Trade winds are steady winds

Windiness in the modern dictionary is synonymous with impermanence, changeability. But the trade winds completely break this statement. Unlike breezes, seasonal monsoons and the more winds caused by weather cyclones, they are constant. How are trade winds formed and why are they blowing in a strictly defined direction? Where did this word come from in our language - the "trade wind"? Are these winds constant and where are they localized? About this and many other things you will learn from this article.

The meaning of the word "trade winds"

At the time of the sailing fleet, the wind was of paramount importance for navigation. When he always blew in the same direction, one could hope for the safe outcome of a dangerous journey. And such a wind Spanish navigators dubbed "viento de pasade" - favoring displacement. The Germans and the Dutch included the word "pasade" in their naval dictionary of navigational terms (Passat and passaat). And in the era of Peter the Great this name penetrated into the Russian language. Although in our high latitudes the trade winds are a rarity. The main place of their "habitat" - between the two tropics (Cancer and Capricorn). Trade winds are observed and further from them - up to the thirtieth degree. At a considerable distance from the equator, these winds lose their power and are observed only in large open spaces, above the oceans. There they blow by force of 3-4 points. At the coast trade winds are transformed into monsoons. And further away from the equator is the place given to the winds generated by the cyclonic activity.

How are the trade winds formed

Let's do a little experiment. We will put a few drops on the ball. And now we'll twirl it like a yule. Look closely at the drops. Those of them that are closer to the axis of rotation, remained immovable, and located on the sides of the "yule" spread out in the opposite direction. Now imagine that the ball is our planet. It spins from west to east. This movement creates opposite winds. When the point is located close to the poles, within a day it makes a smaller circle than the one at the equator. Therefore, the speed of its movement around the axis is slower. From the friction with the atmosphere, no air currents appear in such polar latitudes. Now it is clear that the trade winds are stable winds of the tropics. At the very equator, there is a so-called calm strip.

Direction of trade winds

By drops on the ball, it is easy to see that they are spreading in the direction opposite to the rotation. This is called the Coriolis force. But to say that trade winds are winds blowing from east to west, it would be wrong. In practice, in the Northern Hemisphere, air masses deviate from their main vector to the south. The same thing happens, only in the mirror image, on the other side of the equator. That is, in the Southern Hemisphere the trade winds are blowing from the southeast to the northwest.

Why is the equator so attractive to air masses? In the tropics, as is known, a constant high-pressure region is established. And the equator, on the contrary, is low. If we answer the children's question, where does the wind come from, then we will lay down the natural history of truth. The wind is the movement of air masses from layers with high pressure to a region with a lower one. The periphery of the tropics in science is called "Horse Latitudes". From there the trade winds blow in the "Calm strip" above the equator.

Speed of constant winds

So, we understood the distribution area of the trade winds. They are formed in both hemispheres of the Earth at a latitude of 25-30 ° and are damped near the calm zone somewhere at 6 degrees. The French believe that the trade winds are "right winds" (vents alizes), very convenient for sailing. Their speed is small, but constant (five to six meters per second, sometimes it reaches 15 m / s). However, the power of these air masses is so great that they form the trade winds. Born in regions with a hot and arid climate, these winds contribute to the development of deserts such as Kalahari, Namib and Atacama.

Are they permanent?

Over the continents trade winds collide with local winds, sometimes changing their speed and direction. For example, in the Indian Ocean, because of the particular configuration of the coast of Southeast Asia and climatic characteristics, trade winds are transformed into seasonal monsoons. As you know, they blow from the cool sea in the summer towards the heated land, and in winter - on the contrary. However, the assertion that trade winds are winds of tropical latitudes is not entirely true. In the Atlantic, for example, in the Northern Hemisphere, they blow in winter and spring within 5-27 ° N, and in summer and autumn 10-30 ° N. This strange phenomenon in the XVIII century gave a scientific explanation of John Gadley, a British astronomer. The band of calm does not stand on the equator, but moves after the Sun. Thus, by the date when our luminary stands at the zenith above the tropic of Cancer, the trade winds are shifting towards the north, and in the winter - to the south. Constant winds are also not constant in strength. The trade wind of the Southern Hemisphere is more powerful. He almost does not meet obstacles on his way in the form of land. There it forms the so-called "roaring" forties.

Trade winds and tropical cyclones

To understand the mechanics of typhoon formation, it is necessary to understand that in each hemisphere of the Earth two constant winds are blowing. All that we have described above refers to the so-called lower trade winds. But the air, as is known, is cooled when climbing to the altitude (an average of one degree every hundred meters of the rise). Warm masses are lighter and rush to the sky. Cold air tends to fall down. Thus, opposite trade winds appear in the upper atmosphere. These are winds blowing in the Northern Hemisphere from the south-west, and lower from the equator - from the north-west. The temperature inversion inside the trade winds sometimes changes the stable direction of the two layers. There is a zigzag twisting of warm, saturated with moisture and cold air masses. In some cases, tropical cyclones are gaining strength from a hurricane. The same vector of direction that is characteristic of the trade winds, brings them to the west, where they and bring down their destructive power to coastal areas.