Frivolity in the modern dictionary is synonymous with inconstancy, changeability. But the trade winds completely break this statement. Unlike breezes, seasonal monsoons, and especially winds caused by weather cyclones, they are constant. How are the trade winds formed and why are they blowing in a strictly defined direction? Where did the word “trade wind” come from in our language? Are these winds really so constant and where are they localized? You will learn about this and much more from this article.
The meaning of the word "trade winds"
During the sailing fleet, the wind was of paramount importance for navigation. When he always blew exactly in the same direction, one could hope for a successful outcome of a dangerous trip. And such a wind the Spanish sailors dubbed "viento de pasade" - conducive to movement. The Germans and Dutch included the word “Pasade” in their nautical dictionary of navigation terms (Passat and passaat). And in the era of Peter the Great, this name also penetrated the Russian language. Although in our high latitudes the trade winds are a rarity. The main place of their "habitat" is between the two tropics (Cancer and Capricorn). The trade winds are observed and further from them - up to the thirtieth degree. At a considerable distance from the equator, these winds lose their strength and are observed only in large open spaces, above the oceans. There they blow with a force of 3-4 points. Off the coast, trade winds are transformed into monsoons. And even further from the equator give way to the winds generated by cyclonic activity.
How the trade winds are formed
Let's do a little experiment. Put a few drops on the ball. Now spin it like a yule. Take a look at the drops. Those that are closer to the axis of rotation remained immovable, and those 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. Opposite winds form from this movement. When the point is close to the poles, it makes a smaller circle per day than the one at the equator. Therefore, the speed of its movement around the axis is slower. Due to friction with the atmosphere, air currents do not arise in such subpolar latitudes. Now it’s clear that the trade winds are the steady winds of the tropics. At the same equator, the so-called calm strip is observed.
Trade winds
It is not difficult to trace dropwise on the ball that they spread in the direction opposite to rotation. This is called the Coriolis force. But to say that the trade winds are winds blowing from east to west 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 specular reflection, on the other hand from the equator. That is, in the southern hemisphere trade winds blow from the southeast to northwest.
Why is the equator so attractive to air masses? In the tropics, as you know, a constant area of high pressure is established. And the equator, on the contrary, is low. If we answer the children's question, where does the wind come from, we will state the natural history truth. Wind is the movement of air masses from layers with a high pressure to an area with a lower pressure. The periphery of the tropics in science is called “Horse Latitudes”. From there, the trade winds are galloping into the "Calm Strip" above the equator.
Constant wind speed
So, we understand the area of distribution of the trade winds. They form in both hemispheres of the Earth at a latitude of 25-30 ° and decay near the calm zone somewhere around 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 trade winds. Born in regions with a hot and arid climate, these winds contribute to the development of deserts such as Kalahari, Namib and Atakama.
Are they so constant?
Over the mainland trade winds collide with local winds, sometimes changing their speed and direction. For example, in the Indian Ocean, due to the special configuration of the coast of Southeast Asia and climatic characteristics, trade winds turn into seasonal monsoons. As you know, in summer they blow from the cool sea towards the heated land, and in winter - vice versa. However, the assertion that the trade winds are winds of tropical latitudes is not entirely true. In the Atlantic, for example, in the Northern Hemisphere, they blow in the winter and spring in the range of 5-27 ° N, and in the summer and autumn 10-30 ° N. As early as the eighteenth century, John Gadley, a British astronomer, gave this strange explanation to this strange phenomenon. The band of calm does not stand at the equator, but moves after the Sun. Thus, by the date when our star is at its zenith above the tropic of Cancer, the trade winds are shifting to the north, and in the winter to the south. Constant winds and power are not the same. The trade wind of the southern hemisphere is more powerful. He almost never encounters obstacles in the form of land. There it forms the so-called “roaring” forties.
