Destructive power of strong tornadoes can "rig", can you believe it? -Tornado-IT information
The afternoon of June 23, Funing County, Yancheng, Jiangsu, was suddenly heavy hail, Tornado double disasters, casualties is huge, heavy losses. 23rd, at 22 o'clock, the Ministry of Civil Affairs announced, according to preliminary statistics, deaths due to disasters caused by strong convective weather 78 people, injured nearly 500 people for disaster, which injured nearly 200 people and larger number of houses damaged in the affected areas, electric power communication facilities were destroyed, power outages in some areas, communication base station signal.
The disaster we are most afraid of is probably the "tornado" this term.
This disaster movie in Europe and America to see how images are formed? How much power? In fact, every day we can see at home "tornado" similar principles, but we did not know it.
What tornado?
Physics essence, tornadoes are vortices.
The so-called "Vortex", English translation as the Vortex was the rotary motion of the fluid, in general we can generally read as "Vortex".
Image of aerodynamicists describes it as "fluid motion of tendons" Aeronautics and Astronautics Professor Lu Shijia more concise explanation: "fluid nature of vortex, because fluids can't rub rub rub out of the vortex. ”
Here the "rub", refers to the role of shear stress in the fluid. Such as aircraft, ships, automobiles, trains, such as objects moving in air, close to the air at the surface due to the adhesion on the surface will be together with movement of objects, and fluid is still in the distance, which creates a fluid "rubbing" force.
? Rear "roll" out air Vortex
Is the nature of many of the tornado vortex, common Vortex include:
Spiral galaxy: space spiral galaxy, is a largest scale vortex in nature which is "light years".
?2013 United States NASA (NASA) spiral galaxies from the Hubble telescope NGC6984
Typhoons, hurricanes, tropical storms, tropical cyclones
In weather forecasting, satellite images, we can often see that the rotation of the cloud shows a large-scale fluid Vortex, its radius of hundreds of kilometers.
Tornado
In 2003, the United States Terra satellite captures images of the hurricane Kate. Filming Kate when the hurricane sustained winds of 115 miles per hour, moving westwards at a speed of 12 miles per hour
In accordance with the definition of Meteorology: Tornado is an intense, small scale air Vortex , were strongly unstable weather conditions, produced by strong convective air movement is usually the funnel cloud extending from the thunderstorm cloud to the ground the strong cyclone. Tornado low central pressure, the Centre up to 100-200 meters per second wind, with devastating force.
2008 United States over Kansas Prairie tornado
2009 United States appeared on the Saint Johns River waterspout
Other similar to dust storms, tsunamis are also common forms of vortex in nature.
2001 United States NASA satellite photograph sandstorms in Asia Vortex
2011 Japan after the earthquake and tsunami sea formed giant whirlpool
In daily life, we often see this phenomenon: in a sink or tub filled with water, plug, forming a whirlpool that science called "bathtub Vortex", this is a typical phenomenon of vortex.
Sinks in the bathtub Vortex
? United States Science and Technology Museum in the simulated tornado "bathtub Vortex"
So I can say, at home in the kitchen or bathroom, we can easily simulate the physical mechanism of tornadoes.
The formation mechanism of tornadoes
Now that you know a tornado is a kind of vortex, what about how tornadoes form?
In April this year, Guazhou County, Jiuquan city, Gansu province, Yuan Quan elementary school spring sports, weather conditions are very good, but suddenly there was a cyclone, a 9 year old boy instant was rolled a few meters high, which is "tornado"?
?? picture
In fact, this is just a small scale flow instabilities caused by us "dust devil", similar to the early April, Beijing Beihai Park there have been dust devil, then flipped a couple of boats.
Must be a tornado caused by Mesoscale flow instability, with an average diameter of 200-300 metres, minimum dozens of meters in diameter, and up to 1000 meters, time usually lasts for a few minutes until more than 10 minutes, up to a few hours, moving at 15 mph to 70 mph.
The formation of tornadoes associated with thunderstorm clouds, thunderstorms are a fraction of the enormous amounts of energy in a very small area free, brought energy to the tornado. And because part of the pillar of cloud stretching down the clouds and turn down level convergence, similar to the skater rotates in the clamping arm, spinning faster and faster, this stretch of the Vortex tube, rotate very fast, forming a funnel-shaped cloud, form the shape of a tornado.
▲ Skaters arm clamping will improve their rotation speed
Particular tornado formation is divided into 4 stages:
1. the instability of the atmosphere have a strong updraft, the largest rapids in transit the influence it is further strengthened.
2. on the vertical speed and direction of wind shear interaction updrafts in the middle of the troposphere begins to rotate to form a mesocyclone.
3. as the mesocyclone to the developments on the ground and reaching up, thinner and increase of its own. Meanwhile, a small area of enhanced convergence, born formed inside the tornado cyclone, form the core of a tornado.
4. the tornado core rotation and cyclones are different, it's strong enough to make tornado stretched all the way to the ground, when the scroll when it reaches the ground level, sharp decline in surface pressure, sharp increase in wind speed on the ground, forming a tornado.
? Tornado formation (source of the mechanics and practice)
Tornado air
In simple terms, the appearance and disappearance of the tornado, are the processes of flow instability.
Encounter a tornado how to save ourselves?
Leave hazardous places for housing, or other simple temporary accommodations to more robust housing from nearby.
In the car, left in time, reach the low-lying land to escape, because the car does not have the defense capability of the tornado, once the cars and people at the same time by a tornado rolled up, more dangerous.
Rapidly in the direction perpendicular to the direction of movement of the tornado run, fell on low-lying ground, trenches, away from trees, billboards, telephone poles, fences, so as to avoid being hit, or electric shock.
Escape the tornado safe place is located in an underground space or place on the ground, all buildings at this time is not the most secure place to avoid.
破坏力超强的龙卷风在家里就能“造”，你信吗？ - 龙卷风 - IT资讯
6月23日下午，江苏盐城阜宁县突遭强冰雹、龙卷风双重灾害袭击，伤亡巨大，损失惨重。23日22时，国家民政部发布消息，据初步统计，强对流天气造成因灾死亡78人，因灾受伤近500人，其中重伤近200人，受灾地区房屋倒损数量较多，电力通信设施被破坏，部分地区电力中断，通信基站无信号。
此次灾害中最令大家畏惧的恐怕就是“龙卷风”这个名词。
这个在欧美灾难大片中才能见到的景象到底是怎样形成的？有多大威力？其实，我们每天在家里都能见到“龙卷风”相似的原理，只不过我们并不认识它而已。
龙卷风是什么？
从物理学本质上讲，龙卷风其实是涡旋的一种。
所谓“涡旋”，英文翻译为vortex，是流体团的旋转运动，一般我们可以通俗的理解为“涡”。
空气动力学家形象的将其描述为“流体运动的肌腱”，北京航空航天大学陆士嘉教授更简明地解释为：“流体的本质就是涡，因为流体经不住搓，一搓就搓出了涡。”
这里的“搓”，是指作用在流体上的剪切力。比如飞机、船舰、汽车、火车等物体在空气中运动，紧贴在物面上的空气由于黏附在物面上，会被物体带着一起运动，而远处的流体却在静止中，这就产生了对流体发生“搓”的剪切力。
▲飞机尾部“搓”出的气流涡旋
龙卷风就是大自然中众多涡旋的一种，常见的涡旋包括：
涡旋星系：宇宙空间的涡旋星系，是大自然中尺度最大的涡旋，其尺度是“光年”。
▲2013年美国宇航局(NASA)利用哈勃望远镜拍摄的旋涡星系NGC6984
台风、飓风、热带风暴、热带气旋
在气象预报的卫星云图上，我们经常可以看到由大团白云显示的旋转大尺度流体涡旋，其半径可达数百公里。
龙卷风
2003年，美国Terra卫星捕获到的Kate飓风照片。拍摄时Kate飓风持续风速为115英里/小时，以12英里/小时的速度向西移动
按照气象学的定义：龙卷风是一种强烈的、小范围的空气涡旋，是在强烈不稳定天气条件下，由空气强烈对流运动产生的，通常是由雷暴云伸展至地面的漏斗云产生的强烈旋风。龙卷中心气压很低，中心风力可达每秒100—200米以上，具有极大的破坏力。
2008年美国堪萨斯州大草原上空的陆龙卷
2009年美国圣约翰河上出现的水龙卷
其他类似于沙尘暴、海啸等也都是自然界常见涡旋的表现形式。
2001年美国宇航局卫星在亚洲上拍摄到的沙尘暴涡旋
2011年日本海啸和地震过后海上形成巨大的漩涡
在日常生活中，我们经常看到的这种现象：在盛满水的洗手池或者澡盆中，将塞子拔掉，会形成一个漩涡，科学上叫做“澡盆涡”，这就是典型的涡旋现象。
洗手池中的澡盆涡
▲美国科技馆中模拟龙卷风的“澡盆涡”
所以可以说，在家里的厨房或者浴室里，我们就可以轻松地模拟出龙卷风的物理机理。
龙卷风的形成机理
既然知道了龙卷风属于涡旋的一种，那么龙卷风是如何形成的呢？
今年4月份，甘肃省酒泉市瓜州县渊泉小学举行春季运动会，天气状况非常好，但是突然就刮起了旋风，一名9岁男孩瞬间被卷起几米高，这就是“龙卷风”吗？
▲现场画面
其实，这只是很小尺度的气流不稳定性造成的，一般我们成为“尘卷风”，类似的还有4月初，北京北海公园也出现过尘卷风，当时还掀翻了几艘小船。
而龙卷风必须是由中尺度的气流不稳定性造成的，其平均直径为200-300米，最小直径几十米，最大1000米左右，持续时间一般几分钟至十几分钟，最多不超过几小时，移动速度在15米/秒至70米/秒。
龙卷风的形成与强雷暴云有关，雷暴巨大的能量中的一小部分在很小的区域集中释放，给龙卷风带来了能量。同时由于云层的一部分云柱向下伸展，并旋转向下水平辐合，类似于滑冰运动员在旋转时夹紧手臂，使得旋转速度越来越快，这种伸展的涡管旋转速度非常快，形成了漏斗状的云，构成了龙卷风的形状。
▲滑冰运动员手臂夹紧会提高旋转速度
具体来说龙卷风形成分为4个阶段：
1.大气的不稳定性产生强烈的上升气流，由于急流中的最大过境气流影响，它被进一步加强。
2.由于与在垂直方向上速度和方向均有切变的风相互作用，上升气流在对流层的中部开始旋转，形成中尺度气旋。
3.随着中尺度气旋向地面发展和向上伸展，它本身变细并增强。同时，一个小面积的增强辐合，即初生的龙卷在气旋内部形成，形成龙卷核心。
4.龙卷核心中的旋转与气旋中的不同，它的强度足以使龙卷一直伸展到地面，当发展的涡旋到达地面高度时，地面气压急剧下降，地面风速急剧上升，形成龙卷风。
▲龙卷风形成机理(图片来源自《力学与实践》)
龙卷风中的气流方向
简单来说，龙卷风的形成和消失，都是气流运动不稳定的过程。
遇到龙卷风如何自救？
立刻离开危险房屋、活动场所或其他简易临时住处，到附近比较坚固的房屋内躲避。
如在汽车中，应及时离开，到达低洼地躲避，因为汽车本身没有防御龙卷风的能力，一旦汽车和人同时被龙卷风卷起，危害更大。
迅速朝龙卷风移动方向的垂直方向跑动，伏于低洼地面、沟渠等，远离大树、电线杆、广告牌、围墙等，以免被砸、被压或发生触电事故。
躲避龙卷风最为安全的地方是位于地下的空间或场所，地面上所有建筑物此时都不是最安全的躲避场所。