冰雪晶碰并勾连增长的实验与观测分析

黄庚; 苏正军; 关立友; 张纪淮

冰雪晶碰并勾连增长的实验与观测分析

1.
中国气象科学研究院中国气象局云雾物理重点开放实验室, 北京 100081
2.
南京信息工程大学, 南京 210044

资助项目:

“十一五”国家科技支撑计划重点项目“人工影响天气关键技术及装备研发” 2006BAC12B00

国家自然科学基金项目 40205001

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出版历程
- 收稿日期: 2006-03-03
- 修回日期: 2007-01-11
- 刊出日期: 2007-08-31

Observation and Analysis of the Aggregation Growth Among Ice-snow Crystals

1.
Key Laboratory for Cloud Physics and Weather Modification, Chinese Academy of Meteorological Sciences, CMA, Beijing 100081
2.
Nanjing University of Information Sciense & Technology, Nanjing 210044

摘要

摘要: 冰雪晶碰并勾连成雪花或雪团的过程是降水的重要机制之一。冰雪晶形态不同导致各类晶动力特性的差异, 因此, 无论从理论、数值试验还是室内模拟研究这一过程都有很大困难。该文就室内、外场试验和自然云的观测, 讨论分析其发生机理和条件。结果表明:冰晶的增长过程有一个与云滴碰并增长相似的加速过程, 冰晶碰并过冷滴形成霰 (雹胚), 凇附长成冰雹; 冰雪晶相互碰并勾连、攀附增长为雪花或雪团, 都是降水质点加速增长的重要过程。此过程仅在水面饱和、过饱和条件下发生, 而水面欠饱和、无液滴 (无云) 时, 冰晶很薄、晶型简单, 无碰并勾连、攀附现象。冰晶在液滴存在的云雾中伴随气流对流、乱流运动中接触碰并勾连成雪花或雪团, 其碰并勾连效率既受晶体形状影响, 亦受晶体表面附着力的影响, 其机制有勾连亦有粘连, 晶型多样, 以相同晶型为主, 温度范围广 (-3~-17 ℃); 其中-13~-17 ℃碰并勾连效率最高, 该层的枝、星状晶是勾连、攀附的主要区域, 亦为冰晶繁生的主要区域、生长率最快, 是人工增雨播撒人工冰核催化效率较高的温度段。
- 冰雪晶碰并勾连;
- 加速降水形成;
- 室内、外试验
Abstract: The process of the ice-snow crystal running together plays an important part in origination of precipitation. It is a focus in cloud physics research. It discusses the cloud and fog that happens in lab and field observations. Result shows that as the droplets coalesce and grow, there is a speed up process also in ice crystals growth, such as snowflake, snow-circular, graupel and hail that coalesce super-cooled droplets and aggregate among ice-snow crystals. Experiments show, in the lab the shapes are fixed basically in temperature of -3.5- -20 ℃. The aggregate among ice-snow crystals only happens in saturated or super-saturated water level vapor pressure in the lab. While in insaturation (no liquid droplets) it does not happen. In 1 m³ chamber their shapes are dendritic and stellar, and their aggregated mechanism is caught by branches appearing in -13- -17.℃ While in 96 m³ chamber the shapes are needle, columnar, dendritic and stellar, the mechanism is adhesion and adhering appearing in -5- -18 ℃. In field observations of natural cloud and fog, the mechanism of the ice-snow crystal running together is adhesion and adhering appearing in -3- -17 ℃, and their shapes are dendritic, stellar, sector, plate, tabular, needle, columnar and columnar bean.The 1 m³ chamber is 1.76 m high and 0.88 m wide, the experiment is made in-3.5- -20 17. The 96 m³ chamber is 14.8 m high, 3.0 m wide, the experiment is made in-5- -18 ℃. The temperature is measure by three Pt resistance thermometers with the difference of 0.1 ℃ to compare with standards one. The sample that burnt for Silver Iodide pyrotechnic is made by deposit method. A great deal ice crystal aggregates into each other appearing in -13- -17 ℃ in 1 m³ chamber when the sample is exposured for 1 minute. But for other temperatures of -3.5- -20 ℃ it does not. While in 96 m³ chamber the aggregation process happens among ice crystals. Their sizes are lager than 1 m³, because the ice crystals could be maintained for a few hours, and there exists torrent and the ice crystal could move with air in 96 m³ chamber. In field observation, the measurement is made by PMS, 2D-C, 2D-P on aircraft in cloud, and by electronic microscope and the samples making for deposit on ground. The shapes of snowflake aggregation vary in cloud in nature because they could exist long in cloud and exhibit convective and torrent features. The ice crystal could interact with them. Another field observation is made by artificial dispersing fog by liquid nitrogen, and samples are measured by electronic microscope for deposit on ground. The ice-snow crystals running into snowflakes by the mechanism of adhering in -3— -8 ℃, and their shapes are hollow columnar, columnar and needle.
- aggregate among ice-snow crystals;
- speed up process;
- experiment in lab and field

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图 1 室内试验的冰晶 (a, b为碰并勾连的枝、星状晶, c, d为其他形状极少粘连)

Fig. 1 Ice cry stals in lab (a, b: aggregated with dendritic and stellar ones; c, d: seldomagg regated)

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图 2 催化后出现冰雪晶 (a, b为显微观测冰晶; c, d为目测雪花)

Fig. 2 Ice and snow crystals after seeding (a, b: observed with the microscope; c, d: observed with eyes)

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图 3 自然降雪的冰雪晶

(a, b为显微观测; c, d为宏观观测)

Fig. 3 Snow crystals in natural snowfall

(a, b: observed with the microscope, c, d: observed with camera)

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表 1 冰晶形状、碰并状况与环境条件的关系

Table 1 Shapes of ice crystal and aggregation varied with air conditions in the cloud chamber

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