Comparison of cloud properties between cloudsat retrievals and airplane measurements in mixed-phase cloud layers of weak convective and stratus clouds

Cloud microphysical properties including liquid and ice particle number concentration (NC), liquid water content (LWC), ice water content (IWC) and effective radius (RE) were retrieved from CloudSat data for a weakly convective and a widespread stratus cloud. Within the mixed-phase cloud layers, liquid-phase fractions needed to be assumed in the data retrieval process, and one existing linear (p1) and two exponential (p2 and p3) functions, which estimate the liquid-phase fraction as a function of subfreezing temperature (from -20°C to 0°C), were tested. The retrieved NC, LWC, IWC and RE using p1 were on average larger than airplane measurements in the same cloud layer. Function p2 performed better than p1 or p3 in retrieving the NCs of cloud droplets in the convective cloud, while function p1 performed better in the stratus cloud. Function p3 performed better in LWC estimation in both convective and stratus clouds. The REs of cloud droplets calculated using the retrieved cloud droplet NC and LWC were closer to the values of in situ observations than those retrieved directly using the p1 function. The retrieved NCs of ice particles in both convective and stratus clouds, on the assumption of liquid-phase fraction during the retrieval of liquid droplet NCs, were closer to those of airplane observations than on the assumption of function p1.     

Behaviour of H2O2, NH3, and black carbon in mixed-phase clouds during CIME

We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H₂O₂, NH₃ and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H₂O₂ and NH₃ are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H₂O₂ is driven by co-condensation with water vapour onto ice crystals while NH₃ uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH₄⁺ in the ice could explain this result. Finally, it appears that the H₂O₂–SO₂ reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.     

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.     

一次西风槽过程过冷云水分布特征观测研究

过冷云水生消演变规律是云物理学和人工影响天气的重要研究领域。根据Hobbs 1974年提出的假定,利用飞机、卫星、雷达和雨量计等观测资料,对2012年9月21日河北一次西风槽天气过程进行观测研究,分析其过冷云水分布特征及演变规律。结果表明,槽前云系过冷水区宽厚并且过冷水含量较高,云滴浓度和均立方根直径较大并且均匀,冷云区厚而且没有分层,没有暖云配合;近槽云系中冷云区小粒子浓度降低但云滴直径增大,冷云区夹有干层,云系变厚出现暖云配合,冷暖云液态水含量较高,冷暖云区大粒子和降水粒子浓度和尺度增大,中尺度云团移动较快;槽后云系中云滴浓度最大,但云滴均立方根直径明显减小,过冷水区出现的高度下降、厚度很薄、过冷水含量较低,冷、暖云之间有干层,暖云对应的大粒子浓度和降水粒子浓度非常大,地面降水主要由暖云过程产生;云水(过冷水)含量峰值常出现在云内逆温层的上方;利用云粒子测量系统(PMS)资料分析过冷云水生消演变特征与卫星和雷达资料具有较高的一致性。     

利用三架飞机联合探测资料分析层积混合云催化物理效应

利用2009年4月18日三架飞机联合探测层积混合云资料,结合MICAPS再分析资料、雷达、卫星及地面台站资料等,在准确区分自然云区与催化响应区的基础上,对这次降水性层积混合云的微结构和催化物理响应进行了深入研究。结果表明:云上部(4 800 m层,距云顶1 700 m,距云底3 000 m)累积了云中大部分的过冷水,是云内发展强盛区;云上部嵌入式积云区温度低于周围层云区2℃,积云区含水量分布不均,最大值为1.5 g/m~3,标准差为0.4 g/m~3,而层云区含水量最大值和标准差分别为0.6 g/m~3和0.15 g/m~3,积云区和层云区的云滴谱峰值直径分别为25μm和15μm,云滴数浓度的量级分别为102cm-3和101cm-3。对催化云而言,此次联合探测在4 800 m层捕捉到嵌入式积云区的催化响应,人工播撒Ag I会促进该层云的消散过程,催化后1 h内云区占比由71%降至13%,云中液态含水量持续减少且趋于均匀分布,催化后10 min与20 min云中含水量的最大值分别为1.0 g/m~3和1.5 g/m~3,标准差为0.3 g/m~3和0.15 g/m~3,凇附与聚合增长为主要冰相微物理过程,云滴谱先变窄,后因H-M冰晶凇附繁生而拓宽;在云的中下层则受上层催化影响而产生旺盛云区,10 min内该层云区范围显著扩大,云滴及冰相粒子尺度均增加一倍,同时旺盛云区自上而下扩展。     

地形云人工增雨条件卫星探测反演个例分析

选取2007年6月21日陕西白于山区地形云降水过程,用极轨卫星资料反演高空间分辨率的云微物理特征.对云降水物理结构分析表明:(1)山前云区(迎风坡)云顶亮温(T)为-31℃,粒子有效半径(Re)为9μm,含有丰富过冷水,缺乏冰晶;(2)T=-20℃的低云在有高云参与的情况下,产生了较多的降水;(3)山前云区面积约400...     

Properties of cloud and precipitation over the Tibetan Plateau

The characteristics of seasonal precipitation over the Tibetan Plateau(TP) were investigated using TRMM(Tropical Rainfall Measuring Mission) precipitation data(3B43). Sensitive regions of summer precipitation interannual variation anomalies were investigated using EOF(empirical orthogonal function) analysis. Furthermore, the profiles of cloud water content(CWC) and precipitable water in different regions and seasons were analyzed using TRMM-3A12 data observed by the TRMM Microwave Imager. Good agreement was found between hydrometeors and precipitation over the eastern and southeastern TP, where water vapor is adequate, while the water vapor amount is not significant over the western and northern TP.Further analysis showed meridional and zonal anomalies of CWC centers in the ascending branch of the Hadley and Walker Circulation, especially over the south and east of the TP. The interannual variation of hydrometeors over the past decade showed a decrease over the southeastern and northwestern TP, along with a corresponding increase over other regions.     

Application of aircraft observations over Beijing in cloud microphysical property retrievals from CloudSat

Cloud microphysical property retrievals from the active microwave instrument on a satellite require the cloud droplet size distribution obtained from aircraft observations as a priori data in the iteration procedure.The cloud lognormal size distributions derived from 12 flights over Beijing,China,in 2008-09 were characterized to evaluate and improve regional CloudSat cloud water content retrievals.We present the distribution parameters of stratiform cloud droplet （diameter ＜500 tm and ＜1500 μm） and discuss the effect of large particles on distribution parameter fitting.Based on three retrieval schemes with different lognormal size distribution parameters,the vertical distribution of cloud liquid and ice water content were derived and then compared with the aircraft observations.The results showed that the liquid water content （LWC） retrievals from large particle size distributions were more consistent with the vertical distribution of cloud water content profiles derived from in situ data on 25 September 2006.We then applied two schemes with different a priori data derived from flight data to CloudSat overpasses in northern China during April-October in 2008 and 2009.The CloudSat cloud water path （CWP） retrievals were compared with Moderate Resolution Imaging Spectroradiometer （MODIS） liquid water path （LWP） data.The results indicated that considering a priori data including large particle size information can significantly improve the consistency between the CloudSat CWP and MODIS CWP.These results strongly suggest that it is necessary to consider particles with diameters greater than 50 tm in CloudSat LWC retrievals.     

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.     

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.     

Impact of the Bergeron–Findeisen process on the release of aerosol particles during the evolution of cloud ice

The paper focuses on the redistribution of aerosol particles (APs) during the artificial nucleation and subsequent growth of ice crystals in a supercooled cloud. A significant number of the supercooled cloud droplets during icing periods (seeding agents: C₃H₈, CO₂) did not freeze as was presumed prior to the experiment but instead evaporated. The net mass flux of water vapour from the evaporating droplets to the nucleating ice crystals (Bergeron–Findeisen mechanism) led to the release of residual particles that simultaneously appeared in the interstitial phase. The strong decrease of the droplet residuals confirms the nucleation of ice particles on seeding germs without natural aerosol particles serving as ice nuclei. As the number of residual particles during the seedings did not drop to zero, other processes such as heterogeneous ice nucleation, spontaneous freezing, entrainment of supercooled droplets and diffusion to the created particle-free ice germs must have contributed to the experimental findings. During the icing periods, residual mass concentrations in the condensed phase dropped by a factor of 1.1–6.7, as compared to the unperturbed supercooled cloud. As the Bergeron–Findeisen process also occurs without artificial seeding in the atmosphere, this study demonstrated that the hydrometeors in mixed-phase clouds might be much cleaner than anticipated for the simple freezing process of supercooled droplets in tropospheric mid latitude clouds.     

基于CloudSat/CALIPSO资料的我国北方2个区域云垂直分布差异研究

选用2008年1月—2014年10月的Cloud Sat/CALIPSO卫星资料,对中国北方两个4°×4°区域云垂直结构及其微物理参量进行了对比研究,区域1(114~118°E,37.5~41.5°N)和区域2(110°E~114°E,37.5~41.5°N)纬度相同经度不同。结果表明:1)区域1(E1)和区域2(E2)暖云层、混合云层和冷云层的云出现概率(Cloud Occurrence Probability,COP)差别较大。E1暖云层COP春季最大,E2则在夏、秋季达到较大值;E1混合层COP最大值出现在冬季,E2则出现在春季;2个区域冷云层COP均在春季达到最大。2)2个区域的COP高值区厚度有明显的季节性差异,E1的COP高值主要出现在夏、冬季,E2则主要出现在春、夏季。E1秋、冬季云体雷达回波最大值强于E2,但春、夏季弱于区域1。3)E2在春、秋季的液水含量、冰水含量、云滴有效半径均高于E1。     

云中积冰过程微物理参量演变规律的数值模拟

利用耦合Thompson参数化物理方案的WRF（weather research and forecasting）中尺度数值模式,对发生在2008/2009年和2009/2010年冬季恩施雷达站处三次积冰过程的边界层特征和云雾微物理量进行了模拟,并与实测结果进行了对比分析.模拟结果较好地反映了恩施雷达站上空多逆温影响的温度层结特征;云水质量浓度和云雾滴中值体积直径的模拟值与观测值的平均绝对误差分别为10-2g·m-3和3.8μm;恩施雷达站上空存在一个质量浓度为0.3g ·m-3左右的高值中心,其逐渐下移接地,给积冰过程带来充足水汽,且此时通常也有降雨出现.     

山西一次降雪云物理特征的飞机观测研究

液态水含量（Liquid Water Content,LWC）是重要的云参数,对了解云微物理过程以及在人工影响天气效果检验等方面有重要的指导意义。针对已有研究的反射率因子（Z）与LWC经验公式适用范围有限的问题,利用2018—2020年飞机观测资料,在验证中国首部机载云雷达（Ka-band Precipitation Radar,KPR）探测能力和数据可靠性的基础上,采用分档平均方案,建立了适用于降水性积层混合云的Z-LWC经验公式（ 相似文献   

邢台市大气水汽及云水变化的降水前兆分析

利用MWP967KV型地基微波辐射计及红外观测仪探测数据,对邢台市2016年发生降水前的水汽含量(IWV)、液态水含量(ILW)和云底高度变化特征进行了分析.结果表明,云底高度的持续明显下降提前约1h于IWV的明显升高,IWV的明显增加提前约1h于ILW的明显升高;IWV呈持续增加时间≥3h且IWV≥4.00cm,IL...     

多普勒天气雷达谱宽数据监测机场湍流强度的可行性初探

大气湍流是一种无序的、非确定性的大气运动,它可提高云滴碰撞效率,加速云滴增长速度,在云和降水形成及发展过程中起着十分重要的作用。本文综述了国内外近60 a来云中湍流的研究进展,重点介绍了云宏微观结构特征及云中湍流对云滴碰并增长方面取得的研究成果,以期为进一步观测研究云动力学过程、完善湍流-云微物理相互作用理论及优化云参数化方案提供重要参考。

     

2005—2015年庐山云海时间变化特征及气象条件分析

采用经验频率分布、趋势分析等统计分析方法,分析了庐山气象站2005-2015年云海时间变化特征及其与气温、相对湿度和风向风速等气象要素的关系。结果表明：（1）庐山云海平均年日数为133.73 d,最多年份为172 d（2005年）,最少年份为106 d（2012年）,云海日数呈递减趋势。（2）庐山云海适宜的气象条件为：平均气温8.7~21.0℃,最高气温12.7~24.7℃,最低气温5.7~18.6℃,相对湿度 ≥ 82%,风速1.9~4.8 m·s^-1,风向为SSE和S。和无云海时相比,有云海时气温要素整体偏高,相对湿度条件更好,风速频率分布接近。（3）在2005-2015年的云海日中,有效探空数据共1 840时次,其中500时次出现逆温,占27.2%;平均逆温层底高度为793.1 m,平均逆温层厚度为1 054.4 m,平均逆温强度为0.25℃·（100 m）^-1,均大于无云海时的逆温参数。有云海时,逆温层底高度300~2 000 m和逆温强度大于等于0.4℃·（100 m）^-1所占百分比较无云海时更大,表明有云海时逆温层底更高,逆温层更厚,逆温强度更强。     

Seasonal variation and physical properties of the cloud system over southeastern China derived from CloudSat products

Based on the National Centers for Environmental Prediction(NCEP) and Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) data and Cloud Sat products, the seasonal variations of the cloud properties, vertical occurrence frequency, and ice water content of clouds over southeastern China were investigated in this study. In the Cloud Sat data, a significant alternation in high or low cloud patterns was observed from winter to summer over southeastern China. It was found that the East Asian Summer Monsoon(EASM) circulation and its transport of moisture leads to a conditional instability, which benefits the local upward motion in summer, and thereby results in an increased amount of high cloud. The deep convective cloud centers were found to coincide well with the northward march of the EASM, while cirrus lagged slightly behind the convection center and coincided well with the outflow and meridional wind divergence of the EASM. Analysis of the radiative heating rates revealed that both the plentiful summer moisture and higher clouds are effective in destabilizing the atmosphere. Moreover, clouds heat the mid-troposphere and the cloud radiative heating is balanced by adiabatic cooling through upward motion, which causes meridional wind by the Sverdrup balance. The cloud heating–forced circulation was observed to coincide well with the EASM circulation, serving as a positive effect on EASM circulation.     

聚类分析在人工增雨效果检验中的应用

在前人研究工作的基础上，对非随机区域历史回归试验进行了改进，提出了一种新的试验方案——基于聚类的浮动对比区历史回归人工增雨效果统计检验方法（CA-FCM方法），并与浮动对比区历史回归统计检验方法（FCM方法）进行了比较。通过对河南省春季6次作业进行评估得出：由于CA—FCM方法采用了聚类分析，提高了对比区和影响区的相关系数，及引入了整层大气可降水量作为协变量，所以提高了作业区自然降水量估计值的准确性，比FCM方法有更高的效果评估效率。     

Transition from the southern mode of the mei-yu front cloud system to other leading modes

Based on normalized six-hourly black body temperature （TBB） data of three geostationary meteorological satellites,the leading modes of the mei-yu cloud system between 1998 and 2008 were extracted by the Empirical Orthogonal Function （EOF） method,and the transition processes from the first typical leading mode to other leading modes were discussed and compared.The analysis shows that,when the southern mode （EOF1） transforms to the northeastern mode （EOF3）,in the mid-troposphere,a low trough develops and moves southeastward over central and eastern China.The circulation pattern is characterized by two highs and one low in the lower troposphere.A belt of low pressure is sandwiched between the weak high over central and western China and the strong western North Pacific subtropical high （WNPSH）.Cold air moves southward along the northerly flow behind the low,and meets the warm and moist air between the WNPSH and the forepart of the low trough,which leads to continuous convection.At the same time,the central extent of the WNPSH increases while its ridge extends westward.In addition,transitions from the southern mode to the dual centers mode and the tropical-low-influenced mode were found to be atypical,and so no common points could be concluded.Furthermore,the choice of threshold value can affect the number of samples discussed.