The coalescence of water drops II. The coalescence problem and coalescence efficiency     

Nitza Arbel  Zev Levin 《Pure and Applied Geophysics》1977,115(4):895-914

By the use of the model of approaching drops (Arbel and Levin, 1977) the coalescence efficiencies of drops are computed. It is found that for interactions of drops at their terminal velocities the coalescence depends both on the size of the large drop and on the size ratio of the interacting drops in agreement with the experimental results of Whelpdale and List (1971) and Levin and Machnes (1977).The results were found to be sensitive to the assumption of the drops deformation and to the critical separation distance. This distance is defined as the distance at which the drops begin to merge. The variations of the coalescence efficiency with these parameters is discussed.Appendix: List of symbols D distance between the deformed surfaces of the drops - D _o initial value ofD - D _s stop distance, the distance at which the impact velocity vanishes - D _c critical coalescence distance - E collection efficiency - E ₁ collision efficiency - E ₂ coalescence efficiency - E _2R coalescence efficiency for collisions with stationary targets - F _c centrifugal force - p ratio of the radii of the interacting drops - r _o initial distance between drops' centers - R _L radius of larger drop - R _s radius of smaller drop - R _D radius of deformation - v approach velocity of two deformed surfaces - v _o initial value ofv - V _i impact velocity (given negative sign when drops approach each other) - V _c critical impact velocity - W _i velocity of the smaller drop at infinity for it to reachD _o with velocityv _o - x _i impact distance, the distance between the trajectories of the two drops - x _c critical impact distance for coalescence -  average critical impact distance for coalescence - X _c critical impact distance for collisions - coefficient of deformation given in equation 1 - _i impact angle defined byWhelpdale andList (1971) given also inArbel andLevin (1977) - coefficient of deformation given in equation 2 - viscosity of air - _i impact angle used inArbel andLevin (1977) and here - _c critical angle for coalescence - average critical angle for coalescence On sabbatical leave (1976–77) from the Department of Geophysics and Planetary Sciences, Tel Aviv University, Ramat Aviv, Israel.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Research Status and Progress of Balloon-borne Cloud and Precipitation Particles Probe     

Peng Wang  Lei Liu  Xichuan Liu  Shuai Hu  Shijun Zhao  Wenming Ji  Taichang Gao 《地球科学进展》1986,35(7):704-714

The accurate observation of the microphysical structure of cloud and precipitation plays an important role in understanding the formation of clouds and precipitation. In-situ measurement using measuring instruments carried by meteorological balloons is an effective way to obtain the microphysical properties of cloud and precipitation particles, which is a supplementary means for aircraft to observe cloud and precipitation particles. This observation method plays a more and more important role in in-situ measurement. According to the difference of the working principle of the existing balloon-borne cloud and precipitation particles probes, the detectors can be divided into particle impact-sampling sensors, particle imaging sensors, light-scattering sensors, light intensity attenuation sensors and charge measurement sensors. The working principles, key technologies and main advantages and disadvantages of typical instruments were summarized, and their applications to detailed cloud structure acquisition, cloud remote sensing method establishment, cloud and precipitation physical process research and parameterization, and scientific observation of thunderstorm clouds were briefly introduced. Finally, the development trend of balloon-borne cloud precipitation particle detectors was prospected, which will provide reference for related technical research and equipment development.  相似文献   

甘肃省春季沙尘暴强弱年份大气环流特征对比分析   总被引：4，自引：0，他引：4  

俞亚勋  赵建华 《干旱气象》2003,21(3):48-57

文中使用NCEP/NCAR1955～2000年全球月平均再分析网格点资料(2.5°×2.5°纬度/经度)和甘肃省区域性沙尘暴过程资料,分别选取了甘肃省5个春季典型沙尘暴年份和5个春季非沙尘暴年份,对其气候平均的大尺度环流场和有关物理量场的动力和热力结构差异进行了对比分析。初步探讨了甘肃省春季沙尘暴发生与全球海温异常的关系。分析结果表明,甘肃省春季沙尘暴年和非沙尘暴年大尺度高低空环流场和有关物理量场差异明显,从而揭示了沙尘暴形成的大尺度环流以及动力和热力因子影响的事实,以期对我国西北地区沙尘暴气候成因有更全面深入的了解,为沙尘暴短期气候预测提供理论依据和强信号。  相似文献   

海盐气溶胶和硫酸盐气溶胶在云微物理过程中的作用   总被引：14，自引：2，他引：14       下载免费PDF全文

赵春生  彭大勇段英 《应用气象学报》2005,16(4):417-425

利用大气气溶胶和云分档模式研究海盐气溶胶和硫酸盐气溶胶在云微物理过程中的作用, 计算结果表明:云中液态水含量随高度的分布并不随海盐、硫酸盐的数目以及云团上升速度的变化而变化; 随着云滴数目的增加, 云滴的有效半径会减小; 硫酸盐对云滴数目影响起主导作用, 海盐在水汽相对充足情况下增加了云滴数目, 在水汽相对不足的情况下减少了云滴数目; 硫酸盐粒子浓度特别强的情况下 (人类活动污染比较严重时), 如果水汽相对不足, 云滴数目会明显小于硫酸盐粒子浓度; 而海盐粒子的存在, 加剧了水汽的供应不足, 从而可以在很大程度上进一步降低云滴数目。也就是说, 在有些情况下, 如果不考虑海盐气溶胶的作用, 硫酸盐气溶胶对云特性的影响会被过高估计。  相似文献   

西北地区空中云水资源的时空分布特征   总被引：12，自引：6，他引：12  

陈勇航  黄建平  陈长和  张强  冯建东  金宏春  王天河 《高原气象》2005,24(6):905-912

利用1983年7月至1998年12月国际卫星云气候计划ISCCP D2的月平均云资料,对西北地区空中云水资源的时空分布特征进行了系统的研究。结果表明:三个不同区域的月平均总云量、光学厚度和云水路径的区域平均值分别在52.5%~58.3%,2.6~6.6和44.9~77.6 g.m-2之间;西北地区空中云水资源多年平均分布有其沿地形分布的特点,总云量、中云量、总光学厚度和总云水路径的高值区均在天山、昆仑山、祁连山一带,而低值中心一般分布在塔里木盆地—内蒙古西部戈壁沙漠—黄土高原西北部一带。此外,祁连山、青海所在的高原气候区云水资源近年呈上升趋势,特别是总光学厚度和总云水路径15年来呈明显上升趋势,分别约上升了0.8和16.4 g.m-2。  相似文献   

近20年全球总云量变化趋势分析   总被引：29，自引：2，他引：29       下载免费PDF全文

丁守国赵春生  石广玉武春爱 《应用气象学报》2005,16(5):670-677

利用ISCCP月平均云气候资料集的总云量资料, 采用趋势分析的方法, 得到1983年7月至2001年9月近20年来全球平均总云量的变化趋势, 并分析云量变化的可能原因。近20年全球增温幅度加快, 研究这期间云的变化, 对气候研究和模拟具有重要的意义。结果表明:平均大气环流决定总云量的分布;全球平均总云量的变化趋势在20世纪80年代末发生逆转, 即由增加转为减少;全球平均云量呈减少的变化趋势, 2000年与1987年相比, 减少量约占平均总云量的4%;从地理位置上看, 云量的变化存在区域性差异, 热带和中纬度地区的总云量减少较多, 高纬度地区云量略有增加, 其中南极大陆云量增加较多。  相似文献   

MODIS多光谱云相态识别技术的应用研究   总被引：1，自引：1，他引：1       下载免费PDF全文

周著华白洁  刘健文纪飞  齐琳琳李玮 《应用气象学报》2005,16(5):678-684

介绍了卫星多光谱云相态识别的基本原理, 并给出了EOS/ MODIS云相态识别的流程。针对简单和复杂云场, 利用个例并结合无线电探空资料与MODI S三通道合成图肯定了多光谱云相态识别的合理性和实际效果。文中对几个特定天气系统(西南涡旋和西太平洋台风)下大面积云场相态分析的结果表明:多光谱云相态识别技术有一定应用价值, 且需要引入可见光技术来减少红外谱段对多层云覆盖和薄卷云的相态分析误差。  相似文献   

西北地区不同类型云的时空分布及其与降水的关系   总被引：15，自引：3，他引：15       下载免费PDF全文

陈勇航黄建平  王天河金宏春 葛觐铭 《应用气象学报》2005,16(6):717-727

利用1983年7月～2001年9月国际卫星云气候计划ISCCP D2的月平均资料，对西北不同区域不同类型云的云量和云水路径的时空分布及其与降水的关系进行了研究。结果表明:高原气候区是各种云出现最多的地区，特别是积状云的云量明显高于其他两区，但这些云的云水路径值低；西北地区大多数云云量的高值区出现在天山山区、北疆地区、陕西东南部和青藏高原的部分地区。高云和部分中云云量空间分布特征与降水有着较好的一致性:沿着天山—昆仑山—祁连山一带以及陕南和／或陇南地区是高值区，低值区在塔里木盆地—内蒙古西部戈壁沙漠—黄土高原西北部一带；绝大多数云类春夏季节云量维持较高，秋冬季节云量较少。云水路径值较大的层状云类的云量多寡与降水多寡相一致；积状云类和层积云类云量多少与降水没有一定的关系，在降水偏少时，这类云的云量大多与降水正常时相近，有些云的云量甚至比降水偏多时还要多。  相似文献   

Is the spring water responsible for the fossilization of faunal remains at Florisbad, South Africa?     

Rod M. Douglas 《Quaternary Research》2006,65(1):87-95

It is has been suggested that faunal remains at Florisbad were fossilized in a spring context due to the mineralized spring water. However, the environment conducive to the precipitation of CaCO₃ and other authigenic minerals was formed largely through the salinization of the organic layers and clay, and the mineralization of the groundwater. Factors contributing to this favorable environment include: CaCO₃ saturation, pH, the decomposition of halophytes, Eh, rainfall, biomineralization, and aeolian deposition. With the exception of pH, none of the above factors feature in a spring context, with evidence suggesting that the spring water may historically never have carried sufficient minerals for fossilization, and that contact with the spring water may actually have resulted in the demineralization of previously fossilized material. In light of this evidence, it is concluded that the fossilization of faunal remains at Florisbad took place in a sedimentary organic matter and clay environment and could not have taken place in the spring vents where there is an undersaturation of Ca.  相似文献   

Water wars in the Middle East: a looming threat     

Hussein A. Amery 《The Geographical journal》2002,168(4):313-323

This paper explains how hydropolitical dynamics and spatial variables almost triggered a water war between Israel and Lebanon because the latter was building a pump on the Wazzani Spring, a tributary of the Jordan River. The convergence of a regional drought, history of violent confrontations between the two riparians, distrust, varying development needs and territorial disputes almost culminated in a war between these east Mediterranean neighbours. While most international water disputes in the Middle East will be resolved peacefully, some are likely to trigger violent confrontations threatening political stability in the Middle East in the next few decades.  相似文献