How is a whirlwind formed?

A cyclone is a swirling air vortex, which flies into the air with dust carried by the ground. This vortex is a natural phenomenon caused by air flow.

When the air flows around the uneven places such as trees, hills and buildings on the ground, or when the air rubs against the ground, the direction should be changed quickly, and then a vortex moving with the airflow will be generated, thus blowing a whirlwind. However, this kind of cyclone is rare and very small.

The main reason for the formation of cyclones is that when a place is very hot by the sun, the air here will expand and some air will be squeezed up. After reaching high altitude, the temperature will gradually decrease, start to flow around and finally sink to the ground. At this time, the air in the heated area will decrease, and the air pressure will also decrease, while the surrounding temperature is low and the air density is high. In addition, the heated air will fall from the air, so the air will increase. The air pressure has increased significantly. In this way, air will flow from the places with high air pressure around to the places with low air pressure in the center, just like water flows to lower places. However, because the air flows on the earth, and the earth is constantly rotating from west to east, the air will be affected by the rotation of the earth in the process of flowing, and gradually shift to the right (the original north wind is deflected into northeast wind, the south wind is deflected into southwest wind, the west wind is deflected into northwest wind, and the east wind is deflected into southeast wind). So the cold air blowing from all directions rotates around the heated low-pressure area, turning into an air vortex opposite to the clockwise rotation direction of the clock, forming a whirlwind.

In the center of this cyclone, due to the rising warm air and the continuous rotation of the surrounding air, it is easy to roll up dust, leaves, paper scraps and so on. It becomes air on the ground and flies with the flow of air. If the cyclone is strong, sometimes some small animals on the ground, such as small snakes and bugs, are swept into the air and gone with the wind in the dust.

Generally, the height of small cyclones is not too high. When it is rubbed by the ground or blocked by houses and trees, it gradually dissipates and becomes an ordinary wind.

Some people may ask: because the ground is easy to produce cyclones when heated, it is hotter in summer than in spring. Why are there fewer cyclones in summer and more cyclones in spring? This is because although the weather is very hot in summer, the ground vegetation is green, the land is wet, and the temperature difference is not big, so there are few cyclones in summer. However, in spring, when the leaves have not all grown out, the grass has just sprouted, the farmland is bare, there is no shelter everywhere, and it is easy to get hot, which makes the air temperature on the ground change greatly and it is easy to blow cyclones.

Cyclones can fly into the air with dust and messy papers, and of course they can also bring heat and water vapor from the ground into the air. Therefore, heat and water vapor are vertically mixed in the air, and the vertical distribution of heat and water vapor in the air is uniform. The cyclone is very small near the ground, and the vertical exchange effect is not great, so a special microclimate is formed in the air layer near the ground.

In addition, strong tropical cyclones occurring in the southern hemisphere and the northern Indian Ocean are also called cyclones.