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Subsidence (atmosphere)
In meteorology, subsidence is the downward movement of an air parcel as it cools and becomes denser. By contrast, warm air becomes less dense and moves upwards (atmospheric convection). Atmospheric subsidence generally creates a high-pressure area as more air moves into the same space: the polar highs are areas of almost constant subsidence, as are the horse latitudes, and the areas of subsidence are the sources of much of the prevailing winds in the Earth's atmosphere. Subsidence also causes many smaller-scale weather phenomena, such as morning fog; on the other hand, its absence may cause air stagnation. An extreme form of subsidence is a '' downburst'', which can result in damage similar to that produced by a tornado. A milder form of subsidence is referred to as '' downdraft''. Atmospheric pressure and atmospheric subsidence The Dosen barometer (pictured) clearly relates high pressure with fine weather, as seen in its dial. This is because high pressure zones ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth's Atmosphere
The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weather features such as clouds and hazes), all retained by Earth's gravity. The atmosphere serves as a protective buffer between the Earth's surface and outer space, shields the surface from most meteoroids and ultraviolet solar radiation, keeps it warm and reduces diurnal temperature variation (temperature extremes between day and night) through heat retention (greenhouse effect), redistributes heat and moisture among different regions via air currents, and provides the chemical and climate conditions allowing life to exist and evolve on Earth. By mole fraction (i.e., by quantity of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other trace gases (see Composition below ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Convection
Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow. Convective flow may be Transient state, transient (such as when a Multiphasic liquid, multiphase mixture of oil and water separates) or steady state (see convection cell). The convection may be due to Gravity, gravitational, Electromagnetism, electromagnetic or Fictitious force, fictitious body forces. Convection (heat transfer), Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its Earth's mantle, mantle. Discrete convective cells in the atmosphere can be identified by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diathermancy
Diathermancy (from "dia" ''through'' and "thermē" ''heat'') is the property of some fluids that allows rays of light through them without itself being heated. A diathermanous substance is thus " permeable" by heat. Diathermancy was first described by German physicist and chemist Heinrich Gustav Magnus in the 1800s.Magnus wrote initially four papers on Diathermanc/ref> Air ''is'' diathermanous; therefore atmospheric air ''is not'' heated by sunshine. Atmospheric air is heated by long-wave thermal radiation emitted by soil, and especially, by water on the Earth's surface. Water ''is not'' diathermanous, and it ''is'' heated directly by sunshine. Atmospheric heating from oceanic waters Atmospheric heat comes from long-wave radiation from the soil and, mostly, from the water surface (oceans, lakes, rivers), because water is a not diathermanous body and covers three quarters of Earth's surface. Diathermancy cause subsidence above damp or water surfaces. That is because these a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Downdraft
In meteorology, an updraft (British English: ''up-draught'') is a small-scale current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that move vertically. A mass of warm air will typically be less dense than the surrounding region, and so will rise until it reaches air that is either warmer or less dense than itself. The converse will occur for a mass of cool air, and is known as subsidence. This movement of large volumes of air, especially when regions of hot, wet air rise, can create large clouds, and is the central source of thunderstorms. Drafts can also be caused by low or high pressure regions. A low pressure region will attract air from the surrounding area, which will move towards the center and then rise, creating an updraft. A high pressure region will attract air from the surrounding area, which will move towards the center and sink, spawning a downdraft. Updrafts and downdrafts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tornado
A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Tornadoes come in many shapes and sizes, and they are often (but not always) visible in the form of a funnel cloud, condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than , are about across, and travel several kilometers (a few miles) before dissipating. The Tornado records#Highest winds observed in a tornado, most extreme tornadoes can attain wind speeds of mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Downburst
In meteorology, a downburst is a strong downward and outward gushing wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the area of impact at surface level. It originates under deep, moist convective conditions like cumulus congestus or cumulonimbus. Capable of producing damaging winds, it may sometimes be confused with a tornado, where high-velocity winds circle a central area, and air moves inward and upward. These usually last for seconds to minutes. Downbursts are particularly strong downdrafts within thunderstorms (or deep, moist convection as sometimes downbursts emanate from cumulonimbus or even cumulus congestus clouds that are not producing lightning). Downbursts are most often created by an area of significantly precipitation-cooled air that, after reaching the surface ( subsiding), spreads out in all directions producing strong winds. Dry downbursts are associated with thunderstorms that ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Air Stagnation
Air stagnation is a meteorological condition that occurs when there is a lack of atmospheric movement, leading to the accumulation of pollutants and particles that can decline the air quality in a particular region. This condition typically correlates with air pollution and poor air quality due to the possible health risks it can cause to humans and the environment. Due to light winds and lack of precipitation, pollutants cannot be cleared from the air, either gaseous (such as ozone) or particulate (such as soot or dust). Causes Typically air stagnation events develop under warm high-pressure systems, where conditions are stagnant and there is little vertical and horizontal air movement. When there is a stable atmospheric environment, pollutants are accumulated in areas near the surface. These pollutants include both gaseous and particulate matter such as ground-level O3 and PM2.5. Ground-level ozone and particulate matter originate from different sources and human activities ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere of Earth, atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature, precipitation, and other atmospheric conditions, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, "weather" is generally understood to mean the weather of Earth. Weather is driven by atmospheric pressure, air pressure, temperature, and moisture differences between one place and another. These differences can occur due to the effect of Sun angle on climate, Sun's angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prevailing Wind
In meteorology, prevailing wind in a region of the Earth's surface is a surface wind that blows predominantly from a particular direction. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface at any given time. A region's prevailing and dominant winds are the result of global patterns of movement in the Earth's atmosphere. In general, winds are predominantly easterly at low latitudes globally. In the mid-latitudes, westerly winds are dominant, and their strength is largely determined by the polar cyclone. In areas where winds tend to be light, the sea breeze-land breeze cycle (powered by differential solar heating and night cooling of sea and land) is the most important cause of the prevailing wind. In areas which have variable terrain, mountain and valley breezes dominate the wind pattern. Highly elevated surfaces can induce a thermal low, which then augments the environmental wind flow. Wind direction a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horse Latitudes
The horse latitudes are the latitudes about 30 degrees north and south of the Equator. They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as subtropical ridges or highs. It is a high-pressure area at the divergence of trade winds and the westerlies. Etymology A likely and documented explanation is that the term is derived from the "dead horse" ritual of seamen (see Beating a dead horse). In this practice, the seaman paraded a straw-stuffed effigy of a horse around the deck before throwing it overboard. Seamen were paid partly in advance before a long voyage, and they frequently spent their pay all at once, resulting in a period of time without income. This period was called the "dead horse" time, and it usually lasted a month or two. The seaman's ceremony was to celebrate having worked off the "dead horse" debt. As west-bound shipping from Europe usually reached the subtropics at about the time the "dead horse" was wo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
