What is a tornado?
(1) The instability of the atmosphere produces a strong updraft, which is further strengthened due to the influence of the maximum transit airflow in the rapids.
(2) Due to the interaction with the wind with shear speed and direction in the vertical direction, the updraft starts to rotate in the middle of the troposphere, forming a mesoscale cyclone.
(3) With the development and upward extension of mesoscale cyclone to the ground, it becomes thinner and stronger. At the same time, a small area to strengthen cooperation, that is, the primary tornado is formed inside the cyclone, and the same process of producing the cyclone forms the tornado core.
(4) The rotation in the tornado core is different from that in the cyclone, and its intensity is enough to make the tornado extend to the ground. When the developing vortex reaches the ground, the ground air pressure drops sharply and the ground wind speed rises sharply, forming a tornado.
Extended data:
First, the basic characteristics:
Tornado is a natural phenomenon with certain destructive power. Generally speaking, a tornado is a whirlwind. When it touches the ground, its diameter varies from several meters to several hundred meters, with an average of about 250 meters and a maximum of about 1000 meters.
The diameter can reach several kilometers in the air, and the maximum is 10 km. The maximum wind speed can reach 150 km to 450 km per hour, and the tornado usually lasts only a few minutes, but the longest is only a few hours.
Everywhere I went, I was robbed. The funnel-shaped center of tornado is composed of inhaled dust and condensed water vapor, which is a visible "dragon mouth". On the ocean, especially in the tropics, similar scenes are called sea tornadoes.
Tornadoes are usually extremely fast. It is not surprising that the wind speed is 100 m per second, even reaching more than 175 m per second, which is five or six times larger than the typhoon 12. The range of wind is very small, generally the diameter is only 25~ 100 meters, and only in rare cases can the diameter reach more than one kilometer; It takes only a few minutes from occurrence to disappearance, at most a few hours.
Most tornadoes rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere, with some exceptions. The exact mechanism of tornado formation is still under study, and it is generally believed to be related to the violent activities of the atmosphere.
Second, EF classification.
EF0: The wind speed is 65-85 miles per hour, which is about 105- 137 kilometers per hour. Although weak, it is still enough to blow off branches, roll up lighter fragments, break glass, and some chimneys will be blown off. (The probability of occurrence is extremely high, 53.5%)
EF 1: the wind speed is 86- 1 10 miles per hour, which is about 138- 177 kilometers per hour. They can blow away roofs and overturn prefabricated houses, and some lighter cars will be blown over or scraped off the road. (High probability of occurrence, 3 1.6%)
EF2: Wind speed per hour11-135 miles, which is about 178-2 17 kilometers per hour. They can blow heavy licorice bags hundreds of meters away, uproot a big tree and blow trucks off the road. (The probability of occurrence is moderately low, 10.7%)
EF3: Wind speed per hour 136- 165 miles, which is about 2 18-266 kilometers per hour. They can blow down a heavy car, blow trees off the ground, destroy more than half of the houses and derail the train. (Low probability of occurrence, 3.4%)
EF4: The wind speed is 166-200 miles per hour, which is about 267-322 kilometers per hour. They can blow a car away, raze a solid house to the ground and blow trees hundreds of meters high. (The probability of occurrence is very low, 0.7%)
EF5: The wind speed EF5:EF5 exceeds 200 miles per hour, that is, it exceeds 322 kilometers per hour. Houses were completely destroyed, cars were completely blown off, asphalt on the road was scraped off, and trucks, trains and trains all left the ground. (The probability of occurrence is low or high, 20%-45%)
Baidu encyclopedia-tornado