Many people know that a large amount of precipitation falls in low (equatorial) latitudes. Also, this zone of our planet is the source of many hurricanes and tropical typhoons. The fault of all these processes is the so-called trade winds. The question of what the trade winds is discussed in detail in the article.
Solar radiation and the origin of winds
Before turning to the answer to the question of what the trade winds are, one should consider the very concept of "wind" and for what reasons it arises. This word means translational horizontal movement of air masses. This occurs due to the pressure difference in different zones of the earth's atmosphere. In turn, this pressure difference is due to the uneven heating of the earth's surface and oceans located at different latitudes.
It is known that the sun's rays hit the Earth almost at an angle of 90 o in the equator. Further, with increasing latitude, this angle decreases, respectively, and the amount of heat that the earth's surface receives from the Sun decreases. The weaker the soil and water surface, the lower will be the temperature of the air in contact with them. Air pressure depends on its temperature: the higher it is, the lower the density of the gas substance is, which means its pressure also drops. Thus, strong heating of the equatorial zone of the planet leads to a decrease in air pressure at low latitudes.
Sustainable tropical climate winds
Now we can proceed to answer the question of what the trade winds are. This word means stable constant and moderate wind forces that blow from the tropical zones of the Northern and Southern Hemispheres to the equatorial region.
The mechanism of the occurrence of the trade winds is as follows: the air at the equator is very hot, as a result, its density decreases, and it rises up due to the physical process of convection. As a result, a zone of reduced pressure is created, which is filled with air masses that came from the tropics.
The described mechanism assumes that the trade wind should blow from north to south in the Northern Hemisphere and from south to north in the South. In reality, its direction has a western character. In particular, in the Northern Hemisphere it blows from the north-east to the south-west, in the Southern - from the south-east to the north-west. The reason for this nature of the movement of air masses is the action of the Coriolis force associated with the rotation of the Earth around its axis. It is this force that leads to the displacement of the trade winds in a westerly direction.
Hadley Cell
The trade winds are constant winds, the range of which extends up to 30 o latitude in both hemispheres. The indicated region is applicable to the issue of atmospheric circulation; it is customary to call the Hadley cell. John Gadley - an English lawyer who lived in the XVIII century, who was interested in the question of what the trade winds are and why they are blowing in a constant direction. The Hadley cell explains heat transfer from the equator to the tropical regions of the Earth. So, the heated equatorial air rises to a height of about 1-1.5 km and begins to move in the direction opposite to the trade winds. Reaching latitude 30 o , the air masses descend.
The intra-tropical zone of the convergence of the trade winds (WCC)
Knowing what the trade winds are and in what direction they are blowing, it can be assumed that these winds should meet at the equator. Indeed, this is what is happening, and their meeting place is called the All-Russian Exhibition Complex (transcript in the name of the item). VZKP is a zone of silence, which is a belt around the equator 200-300 km wide. VZKP is a dynamic formation, that is, its coordinates can vary during the year by several degrees of latitude. So, in the summer for the Northern Hemisphere, it shifts to the north, in winter, on the contrary, the SCW is located in the Southern Hemisphere.
As already mentioned, the WZKP is a zone of silence, or calm. There is practically no wind. However, it is characterized by constant ascending flows of hot air, which condenses and forms cumulus clouds and clouds of great thickness (2-18 km from the land surface). That is why the WZKP is an area of โโtropical showers.
At the borders of the Hadley cell, that is, near 30 o latitude in both hemispheres of the planet, there are two more zones of convergence of the trade winds. They are formed due to the downward flow of air from equatorial latitudes. In these zones there is practically no precipitation, which led to the formation of deserts (Sahara, Kalahari).
How did people use trade winds in past centuries?
Since the trade winds are stable moderate winds (3-4 points on the Beaufort scale) that blow westward, they were used by sailors when traveling to the American continents. At the same time, ships often fell into the zone of the air defense zone (full calm area), where a whole crew often died, because the ship stood still.
It is curious to note that in Russian the word "trade wind" comes from the Spanish expression viento de pasada, which literally means "constant wind that is used to move." In Spanish itself and in many European languages, another name is used to designate the trade winds, based on the Latin word alis, which means "smooth, gracious, delicate, without impetuosity."