Wind
The wind is the large-scale flow of air in the Earth's atmosphere. In the atmosphere, mass movement of air according to differences in atmospheric pressure. Günter D. Roth defines it as "the compensation of atmospheric pressure differences between two points".
In meteorology, winds are often named according to their strength and the direction from which they blow. Sudden increases in wind speed for a short time are called gusts. Strong winds of intermediate duration (approximately one minute) are called squalls. Long-duration winds have various names depending on their average strength, such as breeze, temporal, storm, hurricane i> or typhoon. Wind can occur on various scales: from stormy flows that last tens of minutes to local breezes generated by the different heating of the earth's surface and lasting several hours, and even global, which are the result of the difference in energy absorption between the different geoastronomical zones of the Earth. The two main causes of large-scale atmospheric circulation are differential heating of the Earth's surface depending on latitude, inertia, and centrifugal force produced by the planet's rotation. In the intertropical zone, the difference in atmospheric pressure between the oceans (warm and humid air mass) and the continents (warm and dry air masses) during the summer in the northern hemisphere, that is, between June and September, gives rise to to the formation of seasonal winds between the Indian Ocean and the Asian continent and thermal depressions in the interior of the continents, especially in Asia and, to a lesser degree, in North America, between the Gulf of Mexico and the interior of the United States States (the Midwest), are the reason for the monsoon circulation of the winds, which during the hottest season move inland and drive the monsoon circulation.
In coastal areas, the sea breeze/land breeze cycle can define local winds, while in areas with varied relief valley and mountain breezes can dominate local winds.
In human civilization, the wind has inspired mythology, affected historical events, extended the reach of transportation and warfare, and provided a source of energy for mechanical work, electricity, and leisure. Wind has powered the voyages of sailing ships across Earth's oceans. Hot air balloons use the wind for short trips, and powered flight uses it to generate lift and reduce fuel consumption. Areas with wind shear caused by various weather phenomena can cause dangerous situations for aircraft. When the winds are strong, trees and human-made structures can be damaged or destroyed.
Winds can shape landforms through a number of aeolian processes, such as the formation of fertile soils (for example, loess) or their destruction through erosion. Dust from large deserts can be moved great distances from its source by prevailing winds, and winds that are accelerated by rugged topography and associated with dust storms have been given regional names in different parts of the world because of its significant effect on these regions. Wind affects the spread of wildfires, as it can stop or speed up the fires. It also disperses the seeds of certain plants, and makes possible the survival and dispersal of these plant species, as well as populations of flying insects. In combination with the cold temperatures, the wind has a negative effect on cattle. The wind affects the food reserves of animals and their hunting and defense strategies.
General causes
The great atmospheric layer is traversed by solar radiation that heats the ground, which, in turn, heats the air that surrounds it. Thus it turns out that this is not heated directly by the solar rays that pass through it, but indirectly, by the heating of the ground and of the aquatic surfaces. When air is heated, it also expands, like any gas, that is, it increases in volume, so it rises until its temperature equals that of the surrounding air or something else. Broadly speaking, the air masses go from the tropics to the equator (trade winds, which are constant, that is, they blow throughout the year), where they manage to rise so much due to their warming as latitude decreases (in the intertropical zone). as well as by the centrifugal force of the terrestrial rotation movement itself, which in turn gives rise to the thickness of the atmosphere in the equatorial zone being the greatest on the entire terrestrial surface. As they ascend, they cool down, and through the upper layers they return to the tropics, where they descend due to their greater weight (cold and dry air), which explains the presence of subtropical deserts and the high daily thermal amplitude of the deserts (in the In the Sahara it is common for temperatures of almost 50º during the day, due to the insolation and lack of clouds, to be contrasted with very low temperatures at night.Thus, in these desert areas, temperatures vary greatly from day to night at night. low amount of water and water vapor, which would contribute to a greater thermal regularity).
The first known scientific description of the wind is due to the Italian physicist Evangelista Torricelli: ...winds are produced by differences in air temperature, and therefore density, between two regions of the Earth.
Other forces that move or affect the wind are pressure gradient forces, the Coriolis effect, buoyancy and friction forces, and landforms. When there is a difference in density between two adjacent air masses, the air tends to flow from the regions of higher pressure to those of lower pressure. On a rotating planet, this airflow will be influenced, accelerated, elevated, or transformed by the Coriolis effect at any point on the Earth's surface. The belief that the Coriolis effect does not act at the equator is wrong: what happens is that the winds slow down as they approach the intertropical convergence zone, and this slowdown is automatically offset by a gain in height of the air in all the equatorial zone. In turn, this height gain gives rise to the formation of clouds of great vertical development and intense and prolonged rains, widely distributed in the intertropical convergence zone, especially in said equatorial zone. Superficial friction with the ground generates irregularities in these principles and affects the wind regime, such as the Föhn effect.
Globally speaking, the originating and predominant factor on a large scale is the difference in warming between some areas and others according to certain geographical and astronomical factors, as well as seasonal or temporal variations produced by the rotation and translation movements of the planet. When talking about the wind, reference is always made to the winds on the earth's surface up to a certain height, which varies according to latitude, relief and other factors. In turn, this superficial movement of the air, called wind, has a compensation in height that almost always follows a trajectory opposite to that of the true winds on the surface. Thus, a depression, a cyclone or an area of low pressure on the surface produced by the superficial heating of the air forces the hot air to rise and gives rise to a zone of high pressure in height where the cold and dry air descends towards the zones where the air came from on the surface: this is how cumulonimbus clouds, tornadoes, hurricanes, fronts and other meteorological phenomena are formed. A compensation in height to the direction of the winds are the jet streams that occur at high altitude and at high speed (). The extraordinary speed of these currents in height (about 250 km/h) in an approximate direction west - east is due to the low density of the air at the height where they occur. In effect, these winds offset the trade winds that blow superficially between Europe and South America across the Atlantic and also between Asia and North America in the same direction and with the same characteristics. As these jet streams have a height similar to that used by planes on their transatlantic flights, the difference between flying in one direction or the other can be a couple of hours or more on long hauls. On the other hand, the high speeds of these currents, which at low altitude could be catastrophic for airplanes, at an altitude of more than 10 km are not so problematic due to the low density of the air.
Winds are also defined as a system that uses the atmosphere to achieve a mechanical balance of forces, which makes it possible to break down and analyze its characteristics. It is very common to simplify the atmospheric motion equations by means of different wind components that, added together, give rise to the existing wind. The geostrophic wind component is the result of balancing the Coriolis force and the pressure gradient force. This wind flows perpendicular to the isobars, and it can be said that the effects of friction in mid-latitudes they are negligible for the upper layers of the atmosphere. Thermal wind is a wind that differentiates two levels that only exist in an atmosphere with horizontal temperature gradients or baroclinia. Gradient wind is similar to geostrophic but also includes the balance of centrifugal force.
Physical characteristics of winds
The systematic study of wind characteristics is very important for:
- dimensional structures of buildings such as silos, large galpones, elevated buildings, etc.
- design wind power generating fields.
- design protection of margins in reservoirs and mountain slopes in dams.
The measurement of the speed and direction of the wind is carried out with recording instruments called anemometers, which have two sensors: one to measure the speed and another to measure the direction of the wind. Measurements are recorded on anemographs.
For the measurements to be comparable with measurements made in other parts of the planet, the towers with the speed and direction sensors must obey strict regulations dictated by the WMO - World Meteorological Organization.
Speed of the winds
The oldest instrument for knowing the direction of the winds is the weather vane which, with the help of the wind rose, defines the origin of the winds, that is, the direction from which they blow. The windsock used at airports is usually large enough and visible to be observed from airplanes both during takeoff and, especially, when landing.
The speed, that is, the speed and direction of the winds, is measured with the anemometer, which usually registers said direction and speed over time. The intensity of the wind is ordered according to its speed using the Beaufort scale. This scale is divided into several sections according to their effects or damage caused, from calm air to category 5 hurricanes and tornadoes.
The record for the highest wind speed on the earth's surface is held by Mount Washington in New Hampshire (United States), with 231 miles per hour, that is, 372 km/h, recorded on the afternoon of April 12, 1934. The cause of this great speed of the wind is in the local configuration of the relief, which forms a kind of saddle from north to south that forces the west wind to concentrate on the pass as if it were a funnel. It is important to note that this enormous speed is only reached in a kind of sparse nozzle, being much less at a short distance from this point. All the mountain ranges of the planet have similar points, where the winds blow strongly due to the existence of passes, passes, hills or saddles where the passage of the wind is concentrated and accelerated. In Venezuela, the trans-Andean highway passes through a saddle of this type between the Mocotíes river basin and the Táchira depression and which has the very appropriate name of Páramo Zumbador due to the force of the wind.
Wind measurement
The direction of the wind is the cardinal point from which it originates and is measured with the weather vane. For example, the northerly wind obviously comes from the north and heads south. Windsocks are used at airports to indicate the direction of the wind and estimate the speed from the angle between the windsock and the wind. the ground. The weathervanes have the directions of the winds indicated at the bottom with the cardinal points and the intermediate points, thus forming what is known as the wind rose, which is used with a compass in the navigation mechanisms of boats for many centuries. Wind speed is measured with anemometers, directly by means of rotating blades or indirectly by pressure differences or ultrasonic transmission speed. Another type of anemometer is the pitot tube that determines the speed of the wind from the difference in pressure of a tube subjected to dynamic pressure and another to atmospheric pressure.
General circulation of winds
The movement of air in the troposphere, which is the most important for human beings, always has two components: the horizontal, which is the most important (hundreds and even thousands of km) and the vertical (10 km or more) that always compensates, with the rise or fall of the air, its horizontal movement. The example of tornadoes serves to identify the compensation process between the horizontal advance of the moving air and its ascent: the initial eddy of a tornado rotates at high speed, lifting and destroying houses and other objects, but as the wind rises, the twisting cone of the tornado widens, so its spin speed decreases. Said example of tornadoes is very useful because it has been possible to obtain great information, first hand, and to study well all the general processes that occur in any type of wind. But especially, the transformation of the linear movement of the surface wind into a rotating movement of vertical ascent of the same can be easily seen in any eddy or tornado and even in any cloud of vertical development such as a cumulonimbus or a hurricane: the size or extension varies but The process is the same.
And in types of winds that travel long distances, the same process occurs. Thus we have that the trade winds, which circulate between the tropics and the equator, travel long distances in a northeast-southwest direction in the northern hemisphere and in a southeast-northwest direction in the southern hemisphere. But when these winds arrive close to the equator, they rise inevitably, not so much because of the intertropical convergence, but because of the equatorial bulge, which is much more noticeable for reasons of density in the oceans than in the continents, and even more noticeable in the atmosphere than in the the oceans and when rising due to the centrifugal force of the terrestrial rotation movement, they produce clouds of vertical development and intense rains, with which their translation speed decreases rapidly. As the rising air cools and loses the moisture it brought with condensation and subsequent precipitation, we have cold, dry air. As very cold air is heavier, it will tend to descend towards the surface forming a kind of inclined plane that goes from the equator to the tropics, its direction being the opposite of that of the trade winds. This current of air or wind in the upper and middle zone of the troposphere goes down and deviates to the right until completing the cycle of the trade winds. We thus see that the principle of conservation of matter (and therefore, of energy) formulated by Lavoisier in the XVIII century It is perfectly fulfilled here and the trade winds are almost perfectly compensated by the high winds that were called counter trade winds, although this name has not been very successful. Numerous works that refer to the subject of contralisios deny their existence, perhaps because this return of dry and cold air is done without clouds, with which it is not possible to see their trajectory. But the experimental verification of the same can be seen in the lack of clouds in the sea of the Antilles: the high pressure caused by the return winds called contralisios gives rise to the descent of cold and dry air and the climates of the islands where this process occurs (Netherlands and Venezuelan Antilles, for example, with an annual rainfall in Aruba or Orchila of just over 100 mm) gives rise to an unusually dry climate, very well explained by Glenn T. Trewartha on dry coastal climates of the Caribbean of Colombia and Venezuela. The same process can be seen in the great deserts, where the nights are extremely cold and the days extremely hot, in which enormous daily thermal amplitudes of 30 and up to 40 °C can occur.
Types of winds
According to the scale or dimension of its journey, there are three types of winds: planetary winds, regional winds, and locals, although there are some types, such as the monsoons, which are more difficult to determine and which occupy variants within this simple classification.
The global winds, constant or planetary, are generated mainly as a consequence of the movement of the Earth's rotation, which causes uneven heating of the atmosphere by insolation and come from centers of action arranged in latitudinal strips of high and low pressures, that is, of anticyclones and depressions. These belts are arranged approximately in the equatorial, subtropical and polar latitudes (polar circles) and are responsible for transporting a truly enormous amount of energy. These winds are known as trades in intertropical latitudes and westerly winds in temperate zones.
Another type of planetary wind is the monsoon that affects Asia and the Indian Ocean and is generated by seasonal temperature differences between the continents and the sea. There are some authors who include monsoons as seasonal winds since they occur, in reverse, in summer and winter. During the summer, the continent (in this case, Asia) warms more than the Indian Ocean, resulting in a zone of continental low pressure, which attracts warm and humid winds from the Indian Ocean, which give rise to very heavy rainfall. intense because the Himalayas and others constitute a barrier to these winds and force the air to rise, producing orographic rains. During the winter, on the contrary, the ocean is warmer than the continent, therefore, the monsoons move from the continent towards the Indian Ocean where they bring cloudless skies and dry air, due to the low amount of moisture on the land continental. Monsoons also occur in the Midwest of the United States, but their effects are not as violent as in Asia, since there are no mountain ranges as high as the Himalayas that increase rainfall with their orographic effect (orographic rain).
Intertropical Convergence Zone
The intertropical convergence zone is a low pressure belt (Strahler points out that this belt has a pressure slightly below normal, usually between 1009 and 1013 mb —millibars—) and is determined by the movement of terrestrial rotation which generates what is known as terrestrial equatorial bulge, much more notorious, due to the different density, in the oceans than in the continents and even more notorious in the atmosphere than in the oceans. In the diagram of the planetary circulation of the winds, this greater bulge of the atmosphere can be seen in the equatorial zone (on the right of the image). That is why the thickness of the atmosphere is much greater in the intertropical zone (the troposphere reaches almost 20 km in height), while in the polar zones it is much thinner.
It is very important to take into account that when we talk about intertropical convergence we are referring to the surface winds since at a high altitude (almost at the limits of the troposphere in the equatorial zone) what exists is a divergence of the winds. This idea could be considered as a general proposition: to each zone of low pressure on the earth's surface there corresponds an anticyclonic zone in height. The low pressure zone at ground level is small, where the winds rotate and rise counterclockwise (from right to left), while at a certain height a much more extended high pressure zone forms, which gives us It gives a funnel shape with an almost flat crown, with or without a storm eye and asymmetrically, whose rotational movement stops when the atmospheric pressure on the surface becomes more homogeneous and the column of warm air stops rising. One speaks then of an occlusion process or an occluded front.
Subtropical Divergence Zones
They are areas of subsidence of cold air coming from high altitudes in the intertropical convergence zone, that is, from the equatorial strip, and which, in turn, give rise to the trade winds, which return towards the equator at low altitude, and to the west winds, which increase their speed as they also increase in latitude.
Polar convergence zones
They are areas of low pressure that attract winds from subtropical latitudes. These winds bring warmer and more humid air masses, moisture that they lose through condensation (rain, dew and frost) as they encounter cooler air with increasing latitude. This relative humidity is what supplies the ice caps of Greenland and Antarctica with frost ice.
Regional winds
They are determined by the distribution of lands and seas, as well as by the great continental reliefs. The monsoons can also be considered as regional winds, although their duration in time and their seasonal alternation make them more like planetary winds.
Local winds
Like other types of winds, local winds present a displacement of the air from areas of high pressure to areas of low pressure, determining the prevailing winds and the prevailing winds of a more or less wide area. Even so, it is necessary to take into account numerous local factors that influence or determine the characteristics of intensity and periodicity of air movements. These factors, difficult to simplify due to their multiplicity, are what allow us to speak of local winds, which are in many places more important than those of a general nature. These types of winds are the following:
- Marine and terrestrial brisas
- Valley breeze
- Mountain breeze
- Catabatic wind. Winds that descend from the heights to the bottom of the valleys produced by the slide to the ground of the cold air and dense from the elements of the highest relief. They appear continuously in the big glaciers, acquiring huge proportions in the ice cap of Greenland and Antarctica, where they blow at continuous speeds that exceed 200 km/h motivated by the absence of obstacles that slow down their acceleration.
- Anabotic wind. Winds rising from the lowest to the highest as the sun warms the relief.
Effects of winds
The wind acts as a transport agent, in fact, it intervenes in anemophilous pollination, in the displacement of the seeds.
It is also a powerful erosive agent, especially in areas with a dry or desert climate, where the grains of sand carried by the wind can lead to the transformation and even the denudation (that is, the complete removal) of the forms of the relief.
It also acts as a sedimentation agent, since when the wind slows down, it deposits the materials it transports. The sand forms accumulations called dunes, which move in the direction of the wind as the grains are carried from the side facing the wind (windward) to the side facing the wind (leeward). Although this process is present in arid climates, it is also frequent in other climates, for example in savannah climates, as occurs in the Orinoco basin, in the Llanos Bajos of Apure and Guárico states, where elongated dunes of about 20 m high that can reach more than 100 km in length. This landscape of dunes in a savannah climate, which has a dry season but annual rainfall of about 1,500 mm, constitutes an ecosystem that is practically unique in the world, which was declared a national park in Venezuela, under the name of Santos Luzardo National Park. In this park, gigantic sandy dunes, mighty rivers that gradually adapt their course to the layout of the dunes, herbaceous savannahs and gallery forests coexist.
Greater destructive effects
Wind is also a major destructive agent, especially in the case of tornadoes and major hurricanes. This destruction can be direct, as happened in 1940 with the destruction of the suspension bridge in Tacoma (Washington) or indirect, as happened with the hurricanes Hurricane Katrina in New Orleans (2005) and other nearby cities, in New York during Hurricane Sandy (2012) and in Houston with Hurricane Harvey in 2017. In these last three cases, the force of the wind caused enormous flooding, when the waves whipped inland, which dammed the enormous floods of the great Mississippi rivers in New Orleans and Hudson in New Orleans. New York, as well as the simultaneous floods of others of lesser flow. For this reason, there are people who suffer from ancrophobia, the fear of the wind that is caused by a traumatic experience with it.
Taking advantage of the winds
Natural ventilation
A type of housing in accordance with bioclimatic principles, that is, biology and climate, is the one that takes advantage of the environment to regulate the variation of the meteorological elements of the atmosphere in order to achieve a degree of ventilation, temperature and humidity that make the stay in said home more comfortable. It is about bioclimatic architecture that takes into account the glazing of the houses, which allows the greatest use of solar radiation during cold seasons and cross ventilation in hottest seasons.
Large windows that allow the natural ventilation of homes are a simple, natural and free way to make them more habitable and comfortable, especially in the regions of the intertropical zone, where the difference between the proper orientation of doors and windows with respect to the cardinal points, as well as the inclination of the roofs or roofs of each house, can mean a difference of more than 15 °C in the daily oscillation of the temperature with respect to the houses that ignore these characteristics.
Navigation
Wind propulsion has been an application of wind energy for navigation since the first civilizations (especially those that arose in the Mediterranean Sea) until the present time, when sailing vessels have been reduced to uses sports or recreation, with the exception of some school ships or special boats in shallow lagoons (the Albufera in Valencia would be a good example), where the force of the wind has been used from Muslim times to the present, in the cargo of the rice harvest to the places of processing of this cereal.
In sailing, knowledge and control of the wind is a fundamental factor for proper navigation. Thus, in marine language they receive different names and expressions depending on their strength, direction or origin.
Eolionymy
When something occurs regularly in an area, it is normal for the place to be given its own name. The case of the winds is not an exception, in this way the winds are named, as has already been said, by their origin (for example, the north wind) or by their characteristics.
Importance
It is impossible to underestimate the importance that winds have for the life of animals and plants, for the restoration of balance in the atmosphere and, logically, for the production of the hydrological cycle. That is why, just as can be said in relation to the hydrological cycle, the wind constitutes one of the essential factors that explain life on the earth's surface. Without the existence of the winds, life for animals and plants would be impossible due to the fundamental role of the wind in the hydrological cycle.