Observations and Modeling of Ice Water Content in a Mixed-Phase Cloud System

The ice water content(IWC) distribution in a mixed-phase cloud system was investigated using Cloud-Sat data,aircraft measurements,and the Weather Research and Forecasting(WRF) model.Simulated precipitation and IWC were in general agreement with rain gauge,sat-ellite,and aircraft observations.The cloud case was char-acterized by a predominant cold layer and high IWC throughout the cloud-development and precipitation stages.The CloudSat-retrieved products suggested that the IWC was distributed from 4.0 to 8.0 km,with the maximum values(up to 0.5 g m-3) at 5.0-6.0 km at the earlymature stage of cloud development.High IWC(up to 0.8 g m-3) was also detected by airborne probes at 4.2 and 3.6 km at the late-mature stage.The WRF model simulation re-vealed that the predominant riming facilitated rapid ac-cumulation of high IWC at 3.0-6.0 km.

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.

Aircraft Measurements of the Microphysical Properties of Stratiform Clouds with Embedded Convection

The presence of embedded convection in stratiform clouds strongly affects ice microphysical properties and precipitation formation.In situ aircraft measurements,including upward and downward spirals and horizontal penetrations,were performed within both embedded convective cells and stratiform regions of a mixedphase stratiform cloud system on 22 May 2017.Supercooled liquid water measurements,particle size distributions,and particle habits in different cloud regions were discussed with the intent of characterizing the riming process and determining how particle size distributions vary from convective to stratiform regions.Significant amounts of supercooled liquid water,with maxima up to 0.6 g m−3,were observed between−3℃ and−6℃ in the embedded convective cells while the peak liquid water content was generally less than 0.1 g m−3 in the stratiform regions.There are two distinct differences in particle size distributions between convective and stratiform regions.One difference is the significant shift toward larger particles from upper−15℃ to lower−10℃ in the convective region,with the maximum particle dimensions increasing from less than 6000μm to over 1 cm.The particles larger than 1 cm at−10℃ are composed of dendrites and their aggregates.The other difference is the large concentrations of small particles(25–205μm)at temperatures between−3℃ and−5℃ in the convective region,where rimed ice particles and needles coexist.Needle regions are observed from three of the five spirals,but only the cloud conditions within the convective region fit into the Hallett-Mossop criteria.

与飞机观测资料对比评估WRF微物理方案集合的模拟能力

使用WRF模式中的Morrison,WSM6,SBM,P3四种微物理方案的集合,模拟中尺度对流系统降水过程.研究发现不同的微物理方案模拟的对流云区液态含水量,冰水含量的垂直分布各不相同,而模拟的层状云区液态含水量,冰水含量的垂直分布结果相似.总的来说与其他方案相比,Morrison方案和集合平均的结果最接近观测值.我们也注意到在一些区域,所有成员均高估了液态含水量2-8倍,这也导致了在这些区域集合平均值与观测相比仍然有很大的差距.

机载毫米波雷达反演降水性积层混合云暖区液态水含量及其与飞机观测的对比

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(Z=2454.71×LWC^(1.614)),决定系数达0.995,均方根误差(RMSE)为0.2 g/m^(3)。验证表明,该经验公式反演的液态水含量与飞机实测的LWC吻合较好,且在大多数情况下都优于已有经验公式反演的结果。

大陆性积云不同发展阶段宏观和微观物理特性的飞机观测研究

2014年7月3日,山西省人工降雨防雹办公室在该省忻州地区开展了国内首次大陆性积云飞机穿云探测。本文利用机载云物理探测资料,分析研究了不同发展阶段的积云宏、微观物理特性,主要结论有:(1)初生发展阶段的积云水平尺度约为8.2 km×5.5 km(经向×纬向,下同),云厚约2 km;云中以小云粒子为主,云滴凝结增长;水平方向上,云液水含量(LWC)和粒子浓度(Nc)的最大值均位于云体中心位置;垂直方向上,云水分布相对均匀,但随着高度增加,云粒子浓度变小,粒子尺度增大;粒子谱符合伽马分布,峰值量级为102cm^-3μm^-1,谱宽在100μm以下。(2)成熟阶段的积云水平尺度约为4.6 km×10 km,云厚约4 km;云内可以观测到积冰和雨线;小云粒子浓度随高度增加起伏变化,3600 m、4100 m和4900 m高度处存在峰值;大云粒子浓度随高度先增加后减小,最大值出现云底以上1.6 km高度,云底以上1.3 km高度附近有降水粒子形成;粒子谱呈多峰分布,暖区符合伽马分布,冷区为伽马分布和M-P分布相结合,且随着高度的增加拓宽,4400 m高度以下的谱宽小于200μm。(3)消散阶段积云尺度约为11 km×5.6 km,云厚约2 km,云下有降水粒子存在。

集合预报模式与飞机观测在层状云微物理特征方面的对比研究

云中的液态含水量,冰水含量以及粒子数浓度在大气科学领域有着重要的作用。由于初边界条件的不确定性以及微物理方案的内在缺陷,云中微物理特征的准确预报仍然是一大挑战。集合预报方法是减少预报不确定性的有效途径。本文使用10个集合成员与飞机观测资料进行对比研究太行山东麓一次大范围层状云降水过程。研究结果发现:与控制预报相比,集合平均对液态含水量和冰水含量的预报能力有所提高,然而粒子数浓度的预报与观测相比存在低估,主要是因为模式低估了小于1000微米的降水粒子。