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Encyclopedia > Atmospheric circulation

Atmospheric circulation is the large-scale movement of air, and the means (together with the smaller ocean circulation) by which heat is distributed on the surface of the Earth. An ocean current is any more or less permanent or continuous, directed movement of ocean water that flows in one of the Earths oceans. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... This article is about Earth as a planet. ...


The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant. However, individual weather systems - midlatitude depressions, or tropical convective cells - occur "randomly", and it is accepted that weather cannot be predicted beyond a fairly short limit: perhaps a month in theory, or (currently) about ten days in practice (see Chaos theory and Butterfly effect). Nonetheless, the average of these systems - the climate - is stable over longer periods of time. For other uses, see Chaos Theory (disambiguation). ... Point attractors in 2D phase space. ...

An idealised view of three large circulation cells.
An idealised view of three large circulation cells.

Contents

Image File history File links atmospheric circulation diagram, showing the Hadley cell, the Ferrel cell, the Polar cell, and the various upwelling and subsidence zones between them. ... Image File history File links atmospheric circulation diagram, showing the Hadley cell, the Ferrel cell, the Polar cell, and the various upwelling and subsidence zones between them. ...

Latitudinal circulation features

The wind belts and the girdling the planet are steered by three cells: the Hadley cell, the Ferrel cell, and the Polar cell (the interpretation of the latter two is complex). Note that there is not one discrete Hadley cell, for instance, but several within the equatorial zone which shift, merge, and decouple in a complicated process over time. For descriptive purposes, however, they are generally referred to in the singular. Vertical velocity at 500 hPa, July average. ... The Ferrel cell is usually shown between the Hadley and Polar cells, e. ... World map showing the equator in red For other uses, see Equator (disambiguation). ...

Vertical velocity at 500 hPa, July average. Ascent (negative values) is concentrated close to the solar equator; descent (positive values) is more diffuse
Vertical velocity at 500 hPa, July average. Ascent (negative values) is concentrated close to the solar equator; descent (positive values) is more diffuse

Image File history File links Omega-500-july-era40-1979. ... Image File history File links Omega-500-july-era40-1979. ...

Hadley cell

Main article: Hadley cell

The Hadley cell mechanism is well understood. The atmospheric circulation pattern that George Hadley described to provide an explanation for the trade winds matches observations very well. It is a closed circulation loop, which begins at the equator with warm, moist air lifted aloft in equatorial low pressure areas to the tropopause and carried poleward. At about 30°N/S latitude, it descends in a high pressure area. Some of the descending air travels equatorially along the surface, closing the loop of the Hadley cell and creating the Trade Winds. Vertical velocity at 500 hPa, July average. ... George Hadley (1685-1768) was an English lawyer and amateur meteorologist who proposed the atmospheric mechanism by which the Trade Winds were sustained. ... A large low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that nature abhors a vacuum. ... The tropopause is between the troposphere and the stratosphere. ... It has been suggested that this article or section be merged into Anticyclone. ... Image:Atmospheric circulatlion. ...


Though the Hadley cell is described as lying on the equator, it should be noted that it is more accurate to describe it as following the sun’s zenith point, or what is termed the "thermal equator," which undergoes a semiannual north-south migration. In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ... Climate map showing the thermal equator The thermal equator is a belt encircling the Earth, defined by the set of locations having the highest mean annual temperature at each longitude around the globe. ...


Polar cell

Main article: Polar vortex

The Polar cell is likewise a simple system. Though cool and dry relative to equatorial air, air masses at the 60th parallel are still sufficiently warm and moist to undergo convection and drive a thermal loop. Air circulates within the troposphere, limited vertically by the tropopause at about 8 km. Warm air rises at lower latitudes and moves poleward through the upper troposphere at both the north and south poles. When the air reaches the polar areas, it has cooled considerably, and descends as a cold, dry high pressure area, moving away from the pole along the surface but twisting westward as a result of the Coriolis effect to produce the Polar easterlies. The polar vortex is a persistent, large-scale cyclone located near the Earths poles, in the middle and upper troposphere and the stratosphere. ... Convection in the most general terms refers to the movement of currents within fluids (i. ... A thermal loop is a movement of air driven by warm air rising at one end of the loop, and cool air descending at the other end, creating a constantly moving loop of air. ... Atmosphere diagram showing the mesosphere and other layers. ... In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ... The polar easterlies are the prevailing winds that blow from the high-pressure areas of the polar highs at the north and south poles towards the low-pressure areas of the polar fronts at around 60 degrees latitude (north and south). ...


The outflow from the Polar cell creates harmonic waves in the atmosphere known as Rossby waves. These ultra-long waves play an important role in determining the path of the jet stream, which travels within the transitional zone between the tropopause and the Ferrel cell. By acting as a heat sink, the Polar cell also balances the Hadley cell in the Earth’s energy equation. This article is about the components of sound. ... Rossby (or planetary) waves are large-scale motions in the ocean or atmosphere whose restoring force is the variation in Coriolis effect with latitude. ... For other uses, see jet stream (disambiguation). ... The tropopause is between the troposphere and the stratosphere. ... The Ferrel cell is usually shown between the Hadley and Polar cells, e. ... This article is about the substance or device. ...


It can be argued that the Polar cell is the primary weathermaker for regions above the middle northern latitudes. While Canadians and Europeans may have to deal with occasional heavy summer storms, there is nothing like a winter visit from a Siberian high to give one a true appreciation of real cold. In fact, it is the polar high which is responsible for generating the coldest temperature recorded on Earth: -89.2°C at Vostok II Station in 1983 in Antarctica. This article is about Siberia as a whole. ...


The Hadley cell and the Polar cell are similar in that they are thermally direct; in other words, they exist as a direct consequence of surface temperatures; their thermal characteristics override the effects of weather in their domain. The sheer volume of energy the Hadley cell transports, and the depth of the heat sink that is the Polar cell, ensures that the effects of transient weather phenomena are not only not felt by the system as a whole, but — except under unusual circumstances — are not even permitted to form. The endless chain of passing highs and lows which is part of everyday life for mid-latitude dwellers is unknown above the 60th and below the 30th parallels. This article is about the substance or device. ...


These atmospheric features are also stable, so even though they may strengthen or weaken regionally or over time, they do not vanish entirely.


Ferrel cell

The Ferrel cell, theorized by William Ferrel (1817-1891), is a secondary circulation feature, dependent for its existence upon the Hadley cell and the Polar cell. It behaves much as an atmospheric ball bearing between the Hadley cell and the Polar cell, and comes about as a result of the eddy circulations (the high and low pressure areas) of the midlatitudes. For this reason it is sometimes known as the "zone of mixing." At its southern extent (in the Northern hemisphere), it overrides the Hadley cell, and at its northern extent, it overrides the Polar cell. Just as the Trade Winds can be found below the Hadley cell, the Westerlies can be found beneath the Ferrel cell. Thus, strong high pressure areas which divert the prevailing westerlies, such as a Siberian high (which could be considered an extension of the Arctic high), could be said to override the Ferrel cell, making it discontinuous. William Ferrel This page is about the meteorologist; for the comedian, see Will Ferrell. ... In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. ... The Westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. ... The Siberian High is a massive collection of cold or very cold dry air that accumulates on the Eurasian terrain for much of the year. ...


While the Hadley and Polar cells are truly closed loops, the Ferrel cell is not, and the telling point is in the Westerlies, which are more formally known as "the Prevailing Westerlies." While the Trade Winds and the Polar Easterlies have nothing over which to prevail, their parent circulation cells having taken care of any competition they might have to face, the Westerlies are at the mercy of passing weather systems. While upper-level winds are essentially westerly, surface winds can vary sharply and abruptly in direction. A low passing to the north or a high passing to the south (from a Northern Hemisphere frame of reference) maintains or even accelerates a westerly flow; the local passage of a cold front may change that in a matter of minutes, and frequently does. A strong high passing to the north may bring easterly winds for days. The Westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. ... This article or section is in need of attention from an expert on the subject. ...


The base of the Ferrel cell is characterized by the movement of air masses, and the location of these air masses is influenced in part by the location of the jet stream, which acts as a collector for the air carried aloft by surface lows (a look at a weather map will show that surface lows follow the jet stream). The overall movement of surface air is from the 30th latitude to the 60th. However, the upper flow of the Ferrel cell is not well defined. This is in part because it is intermediary between the Hadley and Polar cells, with neither a strong heat source nor a strong cold source causes convection, and in part because of the effects on the upper atmosphere of surface eddies, which act as destabilizing influences. For other uses, see jet stream (disambiguation). ...


Longitudinal circulation features

While the Hadley, Ferrel, and Polar cells are major players in global heat transport, they do not act alone. Disparities in temperature also drive a set of longitudinal circulation cells, and the overall atmospheric motion is known as the zonal overturning circulation.


Latitudinal circulation is the consequence of the fact that incident solar radiation per unit area is highest at the heat equator, and decreases as the latitude increases, reaching its minimum at the poles. Longitudinal circulation, on the other hand, comes about because water has a higher specific heat capacity than land and thereby absorbs and releases heat less readily than land. Even at microscales, this effect is noticeable; it is what brings the sea breeze, air cooled by the water, ashore in the day, and carries the land breeze, air cooled by contact with the ground, out to sea during the night.


On a larger scale, this effect ceases to be diurnal (daily), and instead is seasonal or even decadal in its effects. Warm air rises over the equatorial, continental, and western Pacific Ocean regions, flows eastward or westward, depending on its location, when it reaches the tropopause, and subsides in the Atlantic and Indian Oceans, and in the eastern Pacific. For other senses of this word, see decade (disambiguation). ... This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Animated, colour-coded map showing the various continents. ... A road destroyed by subsidence and shear. ... Atlantic and North Atlantic redirect here. ... Pacific redirects here. ...


The Pacific Ocean cell plays a particularly important role in Earth's weather. This entirely ocean-based cell comes about as the result of a marked difference in the surface temperatures of the western and eastern Pacific. Under ordinary circumstances, the western Pacific waters are warm and the eastern waters are cool. The process begins when strong convective activity over equatorial East Asia and subsiding cool air off South America's west coast creates a wind pattern which pushes Pacific water westward and piles it up in the western Pacific. (Water levels in the western Pacific are about 60 cm higher than in the eastern Pacific, a difference due entirely to the force of moving air.)[1][2][3] For the geological process, see Weathering or Erosion. ...


Walker circulation

The Pacific cell is of such importance that it has been named the Walker circulation after Sir Gilbert Walker, an early-20th-century director of British observatories in India, who sought a means of predicting when the monsoon winds would fail. While he was never successful in doing so, his work led him to the discovery of an indisputable link between periodic pressure variations in the Indian Ocean and the Pacific, which he termed the "Southern Oscillation." Sir Gilbert Thomas Walker (1868-1958) was an English physicist and statistician of the 20th century. ... For other uses, see Monsoon (disambiguation). ... The Southern Oscillation refers to an oscillation in air pressure between the southeastern and southwestern Pacific waters. ...


The movement of air in the Walker circulation affects the loops on either side. Under "normal" circumstances, the weather behaves as expected. But every few years, the winters become unusually warm or unusually cold, or the frequency of hurricanes increases or decreases, and the pattern sets in for an indeterminate period.



The behavior of the Walker cell is the key to the riddle, and leads to an understanding of the El Niño (more accurately, ENSO or El Niño - Southern Oscillation) phenomenon. Chart of ocean surface temperature anomaly [°C] during the last strong El Niño in December 1997 El Niño and La Niña (also written in English as El Nino and La Nina) are major temperature fluctuations in surface waters of the tropical Eastern Pacific Ocean. ...


If convective activity slows in the Western Pacific for some reason (this reason is not currently known), the climate dominoes next to it begin to topple. First, the upper-level westerly winds fail. This cuts off the source of cool subsiding air, and therefore the surface Easterlies cease.


The consequence of this is twofold. In the eastern Pacific, warm water surges in from the west since there is no longer a surface wind to constrain it. This and the corresponding effects of the Southern Oscillation result in long-term unseasonable temperatures and precipitation patterns in North and South America, Australia, and Southeast Africa, and disruption of ocean currents.


Meanwhile in the Atlantic, high-level, fast-blowing Westerlies which would ordinarily be blocked by the Walker circulation and unable to reach such intensities, form. These winds tear apart the tops of nascent hurricanes and greatly diminish the number which are able to reach full strength. This article is about weather phenomena. ...


El Niño - Southern Oscillation

El Niño and La Niña are two opposite surface temperature anomalies in the Southern Pacific, which heavily influence the weather on a large scale. In the case of El Niño warm water aproaches the coasts of South America which results in blocking the upwelling of nutrient-rich deep water. This has serious impacts on the fish populations. This article is about the global coupled ocean-atmosphere phenomenon. ...


In the La Niña case, the convective cell over the western Pacific strengthens inordinately, resulting in colder than normal winters in North America, and a more robust cyclone season in South-East Asia and Eastern Australia. There is increased upwelling of deep cold ocean waters and more intense uprise of surface air near South America, resulting in increasing numbers of drought occurrence, although it is often argued that fishermen reap benefits from the more nutrient-filled eastern Pacific waters.


The neutral part of the cycle - the "normal" component - has been referred to humorously by some as "La Nada", which means "the nothing" in Spanish.


External links

  • Animation showing global cloud circulation for one month based on weather satellite images

References

  1. ^ Envisat watches for La Nina. BNSC (2006-03-03). Retrieved on 2007-07-26.
  2. ^ The Tropical Atmosphere Ocean Array: Gathering Data to Predict El Niño. Celebrating 200 Years. NOAA (2007-01-08). Retrieved on 2007-07-26.
  3. ^ Ocean Surface Topography. Oceanography 101. JPL (2006-07-05). Retrieved on 2007-07-26.ANNUAL SEA LEVEL DATA SUMMARY REPORT JULY 2005 - JUNE 2006 (pdf). THE AUSTRALIAN BASELINE SEA LEVEL MONITORING PROJECT. Bureau of Meteorology. Retrieved on 2007-07-26.
Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 62nd day of the year (63rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 8th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 186th day of the year (187th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... The currents of the North Pacific Gyre The North Pacific Gyre (also known as North Pacific Subtropical Gyre) is a clockwise-swirling vortex of ocean currents comprising most of the northern Pacific Ocean. ... The North Equatorial Current is a significant Pacific and Atlantic Ocean current that flows east-to-west between the equator and 10° north. ... The Kuroshio Current is an ocean current found in the western Pacific Ocean off the east coast of Taiwan and flowing northeastward past Japan, where it merges with the easterly drift of the North Pacific Current. ... The North Pacific Current The North Pacific Current (sometimes referred to as the North Pacific Drift) is a slow warm water current that flows west-to-east between 40 and 50 degrees north in the Pacific Ocean. ... The California Current is a Pacific Ocean current that moves south along the western coast of North America, beginning off southern British Columbia, and ending off southern Baja California. ... The South Equatorial Current is a significant Pacific Ocean current that flows east-to-west between the equator and 10 degrees south. ... East Australian Current on August 17, 2005 The East Australian Current (EAC) flows north-to-south along the east coast of Australia. ... The Antarctic Circumpolar Current (ACC) is an ocean current that flows from west to east around Antarctica. ... ... For the novel by Jean Rhys, see Wide Sargasso Sea. ... The North Equatorial Current is a significant Pacific and Atlantic Ocean current that flows east-to-west between the equator and 10° north. ... For the album by Ocean Colour Scene, see North Atlantic Drift (album) The Gulf Stream is orange and yellow in this representation of water temperatures of the Atlantic. ... Schematic of the worlds ocean currents. ... The Canary Current branches south from the North Atlantic Current and flows toward the South West about as far as Senegal where it turns West. ... The South Equatorial Current is a significant Pacific Ocean current that flows east-to-west between the equator and 10 degrees south. ... The Brazil Current is a warm water current that flows southward along the Brazilian south coast to the mouth of the River Plate. ... The Antarctic Circumpolar Current (ACC) is an ocean current that flows from west to east around Antarctica. ... The frigid waters of the north-flowing Benguela current move from the Southern Ocean that surrounds Antarctica along the west coast of Africa as far as Angola. ... The South Equatorial Current is a significant Pacific Ocean current that flows east-to-west between the equator and 10 degrees south. ... The Agulhas Current is the Western Boundary Current of the South-West Indian Ocean and is part of the westward-flowing South Equatorial Current. ... The Antarctic Circumpolar Current (ACC) is an ocean current that flows from west to east around Antarctica. ... The Antarctic Circumpolar Current (ACC) is an ocean current that flows from west to east around Antarctica. ... Ocean currents (1911) Ocean currents (1943) An ocean current is any more or less continuous, directed movement of ocean water that flows in one of the Earths oceans. ... In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ... Closely related to the Ekman spiral, where winds blowing up and down coastal regions cause a seaward flow of surface water (perpendicular to the flow of wind), which creates the upwelling of deep nutrient rich sea water. ... A simplified summary of the path of the Thermohaline Circulation. ... A turtle is trapped in a ghost net, an abandoned fishing net Marine debris usually applies to floating waste such as bottles, cans, styrofoam, cruise ship waste, offshore oil and gas exploration and production facilities pollution, and fishing paraphanalia from professional and recreational boaters. ... The North Pacific Gyre is one of five major oceanic gyres The Great Pacific Garbage Patch is an area of marine debris in the North Pacific Gyre, and is also known as the Plastic soup, the Eastern Garbage Patch, and the Pacific Trash Vortex. ...

  Results from FactBites:
 
Atmospheric circulation (667 words)
Atmospheric circulation is the large-scale movement of air by which heat is distributed on the surface of the Earth.
Hadley cell — The major driving force of atmospheric circulation in the tropical regions is solar heating.
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Coriolis effect causes global circulation to be divided into three cells of circulation in the northern hemisphere and three cells of circulation in the southern hemisphere with their boundaries generally at the equator and at 30°N and 60°N latitude and at 30°S and 60°S latitude.
In the southern hemisphere, cyclonic circulation is clockwise.
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