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41.
In order to improve our understanding of microphysical properties of clouds and precipitation over the Tibetan Plateau (TP), six cloud and precipitation processes with different intensities during the Third Tibetan Plateau Atmospheric Science Experiment (TIPEX-Ⅲ) from 3 July to 25 July 2014 in Naqu region of the TP are investigated by using the high-resolution mesoscale Weather Research and Forecasting (WRF) model. The results show unique properties of summertime clouds and precipitation processes over the TP. The initiation process of clouds is closely associated with strong solar radiative heating in the daytime, and summertime clouds and precipitation show an obvious diurnal variation. Generally, convective clouds would transform into stratiform clouds with an obvious bright band and often produce strong rainfall in midnight. The maximum cloud top can reach more than 15 km above sea level and the velocity of updraft ranges from 10 to 40 m s-1. The simulations show high amount of supercooled water content primarily located between 0 and -20℃ layer in all the six cases. Ice crystals mainly form above the level of -20℃ and even appear above the level of -40℃ within strong convective clouds. Rainwater mostly appears below the melting layer, indicating that its formation mainly depends on the melting process of precipitable ice particles. Snow and graupel particles have the characteristics of high content and deep vertical distribution, showing that the ice phase process is very active in the development of clouds and precipitation. The conversion and formation of hydrometeors and precipitation over the plateau exhibit obvious characteristics. Surface precipitation is mainly formed by the melting of graupel particles. Although the warm cloud microphysical process has less direct contribution to the formation of surface precipitation, it is important for the formation of supercooled raindrops, which are essential for the formation of graupel embryos through heterogeneous freezing process. The growth of graupel particles mainly relies on the riming process with supercooled cloud water and aggregation of snow particles. 相似文献
42.
Weijian WANG Zhanyu YAO Jianping GUO Chao TAN Shuo JIA Wenhui ZHAO Pei ZHANG Liangshu GAO 《Journal of Meteorological Research》2019,(3):528-539
Effects of weather modification operations on precipitation in target areas have been widely reported, but little is specifically known about the downwind (extra-area) effects in China. We estimated the extra-area effect of an operational winter (November-February) aircraft cloud-seeding project in northern Jiangxi Province in eastern China by using a revised historical target/control regression analysis method based on the precipitation data in winter. The results showed that the overall seasonal average rainfall at the downwind stations increased by 21.67%(p=0.0013). This enhancement effect was detected as far as 120 km away from the target area. Physical testing was used to compare the cloud characteristics before and after seeding on 29 November 2014. A posteriori analysis with respect to the characteristics of cloud units derived from operational weather radar data in Jiangxi was performed by tracking cloud units. Radar features in the target unit were enhanced relative to the control unit for more than two hours after the operational cloud seeding, which is indicative of the extra-area seeding effect. The findings could be used to help relieve water shortages in China. 相似文献
43.
利用不同形状冰晶的散射特性,获得了非球形冰晶云的94/220 GHz测云雷达双波长比,探讨了非球形冰晶云的双波长比与云内微物理参数的关系,分析了衰减前后的星载雷达反射率因子及双波长比的垂直廓线。结果表明:（1）双波长比可以反映小到0.1 mm中值尺度的冰粒子,对粒子总数、谱的形状参数不敏感,对粒子大小、形状、云衰减较敏感。（2）雷达灵敏度一定时,星载雷达可测云厚与雷达波长、冰含水量（IWC）的垂直分布、云厚及衰减有关;没有进行衰减订正时,双波长比和衰减有关,冰含水量越大,波长越短,衰减越大,双波长比最大值与可探测云厚有关。两部雷达可探测冰含水量为0.001—0.1 g/m3、厚2 km的冰云;当云厚5 km、冰含水量垂直分布在0.001—0.2 g/m3时,云厚的94%基本可以被220 GHz云雷达探测到。（3）如果两部雷达气象方程中用水的介电因子,测量回波强度应进行介电因子的订正后再计算双波长比。 相似文献
44.
利用常规观测资料、多普勒雷达资料以及NECP(1°×1°)逐6 h再分析资料,对2016年9月22日内蒙古河套地区强冰雹天气成因进行分析,结果表明:在前倾槽有利的天气尺度环流背景下,中高层干冷空气叠加在低层暖湿空气上形成了对流不稳定层结条件。较大的对流有效位能(CAPE)、假相当位温θse高能区、0～6 km中等强度的垂直风切变有利于强冰雹的形成。反射率因子有"钩状回波"、前侧入流缺口、后侧入流缺口;前侧入流缺口表明有上升气流,强盛的上升气流有利于空中大冰雹的增长,后侧入流缺口表明有下沉气流,有可能引起破坏性大风。基本径向速度剖面有明显的中气旋特征,强烈的辐合有利于对流风暴上升运动的进一步发展;对流风暴后侧有辐散下沉气流降落到地面,辐散风出流促使对流风暴前沿的暖湿气流强迫抬升,从而使上升运动得到进一步的加强。反射率因子剖面有弱回波区、回波悬垂且55 dBZ以上的强回波核心位置超过-20℃层等温线高度以上;弱回波区左侧的回波强度高达55～60 dBZ且已经接地,表明有大冰雹降落到地面。 相似文献
45.
为提高新疆戈壁地区云的自动化观测水平,基于全天空红外成像仪(WSIRCMS)获取的红外辐射图像,利用辐射传输模式SBDART分析了仪器测量波段对有云无云状况的敏感性并构建了拟合方程,同时利用典型季节的晴空辐射样本拟合了晴空曲线并统计形成了晴空阈值,最后利用统计晴空阈值对全天空红外辐射图像进行云像素识别和总云量计算。将不同季节总云量计算结果同人工观测结果对比验证表明：观测时段算法计算总云量和人工观测总云量差值在±2成以下的概率均在80%以上,说明该方法具有较高的准确度和较强的实用性,在观测业务中具有较好的应用前景。 相似文献
46.
为了对地基全天空红外测云仪获得的云图进行分类,该文从压缩感知理论出发,提出了一种利用云图灰度稀疏性进行云状识别的新方法。首先运用典型云图样本构造冗余字典,然后通过梯度投影 (GPSR) 算法和正交匹配 (OMP) 算法求取测试样本在冗余字典中的l1范式最优解,最后利用残差法和稀疏比例法对云状进行判别并输出。采用压缩感知理论进行云状识别,降低了对特征提取技术的要求,为云状的自动识别提供了新思路,对典型波状云、层状云、积状云、卷云和晴空的总体识别率分别达到75%,91%,70%,85%和93%,平均识别率为82.8%。 相似文献
47.
上海“7·31”局地强对流快速更新同化数值模拟研究 总被引：2，自引：0，他引：2
利用雷达、自动气象站、飞机观测(AMDAR)和探空等多种观测资料,采用中尺度数值预报模式WRF和资料同化系统ADAS,对2011年7月31日上海局地强对流过程进行了快速更新同化数值试验。结果表明,数值试验模拟降水的发生时间、落区和随时间演变与实况基本一致,较好再现了海陆热力差异导致上海南北两支海陆风爆发、形成低层辐合线,在热岛效应的叠加下进一步增强,继而引发局地强对流的过程。快速更新同化技术可有效延长此次过程的预警时效,这为城市强对流业务预报提供了新的思路。 相似文献
48.
甘肃武威市一次局地大到暴雨天气成因分析 总被引：1，自引：0，他引：1
利用常规天气图、FY-2D卫星云图、单站地面资料、NCEP再分析物理量场资料,对2013年8月6日发生在甘肃武威市对流性强降雨天气成因进行了诊断分析。结果表明:强降雨是在一定的大尺度环流背景下高低层天气系统共同作用下发生的,地面气象要素的剧烈变化是强对流天气能量的释放过程;湿度条件和水汽在本地辐合为大到暴雨提供了充沛的水汽;高层辐散、低层辐合以及强烈的上升气流是大到暴雨发生的动力条件;强烈的不稳定能量和不稳定层结是对流增强、雨强较大的必要条件;对流云团的发展和加强是降雨强度较大的直接原因。 相似文献
49.
利用毫米波测云雷达反演层状云中过冷水 总被引：1，自引：0，他引：1
毫米波测云雷达已成为研究云内微物理参数的有效工具,利用其从混合相云中识别出过冷水,对人工影响天气及预防飞机积冰具有重要意义,对我国毫米波雷达的数据处理也具有借鉴作用。本文利用英国的35 GHz、94 GHz测云雷达,结合激光雷达和探空资料,采用阈值法,反演分析了层状云中的过冷水。结果表明:(1)毫米波雷达联合激光雷达可以识别层状云中的过冷水,其结果与微波辐射计测量的液态水路径或毫米波雷达的双峰谱相符合;(2)利用多普勒速度的双峰谱可以反演混合相云中的过冷水含量、冰晶含水量。混合相云的雷达反射率因子主要取决于冰晶,根据雷达反射率因子反演会低估云内液态水含量;(3)本次层状云降水的亮带以上含有较多过冷水,此处35 GHz的雷达回波强度随冰晶的增大而减弱,且冰晶的含水量主导了总液态水含量。 相似文献
50.
A large area of unrealized precipitation is produced with the standard convective parameterization scheme in a high-resolution model, while subgrid-scale convection that cannot be explicitly resolved is omitted without convective parameterization. A modified version of the convection scheme with limited mass flux at cloud base is introduced into a south-China regional high-resolution model to alleviate these problems. A strong convection case and a weak convection case are selected to analyze the influence of limited cloud-base mass flux on precipitation forecast. The sensitivity of different limitation on mass flux at cloud base is also discussed. It is found that using instability energy closure for Simplified Arakawa- Schubert Scheme will produce better precipitation forecast than the primary closure based on quasi-equilibrium assumption. The influence of the convection scheme is dependent on the upper limit of mass flux at cloud base. The total rain amount is not so sensitive to the limitation of mass flux in the strong convection case as in the weak one. From the comparison of two different methods for limiting the cloud-base mass flux, it is found that shutting down the cumulus parameterization scheme completely when the cloud-base mass flux exceeds a given limitation is more suitable for the forecast of precipitation. 相似文献