Why is there wind?
Unlike some other natural phenomenon, wind is not caused by one single event. Wind is caused by a combination of a few simultaneous happenings:
+ temperature and dilatation
+ the rotation of the planet
+ humidity and landscapes
The basic cause is temperature. During the day, although the sun’s rays heat the land and the ocean at the same time, they do not heat evenly. Land warms up faster than the ocean; therefore any air over it dilates and expands faster than it does over water. This dilatation causes hot air to go up, leaving an empty space on the surface. The empty space cannot remain empty for long, so it is filled with cooler air from the surrounding areas. This motion causes wind and it can usually be felt coming from the ocean to the land during the day.
During the night, we experience the same phenomenon but backwards. As there are no sun rays, both the ocean and land cool off, but not evenly. As land cools faster than the ocean, the air above it cools down faster, causing it to come down near the surface. This motion causes an empty space higher in the atmosphere, forcing hotter air from the oceans to move and fill it up. This causes another wind during the night and can usually be felt as coming from land to ocean during the night.
In addition, we need to add that the Earth rotates fast. We are talking about a speed of around 465 m/s (and I say "around" because the speed changes now and then) at the equatorial 0º latitude. Winds do not move as fast, so this causes an inertia phenomenon on land around the equator; just in the area where sun rays fall the most. The combination of the inertia caused by rotation and the temperature change caused by the constant sun light in the equatorial area causes a permanent cycle of winds all over the planet. Hot air near the equatorial area will rise leaving an empty space below for the same reason. The empty space is filled up with cooler air coming from the poles. Hot air then moves towards the poles, cooling down and coming down again. The winds in the equatorial area are called trade winds, causing air to constantly flow from the equatorial area to both poles and vice versa all the time.
Yet there is a third phenomenon involved in winds, and it is caused by humidity and landscapes. Winds move soil, scatter seeds, move clouds from one place to the other. Winds collide with mountains and change direction too. When there is humidity in the area, winds move slower as if they were slowed down by particles of water. Where there is low humidity, winds move fast, causing air erosion and creating deserts. Where there is high humidity, winds slow down, preventing humidity from scattering to other areas. This creates jungles and rainforests.
Winds are more important than they appear!
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