Under what circumstances will a tornado happen? Why is its center empty?

When the weather is bad and there is strong wind accompanied by thunderstorm, it is easy to produce tornadoes. Tornadoes are the product of thunderstorm weather in the clouds of the earth's atmosphere. Simply put, it is a form in which a small part of the huge energy of thunderstorms is released in a small range. Tornadoes are very powerful and small in scope. Except in thunderstorm weather and under extremely unstable weather conditions, tornadoes may also be caused by strong convective movement of the air. The wind force of funnel-shaped tornado extending from the bottom of thunderstorm cloud to the ground can reach more than12m, and the maximum wind force can reach more than100m per second. At the same time, it is accompanied by thunderstorms and sometimes hail.

Around the tornado, the air will be attracted by the rapid reduction of the air pressure in the center of the tornado and rotate around the axis of the tornado, and a thin layer of air with a thickness of tens of meters will be formed on the ground. In this range, the airflow will be sucked into the bottom of the tornado vortex and then transformed into a vortex around the axis. Tornado vortex is always cyclonic, and the air pressure at its center is lower than that around it 10%. ?

The probability of a tornado occurring on a water surface with abundant water resources is relatively high, because when the water surface with abundant water resources is not exposed to sunlight, the cooling speed of the water surface is much faster than that of the land, so when the high-altitude sun shines on the water surface, it will form a high-temperature expansion, evaporate the low-altitude water into the sky, resulting in a low-altitude water vapor density reduction. Therefore, no matter where on the ground, as long as the temperature drops rapidly in a large area, and then the water rises to the high altitude, it will cause the airflow to leak downward, and the leaked water vapor will meet the cooled water surface at the same time. When the water surface is almost in a semi-vacuum state, the airflow in the upper air may accelerate from bottom to top, forming a rotating cyclone, and the acceleration at the bottom of the cyclone will aggravate the formation of vacuum, thus making the tornado bigger and bigger.

But tornadoes usually occur in thunderstorm weather in summer, especially from afternoon to night. The attack range is relatively small, generally more than ten meters to several hundred meters in diameter. At the same time, tornadoes exist for only a few minutes, and the longest one will not exceed a few hours.