ICE Particle Size and Shape Effect on Solar Energy Scattering Angular Distribution

The rare occurrence of te halos produced by cirrus ice crystals in nature has been investigated by modelling the incident solar (visible) light scattering angular distribution using the Monte Carlo/ray tracing method.The results show that the irregular shapes of ice crystals and large population of small ice particles in cirrus are responsible forthe rare occurrence of halos.     

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。     

冰—水球形粒子在太阳短波段的吸收与衰减

根据Mie理论以及Aden和Kerker的理论,分别计算了纯水、纯冰和冰—水分层同心球在可见光和近红外波段的吸收、散射与衰减截面。结果表明,对于同样尺度大小的粒子,表面融化冰球或冰外壳包水球的单次散射特征值与纯冰纯水球的相比在整个太阳辐射短波段都相差不大,这是因为在此波段范围内冰和水的复折射指数的实部和虚部都很接近。此结果基本排除了0℃层附近表面融化冰晶粒子在太阳波段可能产生强吸收带,从而可以解释（部分的）云吸收异常现象这一想法。另一方面,在整层云吸收计算中,相对水含量可能较小但尺度较大的冰晶粒子的吸收是     

Effects of horizontal orientation on the radiative properties of ice clouds

Transfer of radiation through cirrus consisting of non-sphericalice crystals randomly oriented in a plane (2D model) is solved by using the discrete-ordinates method. The model is employed to determine the radiative flux properties and the intensity distribution of cirrus for both solar and thermal infrared ra-diation. Comparison of the 2D cloud model with the conventional 3D cloud model, i.e., randomly oriented in a three- dimensional space, shows that the preferential orientation of ice crystals has a substantial effect on the cloud solar albedo. The difference in the cloud albedo computed from the two models can be as large as 8% for a cirrus of 2 km thickness. On the thermal infrared side, although the flux emission for cirrus is less affected by the orientation of ice crystals, the difference in the upward radiance using 2D and 3D models is also significant.     

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     

Single scattering from frozen hydrometeors at microwave frequencies

Scattering of electromagnetic waves from homogeneous or coated spheres can be computed in a mathematically exact way using the Mie theory. Therefore, for many approaches in remote sensing, frozen hydrometeors are parameterized as ice spheres. However, many frozen hydrometeors have non-spherical overall shapes and lack a spherically symmetric internal structure. They exist in a huge variety of shapes and exhibit different mixtures of ice, water and air. Therefore it is desirable to accurately compute scattering from non-spherical particles in order to clearly understand the effect the shape of a hydrometeor has on its scattering pattern.In this study, single scattering parameters like scattering cross section, absorption cross section, and asymmetry factor were calculated for frozen hydrometeors using the Discrete Dipole Approximation (DDA). The particles were modeled as hexagonal plates, columns, needles and dendrites by applying known dimensional relationships. The calculations were carried out over a wide range of centimeter and millimeter-wavelengths (1 GHz to 300 GHz), since millimeter-wave radiometers are highly sensitive to scattering by frozen hydrometeors in the atmosphere.The study results show that for size parameters < 1 (a ratio between wavelength and particle size) the scattering cross section of randomly orientated ice crystals is close to that of an equal volume ice sphere. Absorption cross section and asymmetry factor of non-spherical particles however are up to twice as high as that of equal volume ice spheres. Further the influence of the assumed model for the refractive index of ice at microwave wavelengths on the scattering parameters is investigated.     

光吸收对冰晶粒子散射相函数的影响

本文利用射线跟踪法对冰晶粒子散射、吸收进行了研究。从理论上对一些常见的近似处理方法进行了讨论，计算了长为300μm，半径为30μm的六棱柱状冰晶粒子在不同波段的光散射相函数以及在波长2.2μm时，五种不同大小冰晶粒子的单次散射反照率。结果表明，即使在有吸收情况下，Snell公式和Lambert公式仍是近似成立的，而吸收效应对散射相函数有明显影响。     

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.     

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。     

Optical properties of cirrus transition zones over China detected by CALIOP

A transition zone near cirrus lateral boundaries can be detected by CALIOP (cloud–aerosol lidar with orthogonal polarization). In the present study, for such transition zones over China, a number of optical properties, such as the backscatter coefficient and depolarization ratio, showed transitional characteristics between cirrus and clear sky. The stepped horizontal profile showed sharp changes in particle number and morphology between cirrus clouds and clear sky. The color ratio, however, was unable to show cirrus transition features because of the low signal-to-noise ratio. Typical ice particles presented a color ratio of 0.55–1.25 and a depolarization ratio of greater than 0.12, which were significantly higher than those of clear sky. Therefore, optical properties in transition took the form of stepwise horizontal profiles. The proportion of typical-featured particles also demonstrated a stepped horizontal profile similar to the optical characteristics, but the relationship between the proportion and the optical characteristics was not uniform in the cirrus clouds, transition zone, and clear sky. Therefore, the optical changes in the transition zone were caused by not only the change in particle concentration, but also the change in the particles themselves. The probability density distribution of the transition-zone widths showed a positive skewness distribution, and transition zones with widths of 3–5 km occurred most frequently. Overall, transition-zone width decreased with increasing temperature and increased with increasing vertical and horizontal wind speeds. This trend demonstrated independence with the direction of the vertical and horizontal winds. These observations implied that the transitional features were caused by material exchange, such as entrainment and turbulent transport, near the cirrus lateral boundaries, and by the phase transformation of particles, such as sublimation.     

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。      

用红外和水汽两个通道的卫星测值指定云迹风的高度

提出了一种改进的用红外和水汽两个通道的测值指定云迹风高度的算法。利用红外水汽散点图和云迹风本身自动地将有低云的目标区、有半透明卷云的目标区、有密蔽高云的目标区分开。在有低云的目标区和有密蔽高云的目标区用红外一个通道指定云高。在有半透明卷云的目标区用红外和水汽两个通道指定云高。在用两个通道的测值指定云高时，假定卷云高度以上不存在水汽，以红外和水汽两个通道亮温相同这个方程与两个通道辐射测值线性相关的方程联立解出云的高度     

利用卫星云图估算黄河中游地区平均面雨量

介绍了利用卫星云图资料估算黄河中游面雨量的基本方法：将GMS卫星1h间隔的可风和红外云图作为判别的两个特性进行分类，确定红外光线资料的所有最小值点作为对流核；多参照Negri-Adler的方法，应用斜率参数消除卷云；应用－维云模式确定红外线图上对流核的降水率，层状云降水通过一个温度阈值给出。另外，通过2001年7月26日至28日黄河流域出现的一次较强降雨过程进行应用分析，得出结论－－利用卫星云图估算黄河中游地区平均雨量的方法具有很好的实用价值。     

近红外波段凝结核性质对雨滴散射特性的影响

用M ie散射理论,在已知大气气溶胶粒子的折射率基础上,计算并讨论大气气溶胶以及在其上凝结形成的雨滴的散射相函数、散射效率因子等散射特性。结果表明,对流层中气溶胶粒子的散射能力依次为水滴,冰晶,海洋性粒子,沙尘性粒子,水溶性粒子,煤烟。对于在可溶性核上凝结形成的雨滴,海洋性核的散射能力强于水溶性核的散射能力。由不可溶性核凝结形成雨滴的散射能力依次为煤烟核、冰晶核和沙尘性核。纯水雨滴的散射能力介于沙尘性核和冰晶核之间,强于海洋性核。该结论可以为光学测雨仪器在不同地区条件下的参数设置提供依据。     

热带深对流云砧数值模拟及云凝结核数浓度对其影响的初步试验

利用中国科学院大气物理研究所发展的三维强风暴模式，对Egrett Microphysics Experiment with Radiation Lidar and Dynamics（EMERALD）试验期间的一次长寿命热带深对流个例进行对流产生、发展、消亡过程以及云砧的数值模拟，并与实测资料［包括C波段双线偏振雷达图像资料、机载云粒子成像仪（CPI）探测的云砧卷云微物理特性以及激光雷达探测的云砧宏观特性资料］进行了细致的对比，然后通过改变模式中最大云滴数浓度进行有关云凝结核数浓度影响云砧卷云冰晶含水量和数浓度的敏感性试验。模式较好地模拟出系统的一些重要宏观特征，如爆发性增长阶段、各高度雷达水平反射率因子的最大值、对流云主体移动方向、云砧底部和顶部高度。对云砧冰相粒子含水量、数浓度以及平均直径等微观特征的模拟结果与实测也比较接近。对于本文个例而言，异质核化为冰晶形成的最主要方式，其次为过冷云滴的均质核化。敏感性试验结果表明:当云凝结核数浓度增加时，爆发性增长阶段的垂直速度减小，使得对流云从中低层向高层的水物质输送量减少，从而使云砧卷云冰晶的数量减少。     

Average ice crystal size and bulk short-wave single-scattering properties of cirrus clouds

The bulk single-scattering properties of cirrus clouds required for driving the radiation scheme in large-scale climate models are computed with respect to various size distributions and ice crystal shapes. It is shown that the average ice crystal size, defined as the ratio of total volume to the total projected area, can well-characterize the effect of various size distributions in determining the bulk radiative properties of cirrus clouds. Details of the size distributions are not significant in specifying the radiative properties of these clouds if the effective average size is thus defined. Therefore, the ratio of the total volume to the total projected area is an ideal parameter for describing the bulk single-scattering properties. The effect of ice crystal shape is not critical in the parameterization of the extinction coefficient and single-scattering albedo. However, the various crystal habits must be accounted for in the parameterization of the asymmetry parameter. The resulting parameterization is intended for radiative transfer calculations involving cirrus clouds in large-scale models.     

基于CloudSat卫星资料分析东太平洋台风的云、降水和热力结构特征

利用2006～2010年的CloudSat热带气旋过境数据集资料,依据风速大小划分为不同演变阶段,对各阶段内东太平洋台风的云、降水和热力结构进行综合分析。结果表明:雷达反射率在5 km高度上下的分布截然相反,沿径向回波强度和顶高不断减小。各类云沿径向和垂直方向的分布差异较大,而深对流云的垂直尺度和发生概率始终较大。有效粒子半径、分布宽度参数和冰水含量随高度减小而粒子数浓度却增大,沿径向各冰云参数以及降雨率都不断减小。各阶段降雨率总体上夏季大于秋季,沿纬向各季节在不同阶段的分布各异。内核区降雨率近似服从指数分布且对暖的海面温度SST较为敏感,其与雷达反射率的散点分布集中在三个区域内。内核区5～10 km高度存在暖核结构,其下方恰好对应湿心区,而10 km以上相对湿度距平较大值区对应台风顶部的卷云罩。各阶段4.5 km以上为对流性稳定层结而该高度以下的层结特性各异,此外假相当位温沿径向不断减小。     

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。     

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。     

Determination of cirrus radiative parameters from combination between active and passive remote sensing measurements during FRENCH/DIRAC 2001

In the context of the next AQUA Train satellite experiment, airborne measurements were carried out to simulate satellite measurements. They were conducted between September 25 and October 12, 2001, off the coast of southern France over the Atlantic Ocean and over the Mediterranean Sea, respectively. During the intensive Field Radiation Experiment on Natural Cirrus and High-level clouds (FRENCH/DIRAC 2001), natural ice clouds were sampled from in situ and remote sensing measurements. On October 5 and 7, 2001, cirrus cloud decks were described by a complete data set acquired by: (i) in situ microphysical instruments onboard the TBM-700 aircraft: PMS probe, and Polar Nephelometer (ii) and downward-looking radiative instruments onboard the Mystère 20 aircraft: an infrared radiometer, a lidar, a visible imager with polarisation capabilities, and a middle infrared radiometer. Moreover, classical thermodynamical measurements were carried out onboard the Mystère 20. Mean microphysical characteristics of cirrus deck are derived from interpretation of remote sensing measurements. These properties are compared with those derived from in situ microphysical measurements in order to evaluate the radiative impact of natural cirrus clouds.