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     

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.     

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.     

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.     

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。     

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。     

Retrieving microphysical properties and air motion of cirrus clouds based on the doppler moments method using cloud radar

Radar parameters including radar reflectivity,Doppler velocity,and Doppler spectrum width were obtained from Doppler spectrum moments.The Doppler spectrum moment is the convolution of both the particle spectrum and the mean air vertical motion.Unlike strong precipitation,the motion of particles in cirrus clouds is quite close to the air motion around them.In this study,a method of Doppler moments was developed and used to retrieve cirrus cloud microphysical properties such as the mean air vertical velocity,mass-weighted diameter,effective particle size,and ice content.Ice content values were retrieved using both the Doppler spectrum method and classic Z-IWC(radar reflectivity-ice water content) relationships;however,the former is a more reasonable method.     

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。     

山东北部一次夏末雹暴地面降水粒子谱特征

为了更好地认识雹暴等强对流降水的微物理特征,利用降水现象仪观测资料和CINRAD/SA-D双偏振天气雷达的粒子相态识别和反射率因子等产品,分析2019年8月16日出现在山东北部的一次雹暴降水的雨、冰粒子谱(包括直径2～5 mm的霰粒子和直径大于5 mm的冰雹)的识别以及雨滴谱的演变特征,结果显示:济南双偏振天气雷达0....     

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。     

Model studies on the effect of nitric acid vapour on cirrus cloud activation

The effect of elevated nitric acid concentrations on cloud particle number concentrations and sizes of mixed phase cirrus cloud (containing both supercooled liquid and frozen ice particles) is studied using a detailed multicomponent condensation model. Our model calculations suggest that high nitric acid volume mixing ratios (VMRs), corresponding to upper tropospheric measurements, can increase the ice crystal number concentrations substantially especially in the case of freezing of non-activated solution droplets (as opposed to freezing of supercooled cloud droplets). This is due to increased droplet sizes caused by nitric acid absorption and the resulting uptake of water.     

A modelling study of the effect of ice particle sizes and relative velocity on ice crystal/graupel collisional charge transfer

The effect of ice particle sizes and relative velocity on the sign of charge transfer during graupel/ice crystal interactions in thunderstorms is considered based on the concept of the Relative Growth Rate Hypothesis that the ice surface growing faster by water vapour diffusion charges positively. Diffusional growth rates of ice crystals and riming graupel particles are calculated for various particle sizes and velocities, and the sign of charging during crystal/graupel collisions is determined. The study reveals that larger graupel charges more negatively, while larger ice crystals, or higher relative velocity, lead to increased positive graupel charging.     

Impact of primary ice nucleation parameterizations on the formation and maintenance of cirrus

Different ice nucleation algorithms are implemented in a cloud microphysical scheme and numerical simulations of clouds are performed using a three-dimensional mesoscale model. The predicted ice crystal fields are found to be sensitive to the different modes of calculation of the number of deposition/ condensation freezing nuclei and contact freezing nuclei. Also a time and supercooling dependence of this sensitivity is established.The general features of the cirrus clouds observed by the research aircraft Falcon during the 1989 (International Cirrus Experiment) mission ICE212 are compared to those of the cirrus clouds generated by the model. The cloud top height, the cloud ice content and the ice number concentrations seem to be reproduced well.     

山西一次降雪云物理特征的飞机观测研究

通过飞机直接进入降雪云进行探测,并配合MICPAS（气象信息综合分析处理系统）、雷达和卫星等资料,对2011年11月29日山西一次降雪云宏、微观结构特征进行分析。研究发现:本次降雪过程的雷达回波以10～20 dBZ大片层状云回波为主,镶嵌了超过30 dBZ的块状强回波,雷达径向速度零线呈较强的“S”型弯曲,出现“牛眼”结构,从低层到高层有较强的风垂直切变。液态水含量主要位于3.2 km以下,最大值为0.0697 g m?3,N₅₀（粒子直径大于50 μm的冰雪晶数浓度）、N₂₀₀（粒子直径大于200 μm的冰雪晶数浓度）和冰水含量主要产生于层积混合降雪云的上部,极大值出现在?9.3°C附近,分别为188.4 L?1、33.5 L?1和0.121 g m?3。?14.4°C～?19.7°C冰晶图像以针状、柱状和不规则状为主,以冰晶的凝华增长为主。?9.3°C附近冰雪晶图像以辐枝状、不规则状为主,辐枝状冰晶的聚并碰撞和折裂繁生可能是造成此处冰雪晶高浓度的主要原因。利用指数形式能较好地拟合冰雪晶谱分布,谱拟合参数可以用幂函数N_os=1.021λ1.684表示（其中,N_os、λ分别表示截距和斜率,N_os越大表示小粒子数浓度越大,λ越大表示小粒子数浓度占总粒子数浓度比例越高）,相关系数R2为0.86。3.2 km以下存在三次逆温,逆温层的出现使云微物理特征量和拟合参数N_os减小,抑制了云内凇附增长和凝华增长,导致本次观测谱拟合参数N_os、λ随温度的变化规律与以往的观测不一致,逆温强度越大抑制作用越大。     

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.     

A case study of cirrus layers with variable 3.74 µm reflection properties in the first FIRE experiment, 2 November 1986

Summary Remotely sensed scanning radiometer and lidar data on cirrus clouds were obtained during the cirrus FIRE IFO experiment in November 1986 from the ER-2 aircraft plat-form.Data were examined particularly on 2 November for an area in the vicinity of Wausau, Wisconsin where unusual effects were noticed in bispectral histograms from various channels in the scanner data.After calibration of the data in spectral channels of both the Scan Cloud Radiometer (SCR) and Multichannel Cloud Radiometer (MCR) instruments, including direct comparison between compatible channels in the two instruments, it was found that the 0.856 µm SCR channel gave good data, whereas the 0.665 µm and 0.74 µm SCR channels gave large offsets, when compared with the MCR 0.754 µm data. The latter channel was found to compare well in a second comparison with coincident AVHRR channel satellite data. Similarly, the SCR 11.17 µm data gave consistent results and the SCR 3.74 µm data were carefully calibrated.Bispectral histograms formed between 0.856 µm, 3.74 µm and 11.17 µm SCR channel data indicated that some coherent layers of cirrus clouds were giving enhanced solar reflectance at 3.74 µm, indicative of small (~ <25 µm radius) particles, whereas other neighbouring layers gave little reflectance.A comparison of 0.856 µm reflections with 11.17 µm absorption optical depth indicated that the small particles where probably ice crystals. A comparison of 3.74 µm solar albedo and 11.17 µm absorption optical depths of these layers with theoretical calculations for ice spheres indicated a mode radius of about 8 µm for the cloud particle size distribution. An estimate from similar recent calculations on hexagonal ice crystals indicated that the retrieved effective radius would be increased to 25 µm. The difference between the two retrieved radii was a measure of the uncertainty in the retrievals, considering also differences in the assumed size distributions.Qualitative comparison with ER-2 lidar data gave a tentative identification of the reflecting layers.The results demonstrate the power of the 3.74 µm channel for identification of small-particle layers in cirrus.With 9 Figures     

京津冀地区夏季降水冰云和非降水冰云云特征对比分析

利用2013～2016年的Aqua MODIS卫星和CloudSat卫星的二级产品资料,对发生在京津冀地区夏季的降水冰云和非降水冰云进行了统计。基于此,对比分析了两类冰云的云类型,研究了二者在云特征参数、云层数及垂直结构上的差异,并且探究了二者在不同通道下云特征参数的相对大小。结果表明:1）京津冀地区的降水冰云以深对流云和雨层云为主,分别占48.63%和34.65%,而非降水冰云以高层云和卷云为主,分别占55.62%和31.58%。2）降水冰云和非降水冰云的平均云顶温度、云顶高度、光学厚度、积分云水总量、有效粒子半径分别为230.99 K、10.90 km、53.26、937.98 g/m2、31.45m和236.17 K、10.10 km、12.81、209.00 g/m2、27.54 μm。3）降水冰云以单层云为主,占80.39%,双层云占18.75%;而非降水冰云仍以单层云为主,占85.35%,双层云则占14.38%,比降水冰云低。4）相较于非降水冰云,降水冰云中卷云和高积云云体位置较高,而高层云和深对流云位置较低。5）随高度变化,降水冰云冰水含量是双峰结构,而非降水冰云是单峰结构;二者的粒子数浓度则差异不大;非降水冰云的粒子有效半径在5～7.5 km随高度变化不大,而降水冰云则随高度减小。6）降水冰云的积分云水总量、光学厚度和粒子有效半径>≥模态[、、分别代表该云特征参数在1.6、2.1、3.7 μm通道中的数值,当n=1, 2, 3时,分别代表光学厚度（b₁）、积分云水总量（b₂）、有效半径这三种（b₃）]的比例都高于非降水冰云,而二者在云参数≥≥模态的比例则有差异。     

Numerical simulation of the scavenging rates of ice crystals of various microphysical characteristics

Numerical models of trajectories of small aerosol spheres relative to oblate spheroids were used to determine ice crystal scavenging efficiencies. The models included the effects of aerodynamic flow about the ice particle, gravity, aerosol particle inertia and drag and electrostatic effects. Two electric configurations of the ice particle were investi-gated in detail. The first applied a net charge to the ice particle, of magnitude equal to the mean thunderstorm charge distribution, while the second applied a charge distribution, with no net charge, to the ice particle to model the electric multipole charge distribution. The results show that growing ice crystals with electric multipoles are better scavengers than single ice crystals with net thunderstorm charges, especially in the Greenfield gap (0.1 to 1.0 μm), and that larger single crystals are better scavengers than smaller single crystals. The results also show that the low density ice crystals are more effective scavengers with net charges than they are with charge distribution.     

Ice cloud microphysics,radiative transfer and large-scale cloud processes

Summary Parameterization programs for cloud microphyscs and radiative transfer involving ice clouds have been developed in terms of the mean effective size and ice water path. The mean effective size appears to be adequate in representing the ice crystal size distribution for radiative parameterizations. For a given ice water path, smaller mean effective sizes reflect more solar radiation, emit more IR radiation and enhance net radiative heating/cooling at the cloud top and bottom than larger sizes. The presence of small ice crystals may generate steeper lapse rates in clouds. A 3-D global cloud model that prescribes the horizontal wind fields in a 24 hour period is used to investigate the sensitivity of the mean effective size of ice crystals on the simulation of radiative heating, temperature, cloud cover and ice water content. A variation in the mean effective size from 75 to 50 m in a 24 hour prediction on simulation generates more cooling above the high cloud top and a decrease of temperature. These results lead to an increase of high cloud cover in some latitudes by as much as 4% and, at the same time, a decrease of middle cloud cover by 3–4% in latitudes between 60°S and 60°N.With 7 Figures     

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.