天空为什么会下雨

下雨是一种自然现象。天上的雨是从哪里来的呢？做了下面的实验，你就明白了。[编者按]     

能预报天气的动物

如果猪在上午叼草,预示36 h后有雨,过午叼草,预示20 h后有雨;夜幕渐落,羊却不想回家,只顾低头吃革,不但吃得时间很长,也不爱走动,这预示明天将要下雨;天近薄暮,鸡却迟迟不肯上架,在地面上来回走动、觅食,还不时地抖动羽毛,这预示很快就要下雨了.     

漏网之鱼

一个下雨的周日晚上，TOM先生正在看书。突然，门铃响了，他把门打开。就叹了口气，站在外面的，不是别人，正是TOM的债主：SEVER。     

为什么只有乌云下雨，白云再多也不会变成雨降下来？

云彩看起来是白亮还是乌黑，主要由云的厚度和云中粒子数量、大小，以及太阳所处位置所决定。阳光从云顶照射下来时，被云中大大小小的小水滴或者小冰晶散射和折射掉。     

古墓大树一出太阳就下雨

四川省眉山市仁寿县虞丞乡丞相村,因南宋抗金名将虞允文安葬在此而得名。2009年2月13日,有一行人来古墓前祭拜,古墓看护人带领来者围着古墓转了一圈,当他们有说有笑地从古墓右侧经过时,突然,一阵如黄豆般大小的雨点从天而降,其中一人的衣袖还被突如其来的“大雨”淋透了。“当时是中午12点左右,正是艳阳高照,哪来的雨？”众人赶紧仰头观察,这才发现“大雨”并非从天而降,而是从古墓上一棵棉纱树上落下来的。之后,只要出太阳,这颗棉丝树就会出现下雨情况。     

头大=聪明？玉米博士请回答

如果你哪天走在路上自自语：“今天会不会下雨啊？”从你身旁经过的老爷爷突然停下：“我认为不会！你看那些云……从气象学来看……根据科学常识来讲……所以下雨的几率很小。”咳咳,恭喜你!你见到了传说中的玉米博士！     

千年古墓上的怪树会下雨

2009年2月份，四川省仁寿县虞城乡出现了一件怪事：几个村民在一个小路上走着，突然飘起了雨点，并且其中一个人的衣袖竟然被突如其来的大雨打湿了，正当他们想往家赶时却发现艳阳高照，没一丝云彩。他们抬头仔细观察，确实在下雨，毛毛细雨夹杂着大雨点，而雨竟然是从树上落下的，于是，大树会下雨的消息不胫而走。     

Response of tree-ring width to rainfall gradient along the Tianshan Mountains of northwestern China

By comparing the long-term tree-ring growths at various geographic scales, we can make clear the effects of environmental variations on tree growth, and get an understanding of the responses of forest ecosystems to the possible changes in global and regional climate. Radial tree-ring growth of Picea schrenkiana and its relationship to air temperature and precipitation were investigated across longi- tude transects on the north slopes of the Tianshan Mountains in northwestern China. Tree-ring samples were collected and residual chronologies were developed for three different regions along a gradient of decreasing precipitation from west to east. Response-function analysis was conducted to quantify the relationships between tree-ring chronologies and climate variables, such as monthly mean temperature and monthly precipitation from 1961 to 1998, using the PRECON software program. The statistical characteristics of the chronologies showed that the three chronologies constructed in this study con- tained significant environmental signals and were well suitable to reveal the impacts of climatic change on tree growth and forest productivity. Annual ring-width variations were similar among the three sites, but the variability was greatest in the east. This research showed that the growth trends of Picea schrenkiana in the Tianshan Mountains have not followed a uniform pattern. Response-function analy- sis indicated that there were significant correlations between tree growth and climatic factors in all the three regions, among which precipitation was the principal. With decreasing precipitation, the response of tree-ring widths to increasing temperature changed from a positive to a negative correlation. As for precipitation, the positive relationship to tree-ring width always dominates. It could be expected that with increased temperature and decreased precipitation, the importance of precipitation to tree growth would increase, and the response of tree growth to environmental changes would also increase. This study emphasizes the importance of regional-scale investigations into the biosphere-climate interac- tions. The results of this research indicated a substantial increment of tree-ring radial growth as a re- sult of warmer and wetter climate in the eastern regions. However, climate change will have less effect on forest growth and primary production in the western regions.     

下雨时，也要关注健康

提起下雨与健康的关系．人们自然会联想被雨水清洗后洁净、清新的空气以及空气中大量的负离子。似乎下雨肯定有益于健康，事实上，很多雨对人体健康是不利的。