冰云短波辐射特性参数化

该文对卷云和高层云分别构造了15种冰晶尺度分布，3种云高和云厚，总共30种冰水含量、90种冰水程长模式。对尺度小于与大于30 μm的冰晶粒子的单次散射特性分别用表面积等效冰球Mie理论和射线光学理论进行计算。采用delta-Eddington法计算了在4种不同地面反射率下冰云的多重散射辐射传输特性，提出了冰云辐射特性的参数化公式，指出参数化公式可以用于气候模式或大气环流模式。     

Ice microphysics and climatic temperature feedback

The potential effects of ice microphysics involving ice crystal size distribution and ice water path (IWP) on climatic temperature perturbations are investigated by using a one-dimensional radiative-turbulent climate model. We define a mean effective size, denoting the width of ice crystals weighted by the geometric cross section area, to represent ice crystal size distribution. Based on aircraft measurements, both the mean effective size and IWP are related to temperature and may be parameterized as functions of temperature. The radiative properties of cirrus clouds are further parameterized in terms of these two basic cloud physics parameters. Using CO₂ doubling as the radiative forcing, feedbacks among temperature, the mean effective size and IWP, and the radiative properties of clouds are analyzed from the model results. We show that overall, a positive feedback associated with ice microphysics and the coupled radiative transfer is produced by temperature increase.     

Satellite remote sensing of the optical depth and mean crystal size of thin cirrus and contrails

Summary Crystal size and optical depth of optically thin cirrus clouds and contrails over the North Sea and Adriatic Sea on the 18^th of October 1989 are retrieved by comparison of NOAA AVHRR/2 brightness temperatures of channel 4 (9.97 µm–11.56 µm) and channel 5 (11.075 µm–12.76 µm) with one dimensional radiative transfer calculations. Measured brightness temperatures in all three infrared channels and their differences show higher values for contrails than for cirrus. The radiative properties of young contrails are consistent only, if smaller crystal size than those given for natural cirrus are adopted for the calculations. However, there is a continuous transition in radiative parameters between clouds classified as natural cirrus or contrails. For the test areas ice clouds are classified with respect to optical depth and mean crystal size. Finally infrared fluxes and heating rates in the spectral range 4 µm–40 µm are calculated for an atmosphere with a 500 m thick contrail or cirrus uncinus. At given ice content a far stronger atmospheric warming is found for a contrail with relatively small ice crystals: up to 80 K/day at cloud base for an ice content of 0.05 gm^–3 compared to 10 K/day for a cirrus uncinus with large crystals.With 11 Figures     

Correlations between microphysical properties of large-scale semi-transparent cirrus and the state of the atmosphere

By making use of TOVS Path-B satellite retrievals and ECMWF reanalyses, correlations between bulk microphysical properties of large-scale semi-transparent cirrus (visible optical thickness between 0.7 and 3.8) and thermodynamic and dynamic properties of the surrounding atmosphere have been studied on a global scale. These clouds constitute about half of all high clouds. The global averages (from 60°N to 60°S) of mean ice crystal diameter, D_e, and ice water path (IWP) of these clouds are 55 μm and 30 g m⁻², respectively. IWP of these cirrus is slightly increasing with cloud-top temperature, whereas D_e of cold cirrus does not depend on this parameter. Correlations between D_e and IWp of large-scale cirrus seem to be different in the midlatitudes and in the tropics. However, we observe in general stronger correlations between D_e and IWP and atmospheric humidity and winds deduced from the ECMWF reanalyses: D_e and IWP increase both with increasing atmospheric water vapour. There is also a good distinction between different dynamical situations: In humid situations, IWP is on average about 10 gm⁻² larger in regions with strong large-scale vertical updraft only that in regions with strong large-scale horizontal winds only, whereas the mean D_e of cold large-scale cirrus decreases by about 10 μm if both strong large-scale updraft and horizontal winds are present.     

Cirrus cloud horizontal and vertical inhomogeneity effects in a GCM

Summary A set of the inhomogeneity factor for high-level clouds derived from the ISCCP D1 dataset averaged over a five-year period has been incorporated in the UCLA atmospheric GCM to investigate the effect of cirrus cloud inhomogeneity on climate simulation. The inclusion of this inhomogeneous factor improves the global mean planetary albedo by about 4% simulated from the model. It also produces changes in solar fluxes and OLRs associated with changes in cloud fields, revealing that the cloud inhomogeneity not only affects cloud albedo directly, but also modifies cloud and radiation fields. The corresponding difference in the geographic distribution of precipitation is as large as 7 mm day⁻¹. Using the climatology cloud inhomogeneity factor also produces a warmer troposphere related to changes in the cloudiness and the corresponding radiative heating, which, to some extent, corrects the cold bias in the UCLA AGCM. The region around 14 km, however, is cooler associated with increase in the reflected solar flux that leads to a warmer region above. An interactive parameterization for mean effective ice crystal size based on ice water content and temperature has also been developed and incorporated in the UCLA AGCM. The inclusion of the new parameterization produces substantial differences in the zonal mean temperature and the geographic distribution of precipitation, radiative fluxes, and cloud cover with respect to the control run. The vertical distribution of ice crystal size appears to be an important factor controlling the radiative heating rate and the consequence of circulation patterns, and hence must be included in the cloud-radiation parameterization in climate models to account for realistic cloud processes in the atmosphere.     

On the radiative properties of ice clouds: Light scattering,remote sensing,and radiation parameterization

Presented is a review of the radiative properties of ice clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the singlescattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed.With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared(IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed.The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models(GCMs). The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate studies is proven.     

CloudSat/CALIPSO卫星资料分析云的全球分布及其季节变化特征

全球气候模式（GCM）中云的参数化方案具有不确定性,了解云的时、空变化能为参数化方案提供有效参考。利用搭载在属于A-Train卫星序列的CloudSat和CALIPSO上的94 GHz云廓线雷达（CPR）以及正交极化云-气溶胶激光雷达（CALIOP）联合的2级云分类产品,分析了2007年3月-2010年2月8种云类及三相态的云量地理分布、纬向垂直分布的季节变化特征以及云层分布概率。结果发现,卷云的分布体系与深对流云相似,主要集中在西太平洋暖池、全球各季风区及赤道辐合带,分布格局与气压带、风带季节性移动一致。层云与层积云主要分布在中低纬度非季风区以及中高纬度的洋面上。高积云与高层云的分布形成明显的海陆差异,雨层云与积云的分布形成明显的纬度差异。冰云分布与卷云相似,云高随纬度递增而递减;水云分布与层积云相似,平均分布于2 km高度;混合云集中于高纬度地区及赤道辐合带,中纬度地区随纬度变化集中于海拔0-10 km的弧形带。层状云多以多层云形式出现,积状云多以单、双层云的形式出现,层状云的云重叠现象比积状云更显著。积状和层状云的分布特征与积云和层云降水的分布特征基本一致,验证了不同类型降水的卫星观测结果,同时为气候模式的云量诊断方案提供对比验证的数据。      

Two-moment bulk stratiform cloud microphysics in the grid-point atmospheric model of IAP LASG (GAMIL)

A two-moment bulk stratiform microphysics scheme, including recently developed physically-based droplet activation/ice nucleation parameterizations has been implemented into the Grid-point Atmospheric Model of IAP LASG (GAMIL) as an effort to enhance the model’s capability to simulate aerosol indirect effects. Unlike the previous one-moment cloud microphysics scheme, the new scheme produces a reasonable representation of cloud particle size and number concentration. This scheme captures the observed spatial variations in cloud droplet number concentrations. Simulated ice crystal number concentrations in cirrus clouds qualitatively agree with in situ observations. The longwave and shortwave cloud forcings are in better agreement with observations. Sensitivity tests show that the column cloud droplet number concentrations calculated from two different droplet activation parameterizations are similar. However, ice crystal number concentration in mixed-phased clouds is sensitive to different heterogeneous ice nucleation formulations. The simulation with high ice crystal number concentration in mixed-phase clouds has less liquid water path and weaker cloud forcing. Furthermore, ice crystal number concentration in cirrus clouds is sensitive to different ice nucleation parameterizations. Sensitivity tests also suggest that the impact of pre-existing ice crystals on homogeneous freezing in old clouds should be taken into account.     

1960年以来东亚季风区云-降水微物理的直接观测研究

云-降水的直接观测结果是云微物理参数化的重要依据。自1960年以来,处于东亚季风影响下的中国实施了大量对云-降水微物理参数的观测和研究,旨在加深对云-降水微物理过程的认识,从而改进数值模式中云微物理参数化方案和指导人工影响天气作业。云-降水微物理参数包括气溶胶、冰核、云滴、雨滴、冰晶、雪晶、冰雹等粒子浓度和谱分布,以及云滴、雨滴含水量等。中国已有云-降水微物理参数的成果可归纳为:(1)通常云-降水微物理粒子浓度变化较大,但总体变化有一定的范围;(2)采用Γ函数拟合云滴谱更接近实际谱,但不同拟合谱参数差异较大;(3)可用指数函数和Γ函数来拟合层状云降水雨滴谱,Γ函数拟合积云和层积混合云降水雨滴谱精度更高;(4)中国冰核浓度较高,冰核浓度随温度的降低近似成指数变化;(5)冰晶谱、雪晶谱、冰雹谱通常采用指数函数来描述;(6)通常使用荣格(Junge)和Γ函数来分段描述气溶胶粒子谱拟合误差更小。由于云-降水过程及其反馈作用描述不准确是数值模式预报结果不确定性的最大因素,中国正在不断地推进云降水的微物理观测研究,以期进一步加深对东亚季风区云-降水微物理特征的认识,从而为模式中微物理参数化方案的改进提供观测依据和科学指导。基于数值预报模式中云微物理过程参数化发展的需要,总结了中国1960年以来云-降水微物理直接观测的研究成果,可为东亚地区云-降水微物理研究及其模式参数化方案的改进提供观测依据。此外,针对云微物理参化发展的需求,结合过去已有的大量观测提出了几点建议,为今后云-降水物理综合性观测方案的设计提供参考。     

Parameterization of the shortwave radiative properties of water clouds for use in GCMs

Summary The influence of the micro- and macrophysics of water clouds on the scattering and radiative properties of clouds is investigated using versatile cloud drop size distributions (DSDs) and Mie theory for single scattering and the delta-Eddington approximation for multiple scattering. A new parameterization scheme for the shortwave radiative properties of water clouds is presented. As for single- scattering properties, a new parameterization for cloud optical thickness () is proposed. This is based upon the seperation of the dependence of on the total number of DSDs, the cloud thickness, and the liquid water content, combined with equivalent radius. The cloud bulk radiative properties, i.e., the flux reflectance, transmittance, and absorptance, are uniquely fitted by a dimensionless parameter (X) or the optical thickness. The parameterization is compared with other schemes. Finally, the features and potential use of the scheme are discussed.With 5 Figures     

Optical properties of a vertically inhomogeneous mid-latitude mid-level mixed-phase altocumulus in the infrared region

A vertically inhomogeneous mid-latitude mixed-phase altocumulus cloud was observed around 17:26 UTC on Oct. 14, 2001 during the 9th Cloud Layer Experiment (CLEX9). In this study the microphysical and optical properties of this cloud are investigated on the basis of in-situ observed vertical profiles of particle size and habit distributions. Two cloud models, assuming that the cloud properties were vertically homogeneous and inhomogeneous, are adopted to derive the bulk optical and radiative properties of this cloud. The observed microphysical properties are combined with the theoretical solutions to the scattering and absorption properties of individual cloud particles to determine the bulk optical properties at various heights within the cloud layer. The single-scattering properties of spherical liquid water droplets and nonspherical ice crystals are obtained from the Lorenz–Mie theory and an existing database, respectively. The bulk microphysical and optical properties associated with the inhomogeneous model depend strongly on the height above the cloud-base whereas the dependence is smoothed out in the case of the homogeneous model. Furthermore, the transfer of infrared radiation is simulated in conjunction with the two cloud models. It is shown that the brightness temperatures at the top of the atmosphere in the case of the homogeneous model can be 1.5% (3.8 K) higher than their counterpart associated with the inhomogeneous cloud model. This result demonstrates that the effect of the vertical inhomogeneity of a mixed-phase cloud on its radiative properties is not negligible.     

冰晶性质对卷云辐射特征影响的模拟研究

介绍了SBDART辐射模式和libRadtran程序包，并利用这两个模式模拟分析了当卷云内冰晶性质如有效半径、冰晶含量以及形状变化时，卷云反照率的变化。模拟分析表明，在相同条件下，不同形状冰晶构成的卷云反照率有所不同，同种冰晶构成的卷云在不同波长的反照率也不同。总的来说，不论是由何种形状冰晶构成的卷云，随着卷云内冰晶含量增大，有效半径减小，卷云反照率增大。这些工作将有助于增进对lib Radtran程序包和卷云性质的了解。     

Sensitivity Study of Anthropogenic Aerosol Indirect Forcing through Cirrus Clouds with CAM5 Using Three Ice Nucleation Parameterizations

Quantifying the radiative forcing due to aerosol–cloud interactions especially through cirrus clouds remains challenging because of our limited understanding of aerosol and cloud processes. In this study, we investigate the anthropogenic aerosol indirect forcing (AIF) through cirrus clouds using the Community Atmosphere Model version 5 (CAM5) with a state-of-the-art treatment of ice nucleation. We adopt a new approach to isolate anthropogenic AIF through cirrus clouds in which ice nucleation parameterization is driven by prescribed pre-industrial (PI) and presentday (PD) aerosols, respectively. Sensitivities of anthropogenic ice AIF (i.e., anthropogenic AIF through cirrus clouds) to different ice nucleation parameterizations, homogeneous freezing occurrence, and uncertainties in the cloud microphysics scheme are investigated. Results of sensitivity experiments show that the change (PD minus PI) in global annual mean longwave cloud forcing (i.e., longwave anthropogenic ice AIF) ranges from 0.14 to 0.35 W m^–2, the change in global annual mean shortwave cloud forcing (i.e., shortwave anthropogenic ice AIF) from–0.47 to–0.20 W m^–2, and the change in net cloud forcing from–0.12 to 0.05 W m^–2. Our results suggest that different ice nucleation parameterizations are an important factor for the large uncertainty of anthropogenic ice AIF. Furthermore, improved understanding of the spatial and temporal occurrence characteristics of homogeneous freezing events and the mean states of cirrus cloud properties are also important for constraining anthropogenic ice AIF.     

不同环境温度下冰云粒子的单次散射参量

本文提出了直接Stokes参量变换的射线追踪方案,优化了作者过去建立的求解六角冰晶粒子散射的射线追踪模式.在冰晶有吸收(折射指数为复数)的情况下,新模式采用了有效折射指数处理粒子内的非单色折射波.其次,新模式还引入了有效单次散射参量,消除了来自几何透射线的前向δ散射效应.最后,根据不同环境温度下的冰云中冰晶粒子的粒径谱分布,本文计算了粒径谱积分平均的3D随机取向六角冰晶粒子的单次散射参量.文中给出的冰晶粒子单次散射参量的数值,对研究冰云辐射特性将有一定参考价值.     

从紫外到中红外谱区冰的光学常数与温度关系的研究

本文简要地讨论了冰的结构及其光学特性,并应用经典的极化理论研究了冰的光学常数与频谱和温度的关系,计算了从紫外到中红外谱区、在地球大气温度范围内冰的光学常数。对计算结果的分析表明,在高空卷云的散射和辐射传输的理论计算中,温度对云中冰晶光学常数的影响必须考虑。     

Characterization of cloud microphysical properties in different cloud types over East Asia based on CloudSat/CALIPSO satellite products

利用CloudSat/CALIPSO卫星资料,本文揭示了东亚三个代表性区域的云微物理属性,为评估和改进模式云微物理过程提供重要的观测基础.研究的云微物理量包括云水/冰质量,数浓度和有效半径.研究表明:暖云中云水质量和数浓度随高度增加而减小,有效半径处于8-14μm范围.对于冰云,云冰质量和有效半径随高度增加而减小,而数浓度在垂直方向上变化不大.此外,云微物理属性在不同云型之间存在显著差异:积云的云水质量和数浓度最大,而卷云的云水质量和数浓度最小.从三个区域的对比结果来看,相比于华东和西北太平洋地区,青藏高原地区暖云的云水质量和数浓度较小,而冰云的则较大.     

Particle size truncation effect on the inference of effective particle diameter

The effective ice crystal particle diameter (De) of cirrus clouds can be inferred by comparing the measured radar / lidar backscattering ratio with the theoretically calculated one. The calculated ratios are based upon assump-tions of ice crystal particle density and size distribution, and it will be affected by the artificially assumed particle size ranges. This size truncation effect on the inference of effective particle diameter will be investigated theoretically by assuming the cirrus ice particle spherical and particle density of 0.9g / cm3. Results show that the truncation at large particle end has very small effect on the inference of De , but the truncation at the small particle end will have some ef-fect on the inference of De.     

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。     

基于CloudSat资料对中国低纬度陆地区域卷云物理特征的研究

利用2008年9月—2016年8月的CloudSat卫星资料对发生在我国低纬度陆地区域(5°~36.5°N,78°~124°E)的卷云物理特征进行统计分析,并分别讨论东部沿海、中部、西部3个子区域的卷云物理特征的季节变化。结果表明:卷云的整层发生率西部地区整体低于中部与东部沿海地区。3个子区域整层发生率均在夏季最高、冬季最低。卷云的主要发生高度在5.04~18.71 km,垂直分布中卷云发生率的最大值出现在春季中部地区,为15.34%,高度为9.83 km。冰水路径最大值出现在夏季的东部沿海,液水路径最大值在秋季的西部地区。冰水含量、冰粒数浓度、冰粒有效半径的主要分布高度与卷云的发生高度一致,液水含量、液滴数浓度、液滴有效半径的主要分布高度在5.04~9.35 km。3个子区域卷云冰水含量、冰粒数浓度、冰粒有效半径垂直分布中大多集中在中上部;液水含量垂直分布主要集中在分布高度的中下部。四季卷云雷达反射率因子的最大值在-19.89~-16.78 dBZ,分布高度在7.19~10.55 km。     

Cirrus Cloud Macrophysical and Optical Properties over North China from CALIOP Measurements

Two years of mid-latitude cirrus cloud macrophysical and optical properties over North China are described from Earth-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) satellite measurements. Global cloud climatological studies based on active remote sensing data sets benefit from more accurate resolution of vertical structure and more reliable detection of optically thin layers.The mean values for cirrus cases over North China are 0.19±0.18 for infrared emittance,0.41±0.68 for visible optical depth, 0.26±0.12 for integrated depolarization ratio,and 0.72±0.22 for integrated color ratio.When studied using reasonable assumptions for the relationship between extinction and ice crystal backscatter coefficients,our results show that most of the cirrus clouds profiled using the 0.532μm channel data stream correspond with an optical depth of less than 1.0.The dependence of cirrus cloud properties on cirrus cloud mid-cloud temperature and geometry thickness are generally similar to the results derived from the ground-based lidar, which are mainly impacted by the adiabatic process on the ice cloud content.However,the differences in macrophysical parameter variability indicate the limits of spaceborne-lidar and dissimilarities in regional climate variability and the nature and source of cloud nuclei in different geographical regions.