atmospheric phenomena
Contenido
La dinámica atmosférica integra el conjunto de procesos físicos o meteorológicos que se producen en el seno de la atmósfera terrestre. Aunque la Tierra no es el único planeta con atmósfera haremos referencia aquí solamente a los procesos atmosféricos terrestres. El motor de todos los procesos atmosféricos terrestres se deriva de la radiación solar recibida por nuestro planeta de acuerdo a su movimiento de traslación y, sobre todo, al movimiento de rotación terrestre, y los cambios que origina en su seno, que son:.
Todos los procesos meteorológicos y bioquímicos de la atmósfera (y de los océanos) tienen un origen común: el calentamiento de nuestro planeta debido a los rayos solares. También algunos procesos geológicos internos pueden intervenir de alguna manera en el calentamiento o enfriamiento de la atmósfera, pero sus efectos son casi insignificantes a escala global, aunque localmente pueden tener cierta relevancia. Este calentamiento se realiza siempre hacia arriba, es decir, a partir de la superficie terrestre y, sobre todo, a partir de la superficie acuática. La razón está en la compresibilidad del aire: el aire se comprime debido a su propio peso y, por ende, la mayor presión se obtiene en la superficie de nuestro planeta. Una masa de aire comprimido puede calentarse en mucho mayor grado que una que se encuentre a menor presión, como se ha indicado en la imagen que explica el inflado de las ruedas de una bicicleta. El valor de este calentamiento se obtiene midiendo la temperatura atmosférica. Así pues, este calentamiento es, en su mayor parte, indirecto, porque gran parte de la radiación solar atraviesa el aire sin calentarlo hasta llegar a las capas inferiores en contacto con la superficie terrestre las cuales se calientan debido al calor reflejado por la superficie terrestre y, especialmente, marina. Dicho en otros términos, los rayos solares atraviesan casi toda la atmósfera sin calentarla significativamente, debido al fenómeno llamado diatermancia, que implica que el aire casi no absorbe el calor de los rayos solares incidentes, es decir, los procedentes directamente del Sol. Pero la superficie terrestre y oceánica reenvían hacia la atmósfera una radiación infrarroja, lo que se conoce como calor oscuro (rayos infrarrojos o rayos de calor, que son invisibles por el ojo humano). Los rayos infrarrojos sí calientan el aire por ser de onda larga y este proceso resulta favorecido por la mayor presión de la atmósfera al nivel de la superficie terrestre: como ya se ha visto, el aire comprimido puede atrapar mayor energía calórica que el aire a menor presión.
Diathermancy
The property of air to be crossed by solar rays almost without being heated by solar radiation is called diathermancy. This term should not be confused with diathermy, which is the medical treatment of various conditions with the use of heat radiation (infrared) by electrical or electromagnetic means. In English, the term diathermancy is used with the same meaning as developed here, and diathermanous refers to those bodies that are transparent to thermal radiation, that is, they allow the solar rays (visible spectrum) to pass through them directly without heating up perceptibly.
However, the superficial layer of air, in contact with both the solid and liquid surface of our planet, which is the one with the highest density because it supports the greatest weight of the atmosphere, absorbs a large amount of the heat reflected by said Earth's surface, so in this case, it is no longer diathermous, at least a short distance above the ground. What happens is that the heat reflected by the Earth's surface is made up of infrared rays (which is called dark heat because infrared rays cannot be seen) and their wavelength is very long (much longer than the visible rays of red light) and these do manage to heat the air, which rises automatically, thereby cooling rapidly until it reaches, at a certain height, the same temperature as the surrounding air, so its upward movement also automatically ceases. The process is reversed during much of the night and day, when the air at a certain height decreases its temperature due to nocturnal irradiation and descends accordingly. This means that the heating of the atmosphere by the sun's rays always brings a considerable time lag of about 12 hours in the equatorial zone to several days in the temperate and polar zones. This lag or delay is what determines the phenomena of subsidence and convection that, in turn, mark days of rain or dry weather.
Greenhouse effect
Because the entire atmosphere acts as if it were a single gas, there are no greenhouse gases or non-greenhouse gases. Thus, the greenhouse effect is the way in which the entire atmosphere, especially in the first km of height from the Earth's surface, protects our planet from the bombardment produced by aerolites (the so-called shooting stars show their incandescence due to friction with the air in the atmosphere) and by ultraviolet rays, mostly absorbed in the upper layers of the atmosphere. The protective effect of the atmosphere is similar to that of the transparent roof of a greenhouse, which allows light to pass through, but not other harmful effects for the plants, whose growth (water, light and nutrients) is always controlled in order to have optimal results. And as we see in the epiphytic plants on the power lines (photo taken about 15 km west of San Juan de los Morros in Venezuela), some plants only need rain and air to grow and survive: the rain and the water that forms the clouds absorb carbon dioxide from the air to form carbonic acid and water, discarding part of the oxygen that becomes the source of life for men and animals.
In turn, with photosynthesis, increasingly more complex molecules are achieved until we reach glucose, which would be the beginning of all the biomass that exists on our planet, according to the following formula:
according to which plants, through photosynthesis, can transform carbonic acid in the atmosphere into glucose, plus free oxygen.
Photosynthesis is what explains the fact that the long azoic (lifeless) era ended with the appearance of the first plants and, much later, animals appeared, when the plants regenerated the formation of free oxygen through this process of photosynthesis.
The greenhouse effect is therefore an effect produced by all the gases that make up the air and not just carbon dioxide and water vapor. Precisely, the best proof that all the gases that make up the atmosphere produce the greenhouse effect is the scarcity (percentage speaking) of carbon dioxide and water vapor. And the scarcity of carbon dioxide is explained, in turn, by being the gas that plants use to live and feed themselves. The same can be said of water vapor and the water itself that forms clouds.
atmospheric temperature
As has already been said, solar radiation is the initial engine of all atmospheric processes. But since this radiation is not uniform in space or time, areas arise that warm or cool more than others and these differences translate into differences in the unequal heating of the Earth's atmosphere, which are of fundamental importance in the study of geography and in the habitable conditions for plants, animals and human beings. The differences in air heating are known by measuring atmospheric temperature.
atmospheric pressure
Indirect heating of the air causes it to increase in volume and, therefore, to decrease its density. This density at a certain level is known as atmospheric pressure, a value measured with the mercury or aneroid barometer, a device developed based on Torricelli's initial experiment. With this device, the weight of a column of air in a certain place is measured, comparing it with the weight it should have under normal conditions. In summary, the indirect heating of the air by insolation generates a certain atmospheric pressure (the higher the temperature, the lower the atmospheric pressure) because the air expands, rises and, therefore, weighs less, that is, its pressure decreases. Differences in atmospheric pressure determine the production of winds that go from areas of higher pressure to those of lower pressure.
Winds
The movements of air within the atmosphere are called winds. Winds always have two components, one horizontal and one vertical, and both components compensate each other, at different scales, almost perfectly.
Solar heating of the atmosphere is not uniform, so there are colder areas and therefore higher pressure (anticyclones) and warmer areas where the pressure is lower (cyclones or depressions). As the air in cyclones or depressions tends to rise, the vacuum they leave is replaced by air from high pressure areas or anticyclones, thus giving rise to winds, which constitute one of the fundamental processes of atmospheric dynamics, as they are responsible for an enormous transfer of energy within the atmosphere.
Humidity
Air humidity is the amount of water vapor present in the Earth's atmosphere. Steam comes from the evaporation of water in the seas and oceans, in rivers, lakes, and from the transpiration of living beings, especially plants. It can be absolute (grams per cubic meter, for example) and relative (which is the percentage of the maximum humidity value or saturation point that the air has at a given time). Thus, a humidity of 25%, for example, would be a very low humidity, while a humidity close to 100% would be saturated and rapid condensation "Condensation (physical)") could begin to occur, and therefore, to form rain and other forms of precipitation, depending on the temperature. This means that the same absolute humidity will correspond to a lower relative humidity if the air temperature is high, and a higher relative humidity if the temperature is low.
Precipitation
Rainfall, just like winds, constitutes thermodynamic processes in the atmosphere that form a very important part of the hydrological cycle in nature. The processes involved in the hydrological cycle are:
In summary, rains give rise to a more equitable distribution (temporally and spatially) of the heat previously received by the Earth's surface from solar radiation.