J2云微物理特征-冷云微特征ppt课件

1、J2 云微物理特征-冷云微观特征,1,建议书目杨军等. 云降水物理学. 北京: 气象出版社, 2011.黄美元和徐华英. 云和降水物理. 北京: 科学出版社,1999.,2,3,冷云的定义,目前有两种定义 第一种：一块云如果铅直伸展到0层以上高度，这种云就称为冷云（见华莱士和霍布斯，2003） 第二种：有冰相过程参与的云称为冷云。（黄美元和徐华英，1999） 实际运用时，大多用第二种定义。本课程采用第二种,虽然个人建议取消暖云、冷云这两个概念，直接用水云、混合云、冰晶云这些概念。,4,为何研究冷云的微观特征？ 冰相对降水、辐射有重要影响。所以研究冷云的微观特征，有助于理解和改进天气和气候模式中

2、的云微物理过程处理方案，从而提高降水数值预报的准确性，提高气候变化模拟研究结果的可信度。,5,在水质量一定的条件下，混合相云中的冰越多，则云通 过反射太阳辐射对地面的冷却作用越弱。 这是因为冰云的光学厚度比过冷水云的小。 全球气候模拟结果表明，相比于通常所假定的-35的 冰化温度，取0作为冰化温度时全球辐射平衡将改变 17Wm-2。,冰相对辐射的影响,6,冷云的微观特征包括,冷云中的冰相粒子形状是怎样的呢? 有多大?有多少? 质量密度如何?落速如何? 专业一点的说法是: 微观特征主要关注-形状、尺度谱分布、尺度、数浓度、密度、下降末速度。,7,本章内容,形状 尺度及尺度谱分布 数浓度 密度 下

3、降末速度。,8,These pictures show real snow crystals that fell to earth in Northern Ontario, Alaska, Vermont, the Michigan Upper Peninsula, and the Sierra Nevada mountains of California. They were captured by Kenneth G. Libbrecht using a specially designed snowflake photomicroscope.,雪晶图片欣赏,9,地面观测冰晶形状的代表人物

4、,Wilson Bentley,The first substantial collection of snow crystal photographs was created by Wilson Bentley (1865-1931). A Vermont farmer, Bentley made snowflake photography his life-long passion, eventually capturing some 5000 images on old-style photographic plates. His efforts eventually came to t

5、he attention of W. J. Humphreys of the U.S. Weather Bureau, who worked with Bentley to publish nearly 2000 photographs in 1931, just before Bentleys death 1. The publication of this book, entitled Snow Crystals, introduced the world to the beauty, complexity, and diversity of snow crystals.,10,Ukich

6、iro Nakaya,中谷宇吉郎（Nakaya Ukichiro）(1900-1962)，日本物理学家。 1931年开始雪花在显微镜下拍照、人工雪的研究。不久制成与天然雪具有同一结晶的人工雪。 他将气温和水蒸汽的过饱和度画成图形，从而区分出各结晶形状的生成领域(见1941年他发表的论文雪的结晶与生长条件之关系)。,11,William Wergin,William Wergin has developed techniques for taking snow crystal photographs using an electron microscope, which is capable o

7、f examining very fine details in their structure. A number of these images can be seen at the Electron Microscopy Unit Snow Page.,12,Kenneth G. Libbrecht,/atomic/snowcrystals/,Snow crystals were captured by Kenneth G. Libbrecht using a specially designed snowflake photomicro

8、scope.,13,冰相粒子的形状分类,1951年，国际冰雪委员会根据形态提出了固态降水物的国际分类，将冰雪晶分为片状、辐枝状、柱状、针状、空间辐枝状、帽柱状、不规则晶、霰、冰粒、冰雹10种,见B. Mason, in The Physics of Clouds (Oxford University Press, 1971),14,冰相粒子的形状分类,Nakayas Classification，,see U. Nakaya, Snow Crystals: Natural and Artificial (Harvard University Press, 1954).,Physicist Uk

9、ichiro Nakaya (1900-1962) created the first systematic classification scheme for snowflakes, in which he subdivided falling snow into 41 individual morphological types,15,第三种分类,Nakaya拓展版 The most complex classification scheme is an extension of Nakayas table, published by meteorologists C. Magono an

10、d C. W. Lee in 1966 . This table includes 80 different snow crystal types. see C. Magono and C. W. Lee, Meteorological Classification of Natural Snow Crystals, Journal of the Faculty of Science, Hokkaido University, 1966.,16,冰的晶格基本形状,If you look closely at falling snow, you can see a great many diff

11、erent crystal shapes. 但是, 在地球大气温压范围内，冰的晶格基本形状是对称的六棱柱状，即有2个底面和6个侧面。为什么？水分子固态时，六角点格排列。,17,冰相粒子形状与生长环境,在冰晶的生长过程中，底面、侧面或棱边具有生长优势时将分别形成柱状、片状或辐枝状这三种最基本的冰晶形状。实际形状非常复杂，为研究方便进行了形状定义。 随着环境温度、湿度的不同及其在生长过程中的变化，造成冰晶不同部位生长速率的差异，从而形成各种形状的冰雪晶。,18,形状与生长环境的实验室研究,早期研究 温度高于-30度, 利用对流云室或非对流扩散云室, 冰晶在rabbit fur or filamen

12、ts of plastic or glass上生长. 发现 habit transitions that occur between 0度 and -18C (plates to columns to plates)首先取决于温度,其次才是过饱和度 Nakaya (1954), Kobayashi(1957), and Hallett and Mason (1958),19,第二阶段,Rottner and Vali (1974), Kumai (1982), and Pruppacher and Klett (1997)利用不同的核化方法，研究了冰晶的生长。 肯定了在0到-20C范围内的基本

13、形状，但在更低温度时结果相当不同，通常与最初的研究结果以及外场观测结果不同。,20,第三阶段,Bailey and Hallett （2002，2004）考虑了低温时气压的变化，认为气压影响水汽的扩散。Crystals were grown on clean glass filaments 结果表明，many of the earlier results were heavily influenced by the nucleation method, crystal concentration and supersaturation control (or lack of ),21,22,2

14、3,为何是这样的？能给出微观解释吗？能被自然云中的观测结果证实吗？,24,云中观测研究-仪器,25,early study,Slide Impactors 撞击取样器,26,27,28,29,Other Impactors,30,31,32,33,34,35,36,37,38,39,40,41,Results,42,43,44,45,46,47,48,本章内容,形状 尺度及尺度谱分布 数浓度 密度 下降末速度。,49,尺度的定义,50,51,52,尺度譜分布的定义,53,54,Um and McFarquhar(2009),55,56,冰相粒子PSDs函数拟合,PSDs用gamma分布来拟合：

15、 未知量的物理意义： ：截距 ：斜率 ：形状因子,57,58,Andrew J. Heymsfield,et al.Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitating Clouds: Results from In Situ Observations in TRMM Field campaigns. JAS,2002,59,本章内容,形状 尺度及尺度谱分布 数浓度 密度 下降末速度。,60,冰相粒子数浓度,61

16、,本章内容,形状 尺度及尺度谱分布 数浓度 密度 下降末速度。,62,63,本章内容,形状 尺度及尺度谱分布 数浓度 密度 下降末速度,64,下落末速度,65,66,67,68,Ice Crystal Shape. Ice crystal habits (shapes) and related properties are marked by significant uncertainty. Westbrook et al. 2008, Sulia and Harrington 2011, and several others found that the nonsphericity of ice crystals during diffusional growth may substantially affect ice-liquid partitioning in numerical models of mixed-phase stratocumulus clouds. Indeed, the shape of ice crystals strongly influences their diffusional growth rates. Also, when ice crystal sediments, they a regimes, c