δ随云量的变化，并与平面平行云模式作了比较。结果表明:平面平行云模式在云量小时给出的Δα/ΔN偏大，ΔF/ΔN偏小，因而δ偏大；在云量大时给出的Δα/ΔN偏小，ΔF/ΔN偏大，δ偏小。高原地区短波Δα/ΔN比平原地区大。双层云出现时Δα/ΔN及δ均变小。     

IAP AGCM中短波辐射方案的改进研究Ⅰ.引入Fu-Liou短波辐射方案

冰云和水云对短波辐射性质(消光系数、单次散射反照率及不对称因子)的影响很不相同,应分别计算.Fu-Liou短波辐射方案(以下称Fu-Liou code)就是对冰云和水云分别采用了不同的参数化方案,云的短波辐射性质直接由云的物理性质来确定.因此,Fu-Liou code在云的处理方面物理意义更清晰且很合理.作者将Fu-Liou code引入IAP AGCM-Ⅱ中,称为Version 2.对当代气候场的模拟结果表明,Version2的各个物理过程是协调匹配的,且其对气候场的模拟性能是好的,从而为进一步改进IAP AGCM的短波辐射方案提供了很好的模式基础.       

一个三维Monte-Carlo地气耦合辐射传输模式

建立了一个可靠和较高计算效率的三维Monte-Carlo地气耦合辐射传输模式(3DMC).该模式在光子释放和定位、地气耦合、辐射率高分辨模拟计算和计算效率等方面有所发展.     

IAP AGCM中短波辐射方案的改进研究I·引入Fu-Liou短波辐射方案

冰云和水云对短波辐射性质(消光系数、单次散射反照率及不对称因子)的影响很不相同,应分别计算。Fu-Liou短波辐射方案(以下称Fu-Liou code)就是对冰云和水云分别采用了不同的参数化方案,云的短波辐射性质直接由云的物理性质来确定。因此,Fu-Liou code在云的处理方面物理意义更清晰且很合理。作者将Fu-Liou code引入IAP AGCM-II中,称为Version 2。对当代气候场的模拟结果表明,Version 2的各个物理过程是协调匹配的,且其对气候场的模拟性能是好的,从而为进一步改进IAP AGCM的短波辐射方案提供了很好的模式基础。     

层状云微物理参数反演及其辐射效应的个例研究

利用毫米波云雷达、微波辐射计联合反演方法,对2015年11月11日安徽寿县的一次层状云过程的云参数进行了反演,将所得云参数加入到SBDART辐射传输模式中,进行辐射通量计算,并将计算的地面辐射通量与观测的地面辐射通量进行了对比分析。研究表明:1)利用毫米波雷达和微波辐射计数据联合反演的云参数比较可靠;2)利用SBDART模式并结合反演的云参数,可以准确实时地计算地面及其他高度层的长短波辐射通量;3)在反演的云参数中,光学厚度对地面各种辐射通量的影响是最大的,云层的光学厚度越大,到达地面的太阳短波辐射越小,地面反射短波辐射也越小。另外云底温度越高,云体向下发射的红外长波辐射越大。地面向上的长波辐射是地面温度的普朗克函数,随地面温度而变;4)云对地面的短波辐射强迫为负值,对地面有降温的作用。云对地面的长波辐射强迫是一个正值,对地面有一个增温的作用;5)云对地面的净辐射强迫随时间变化很大,它的正负与太阳高度角和云参数有关。     

Calculating the Climatology and Anomalies of Surface Cloud Radiative Effect Using Cloud Property Histograms and Cloud Radiative Kernels

Cloud radiative kernels (CRK) built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere (TOA) fluxes, and it is expected that the CRKs would also be useful in the analyses of surface radiative fluxes, which determines the regional surface temperature change and variability. In this study, CRKs at the surface and TOA were built using the Rapid Radiative Transfer Model (RRTM). Longwave cloud radiative effect (CRE) at the surface is primarily driven by cloud base properties, while TOA CRE is primarily decided by cloud top properties. For this reason, the standard version of surface CRK is a function of latitude, longitude, month, cloud optical thickness (τ) and cloud base pressure (CBP), and the TOA CRK is a function of latitude, longitude, month, τ and cloud top pressure (CTP). Considering that the cloud property histograms provided by climate models are functions of CTP instead of CBP at present, the surface CRKs on CBP-τ histograms were converted to CTP-τ fields using the statistical relationship between CTP, CBP and τ obtained from collocated CloudSat and MODIS observations. For both climate model outputs and satellites observations, the climatology of surface CRE and cloud-induced surface radiative anomalies calculated with the surface CRKs and cloud property histograms are well correlated with those calculated from surface radiative fluxes. The cloud-induced surface radiative anomalies reproduced by surface CRKs and MODIS cloud property histograms are not affected by spurious trends that appear in Clouds and the Earth's Radiant Energy System (CERES) surface irradiances products.     

Analysis of Short-term Cloud Feedback in East Asia Using Cloud Radiative Kernels

Cloud radiative kernels were built by BCC_RAD(Beijing Climate Center radiative transfer model) radiative transfer code. Then, short-term cloud feedback and its mechanisms in East Asia(0.5°S-60.5°N, 69.5°-150.5°E) were analyzed quantitatively using the kernels combined with MODIS satellite data from July 2002 to June 2018. According to the surface and monsoon types, four subregions in East Asia—the Tibetan Plateau, northwest, temperate monsoon(TM), and subtropical monsoon(SM)—were selected. The average longwave, shortwave, and net cloud feedbacks in East Asia are-0.68 ± 1.20, 1.34 ± 1.08, and 0.66 ± 0.40 W m~(-2) K~(-1)(±2σ), respectively, among which the net feedback is dominated by the positive shortwave feedback. Positive feedback in SM is the strongest of all subregions, mainly due to the contributions of nimbostratus and stratus. In East Asia, short-term feedback in spring is primarily caused by marine stratus in SM, in summer is primarily driven by deep convective cloud in TM, in autumn is mainly caused by land nimbostratus in SM, and in winter is mainly driven by land stratus in SM. Cloud feedback in East Asia is chiefly driven by decreases in mid-level and low cloud fraction owing to the changes in relative humidity, and a decrease in low cloud optical thickness due to the changes in cloud water content.     

一维辐射对流模式对云-辐射强迫的数值模拟研究

利用一维辐射－对流气候模式, 详细研究了云量、云光学厚度以及云高等要素的变化对大气顶和地面太阳短波辐射和红外长波辐射通量以及云的辐射强迫的影响, 给出了计算这些物理量的经验拟合公式。结果表明, 云具有极为重要的辐射－气候效应。云量、云光学厚度以及云高即使只有百分之几的变化, 所带来的辐射强迫也可以与大气二氧化碳浓度加倍所产生的辐射强迫（3.75 W/m2）相比拟。例如, 当分别给它们+3%的扰动时, 即取云量变化0.015, 云光学厚度变化0.27, 以及云高变化0.15 km时（在实际的地球大气中, 这种尺度的变化是完全可能发生的）, 那么,可以得到地气系统的太阳短波辐射强迫-3.10 W/m2以及红外长波辐射强迫-1.77 W/m2, 二者之和为-4.78 W/m2, 已经完全可以抵消大气二氧化碳浓度加倍所产生的辐射强迫。但是, 当云量、云光学厚度以及云高向相反方向产生类似扰动时, 所产生的辐射强迫可能极大地放大二氧化碳浓度增加所产生的增强温室效应。因此, 研究结果揭示出, 不管是为了解释过去的气候变化, 还是预测未来的气候变化, 亟待加强在一个变化了的气候环境（例如地面温度升高）下, 云将发生何种变化的研究。     

A finite element–spherical harmonics model for radiative transfer in inhomogeneous clouds: Part I. The EVENT model

We present a new numerical radiative transfer model for application to solar radiation transport in three-dimensional (3D) cloudy atmospheres. The code uses the finite element–spherical harmonics (FE–P_N) approximation to solve the second-order even-parity form of the transport equation. It is validated by comparison with solutions from two well-established, deterministic radiative transfer models, the one-dimensional (1D) DISORT code and the spherical harmonics discrete ordinates method (SHDOM). The cases solved show generally good agreement, but also reveal some differences. EVEn-parity Neutral particle Transport (EVENT) is very efficient at performing 1D calculations quickly and, even for quite high angular resolutions, is faster. EVENT also has a competitive speed for the simpler, less-heterogeneous multidimensional cases but it is slower than SHDOM for more variable cases. However, there is significant potential to improve the performance of EVENT; it has not yet been optimised for speed and, as such, is not a finished product. Even as it is, EVENT could be used to produce fast, lower-resolution estimates for applications where this would be sufficient, or at lower-spatial resolutions with partial homogenisation.Another difference between the models is that the SHDOM algorithm is designed for small-scale inhomogeneous cloud fields in which the grid spacing is comparable to the mean free path. Problems arise from the use of larger grid cell optical depths, with an increase in the number of iterations required and a lack of flux conservation. Neither of the models is specifically constrained to conserve flux, but the conservation of flux gives an indication of the accuracy of the solution. Increasing the spatial and angular resolution can improve the accuracy but this is not always possible for very large 3D scenes. The grid-point method of property definition in SHDOM means that it performs best for cases with a continuous variation in extinction as this avoids discontinuities in the source function. The finite clouds used in our tests have sharp boundaries that are easily defined in EVENT but the difficulties caused by these in SHDOM are evident in excesses of up to 10 fluxes.The EVENT mesh resolution is determined by the local optical depth; it has no problem in dense areas but has more trouble in coping with voids or optically thin regions. These conditions are easily handled in SHDOM through streaming of photons along discrete ordinates but EVENT must implement methods such as a ray-tracing algorithm. Cases with extreme values of the extinction coefficient are probably best avoided with EVENT, but slightly larger-scale cases with greater optical depths, not suitable for SHDOM, may be solved more easily. These factors should be considered when selecting the most appropriate method for a particular application.     

不同侧边界条件下水平有限降水云的微波辐射模式研究

从空间微波遥感降水定量分布的目标出发，本文研究在非对称侧边界条件下水平有限降水云的微波辐射率的计算公式。由普适性三维辐射传输方程出发，推导出非对称横向边界条件下的微波辐射率解析表达式。用热带降水云典型参数所作初步数值试验表明，相对于对称侧边界条件非对称侧边界条件对于上行（卫星所测）辐射率具有不可忽略的作用，且这种作用对于不同的微波频率具有不同的强度，甚至有符号的差别。云的不均匀尺度越小，这种作用越强。由于热带降水大多具有高度非均匀对流云带状或云团结构，本文所发展的模式将对微波遥感这类降雨定量分布发挥重要作     

SBDART辐射传输模式及其在飞机潜在积冰区反演中的应用

SBDART(平面平行辐射传输模式)是近年来国际上比较流行的一种计算辐射传输的模式，该模式旨在解决在卫星遥感和大气辐射能量平衡研究中遇到的各种辐射传输问题。它是基于大量经过仔细筛选的物理模式而建立起来的辐射传输模式，并且在实践中发展完善。文章详细介绍了SBDART模式的功能和结构，并利用SBDART模式结合卫星资料反演出云的光学厚度、有效粒子半径及消光系数，实现了对飞机积冰区域的有效识别。