From: Richard Eastman <richardeastmanyakima@q.com>
Date: Thu, Aug 19, 2010 at 5:39 AM
Subject: [bangla-vision] progress notes and partial draft of an important article
To:
Russia Drought Signals Higher Feed Costs For Livestock Producers
Despite an outlook for record U.S. corn and soybean harvests in 2010, crop prices will be higher than previously forecast because of stronger exports and tighter stockpiles, according to U.S. Department of Agriculture reports released today.
Beef and pork prices, already climbing much of this year, may get more expensive as higher feed costs are passed along, said Dan Basse, president of AgResource Co.
Additionally, the wide grain price swings, fueled by market skittishness over the Russian drought, are sure to continue, Basse said.
"The Russian drought has changed the landscape of American agriculture for the next 18 months," Basse said today during a press briefing held at Chicago-based CME Group's trading floor following the release of the USDA reports.
"Things are going to get spicier," Basse said. "We'll have big harvests, big crops and big demand. There will be plenty of volatility in the months to come."
Record harvests ahead amid favorable weather
Thanks to early planting and abundant rainfall across much of the Midwest, farmers are expected to reap a corn harvest of 13.365 billion bushels, up 1.9 percent from 2009 and an all-time high, the USDA said today.
The soybean harvest is projected at 3.433 billion bushels, up 2.2 percent from last year and also an all-time high.
Still, corn, soybean and wheat futures in Chicago surged today after the USDA cut its projection for Russia's wheat crop by 15 percent, citing "extreme drought and record heat" during July and early August. The USDA also hiked estimated U.S. exports and trimmed stocks.
Russia is now expected to harvest 45 million metric tons of wheat in the 2010-11 marketing year, down from 53 million metric tons in a July forecast.
The drought has also hit other major wheat-growing countries in that region, including Kazakhstan, whose projected harvest was lowered 21 percent, to 11.5 million metric tons.
The USDA's global wheat production estimates "were kind of breathtaking," said Jerry Gidel, an analyst with North American Risk Management Services Inc., who also spoke at the CME briefing.
USDA numbers "really show Russia has an amazingly poor wheat crop," Gidel said. "But in the U.S., we will have plenty of grain available for others. It's very important we continue to have good crops in the U.S."
Worldwide, wheat stocks next year are expected to drop 6.6 percent, to 174.8 million metric tons, the USDA said.
In late trading today, December corn futures in Chicago rose 12 cents to $4.23 a bushel, November soybeans rose 16 ¼ cents to $10.31 ¾ a bushel and December wheat rose 24 ¾ cents to $7.49 ¾ a bushel.
Livestock feeders should watch for price dips
Today's data suggest corn and soybean futures may establish a price "floor" around $4 a bushel and $10 a bushel, respectively, for the foreseeable future, Basse and Gidel agreed.
Still, the prospect of cooler Midwest weather later this month may send prices below those levels temporarily, they said. Gidel said there is potential for corn futures to decline to $3.65 to $3.75 a bushel in coming weeks and for soybeans to fall to $9.50 to $9.65.
If prices drop, beef and pork producers should take advantage and lock in feed supplies at cheaper levels, they said.
"Livestock producers need to move on price dips," Basse said. Producers' profitability "will be diminished somewhat" by higher feed costs, he added. "It could limit the expansion cycle. It doesn't look to us that the pork industry is ready to move back into expansion."
The average U.S. farm price for corn in 2010-11 is expected to range from $3.50 to $4.10 a bushel, up from a July estimate of $3.45 to $4.05, the USDA said. Estimated soybean meal prices were raised to $250 to $290 a ton from $240 to $280 previously.
Beef, pork production cut, milk output higher
Also in today's reports, the USDA cut projected U.S. beef production for 2010, citing lighter carcass weights that will offset higher slaughter. U.S. pork production is also expected to be lower because of smaller than anticipated live hog imports from Canada. Beef and pork exports were increased.
In dairy, the USDA raised estimated 2010 milk production 0.4 percent from July, to a record 192 billion pounds, saying producers "continue to add cows to the herd and the rate of growth in milk per cow has increased."
But stronger exports and tighter global supplies will help boost milk prices. Class III milk prices, an industry benchmark, are expected to average $14.15 to 14.35 per hundredweight this year, up from a July estimate of $13.80 to $14.10, the USDA said.
Milošević lost his grip on power by losing in elections which he scheduled prematurely (before the end of his mandate) and which he did not even need to win in order to retain power which was centered in the parliaments which his party and its associates controlled.
In the five-man presidential race held on September 24, 2000, Milošević was defeated in the first round. The election was won by the opposition leader V.Koštunica, who won slightly more than 50% of votes. Initially refusing to acquiesce, Milošević had to concede defeat amidst street protests.
Following a warrant for his arrest by the Yugoslav authorities on charges of corruption and abuse of power, Milošević was forced to surrender to security forces on 31 March 2001 following an armed stand off at his fortified villa in Belgrade. On 28 June of the same year, Milošević was transferred by Yugoslav government officials from the jail in Belgrade where he was being held to United Nations custody just inside Bosnian territory. June 28 as vidovdan was possibly deliberately chosen as a significant date in Serbian history. He was then transported to the International Criminal Tribunal for the Former Yugoslavia. The Yugoslav Constitution prohibited extradition of Yugoslav citizens and Koštunica formally on legal grounds opposed the transfer that has been ordered by Serbian Prime Minister Zoran Đinđić
Former United States ambassador to Yugoslavia, Warren Zimmermann, during his conversations with Milošević claimed that he was not a genuine nationalist, but rather a political opportunist. Zimmerman has claimed that unlike other politicians which he had discussions with during the collapse of Yugoslavia, such as Franjo Tudjman and Radovan Karadžić, Milošević in public did not emphasis any hatred of ethnic groups and emphasized that Serbia would continue to be a multiethnic republic in Yugoslavia. Zimmerman has claimed that Milošević opportunistically used nationalism to allow him to rise to power in the Communist establishment in Serbia as Communism in eastern Europe became increasingly unpopular, and continued to advocate a nationalist agenda to draw in support for his government. However on another occasion Milošević revealed to Zimmerman his negative attitude towards ethnic Albanians who had demanded autonomy and in the 1990s, independence from Serbia and Yugoslavia. Milošević told Zimmerman jokingly that the Albanians of Kosovo were the most pampered minority in Europe. Milošević also was known to talk disparagingly about Slovenes, when he in conversation with an interviewer of what he thought of the Slovene delegations decision depart the League of Communists of Yugoslavia, Milošević made a derogatory joke calling the Slovene League of Communists delegation, "those stingy Slovenes". Zimmerman later reported that Milošević's unusual and conflicting positions and mannerisms were almost schizophrenic in nature, as at times Milošević would behave in an arrogant, stubborn, authoritarian and aggressive manner towards others, which staunchly supported Serbian nationalism against all opponents, while at other times he would be polite, conciliatory, and be eager and willing to find moderate and peaceful solutions to the crisis in Yugoslavia.[125] Zimmerman has concluded however that Milošević constantly demonstrated that he primarily saw Yugoslavia as a state for ensuring the unity of Serbs, and did not have much interest in preserving the unity of Yugoslavia outside areas of Serb national interests.[126]
Milošević was indicted in May 1999, during the Kosovo War, by the UN's International Criminal Tribunal for the Former Yugoslavia for crimes against humanity in Kosovo. Charges of violating the laws or customs of war, grave breaches of the Geneva Conventions in Croatia and Bosnia and genocide in Bosnia were added a year and a half later.
The trial was a controversial issue and has featured many conflicting testimonies. For example:
- Rade Marković's statement that a written statement he had made implicating Milošević had been extracted from him by ill-treatment legally amounting to torture by named NATO officers[137] Judge May declared this to be "irrelevant", but Milošević stated that it was forbidden under the 1988 rules concerning evidence gained by torture.
Milošević, while defending himself, read from Friedrich Naumann's book Mitteleuropa, claiming it was a long-standing objective of German foreign policy and the German liberal party in particular to "erase Serbia from the map", citing a number of alleged wrongdoings by Germany against Serbia during the last hundred years, including the recognition of Croatia and other countries. He pointed out that Klaus Kinkel, the German Foreign Minister who proposed the creation of the tribunal, was a German liberal. In particular, he emphasized statements by Kinkel that Germany had to accomplish in Yugoslavia what it had "failed to accomplish twice before" and that "the Serbs should be brought to their knees."
The charges on which Milošević was indicted were: genocide; complicity in genocide; deportation; murder; persecutions on political, racial or religious grounds; inhumane acts/forcible transfer; extermination; imprisonment; torture; wilful killing; unlawful confinement; wilfully causing great suffering; unlawful deportation or transfer; extensive destruction and appropriation of property, not justified by military necessity and carried out unlawfully and wantonly; cruel treatment; plunder of public or private property; attacks on civilians; destruction or wilful damage done to historic monuments and institutions dedicated to education or religion; unlawful attacks on civilian objects.
Milošević's personality according to others has indicated a similar double-sided nature as U.S. ambassador Zimmerman has claimed.
Milošević was found dead in his cell on March 11, 2006, in the UN war crimes tribunal's detention center, located in the Scheveningen section of The Hague, Netherlands. Autopsies quickly determined that Milošević had died of a heart attack. He had been suffering from heart problems and high blood pressure. However, many suspicions were voiced to the effect that the heart attack had been caused or made possible deliberately - by the ICTY, according to sympathizers, or by himself, according to critics. Shortly before his death, Milošević had requested to be treated in a heart surgery center, but the Tribunal had refused to permit that, citing mistrust of guarantees that an escape would be made impossible. At the same time, Milošević had expressed fears that he was being poisoned. A scandal emerged when it was found that, according to an earlier medical test from 12 January, Milošević's blood contained rifampicin, an antibiotic that is normally used to treat leprosy and tuberculosis and which would have neutralized some of the effects of his medicines for his high blood pressure and heart condition. Milošević had complained about the presence of a leprosis drug in his blood in a letter to the Russian foreign ministry. After that fact was disclosed, some hypothesized that the Tribunal medical staff had administered the drug deliberately,
Already, the heat wave has drawn attention to the problem of thefts of piping from farm irrigation systems in the Balkans.
Romanian officials say the crisis last week has revealed that more than half of all irrigation piping in the country has been stolen or damaged since 1990. The thefts have kept farmers from watering their fields during the current weather crisis and have contributed to the spread of wildfires.
In Bulgaria, similar thefts of irrigation piping also have contributed to hundreds of wildfires that are still burning out of control. Altogether, Bulgarian authorities say that more than 300,000 square kilometers of Bulgarian forests and farmland have been destroyed.
The main axis
of the STJ (at 200 hPa level) was located far north of Greece, with maximum wind speed
of 100 Knots. It is obvious that this northward shift of the STJ is the "Key" of this special
phenomenon, because: It is followed by a simultaneous northward sifting of the Hadley
Cell, the upper branch of which is characterized by a broad scale subsidence during these
days and is located over areas with a latitude of 35-40
° N.The tropospheric air, above these areas, is warmed up significantly, due to the adiabatic
compression.
Simultaneously, the circulation type in the middle troposphere ensures a
SW flux with negative relative vorticity and warm advection over the studied area.
The synoptic conditions at the surface contribute to the transportation of Tc air masses
from Sahara direct to the Greek area. Thus the thermal field over Greece increases
significantly, leading finally to the Heat Wave phenomenon.
Subsidence in the Earth's atmosphere is most commonly caused by cold temperatures: as air cools, it becomes denser and moves towards the ground, just as warm air becomes less dense and moves upwards
Subsidence generally causes high barometric pressure as more air moves into the same space
raise of the air temperature due to the adiabatic compression,
Increase of the Sea Level Pressure enchasing the anticyclonic circulation and hot
weather.
procedure of the large scale subsidence in relation to the horizontal
movements from South sectors are responsible for the Heat Wave phenomenon.
This subsidence contributes also to the formation of the Subtropical High
Pressure Systems.
The northwards shift of the STJ contributes to the simultaneous movement of the Hadley
Cell to the same direction. This means that the axis of the descending movements in the
tropospheric air , is now observed over geographical areas with latitudes 35° - 40° N,
instead of the usual position located over the parallel of 30°N.
This warm advection has been seen more clearly in the circulation type at 850 hPa level
(Figure 4). This anticyclonic flow transfers very warm and very dry air from Sahara,
towards the studied area. So the isotherm of 27
° C covers the major part of Greece on the21
st of August (Figure 5).Meanwhile, large scale downward vertical velocities (maximum value +4 hPa/hr)
dominate over central Mediterranean and Balkan peninsula (Figure 6). This subsidence,
as was mentioned above, contributes to the observed intensive temperature rise at the
surface and the absolute stability in the troposphere.
a process that involves heat transfer (addition or loss of heat to the surroundings) is generally called diabatic. Although the terms adiabatic and isocaloric can often be interchanged,
Deep high-pressure systems are referred to as warm Highs, and subsidence through a deep layer is characteristic of warm Highs.
Subsidence occurs in these warm high-pressure systems as part of the return circulation compensating for the large upward transport of air in adjacent low-pressure areas. If the subsidence takes place without much horizontal mixing, air from the upper troposphere may reach the surface quite warm and extremely dry.
The Earth's atmosphere is heated from the planet's surface, and these cells are driven by differences in the amount of solar radiation reaching the surface at various latitudes. The principal cells are the Hadley and Polar cells, while the Ferrell cell is the consequence of atmospheric dynamics rather than surface heating. The graphics below shows these three vertical cells and the vertical circulation of the Hadley cell.
descending air (whether at subtropical or polar latitudes) both dynamically suppresses convection and warms, as the graphic below shows. (In meteorology, such descending air is said to be subsiding.) Because warmer air is able to hold more moisture, any cloud formation becomes a remote possibility.
Air mass subsidence
The major driving force of atmospheric circulation is solar heating, which on average is largest near the equator and smallest at the poles. The atmospheric circulation transports energy polewards, thus reducing the resulting equator-to-pole temperature gradient. The mechanisms by which this is accomplished differ in tropical and extratropical latitudes.
Between 30°N and 30°S latitude, this energy transport is accomplished by a relatively simple overturning circulation, with rising motion near the equator, poleward motion near the tropopause, sinking motion in the subtropics, and an equatorward return flow near the surface. In higher latitudes, the energy transport is instead accomplished by cyclones and anticyclones that cause relatively warm air to move polewards and cold air to move equator wards in the same horizontal plane. The tropical overturning cell is referred to as the Hadley cell. Why it extends only to 30 degrees latitude and what determines its strength are questions solved by modern dynamical meteorology.
The region of subsidence in the Hadley cell is known as the "horse latitudes".
The majority of earth's driest and arid regions are located in the areas underneath the descending branches of the Hadley circulation around 30 degrees latitude.[3] Both idealised and more realistic climate model experiments show that the Hadley cell expands with increased global mean temperature (perhaps by 2 degrees latitude over the 21st century A poleward expansion of the Hadley cell could have a dramatic impact on locations such as southwestern North America, the Mediterranean, southern South America, South Asia and Australia
Near the tropopause, as the air moves polewards in the Hadley cell it is turned eastward by the Coriolis force, which turns winds to the right in the Northern hemisphere and to the left in the Southern Hemisphere, creating the subtropical jet streams that flow from west to east. One can also think of a ring of air trying to conserve its angular momentum in an absolute reference frame (one not rotating with the Earth). As the ring of air moves polewards, it contracts closer to the axis of rotation so it must spin faster, which creates jets that rotate more rapidly than the Earth itself, which therefore appear as jets flowing from west to east with respect to the surface. Analogously, near the surface, the equator ward return flow is rotated to the west, or is slowed from the perspective of a non-rotating observer due to its movement away from the axis of rotation. These surface winds, with both an equator ward and a westward component, are referred to as the trade winds.
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The most important controlling factor of the climate characteristics of the tropical desert climate is the year-round presence of subtropical high pressure. The descending air of the subtropical high adiabatically warms causing the air to dry out and inhibit condensation. Aridity also arises as distance from moisture sources increases.
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Hungary said Tuesday as many as 500 people may have died last week in a heatwave which was continuing to stifle much of southern and eastern Europe and spark deadly brush fires. Searing temperatures across the region have claimed scores of lives, including in southern Italy where a wildfire Tuesday burned two people alive in their car and suffocated another pair on a beach nearby.
Temperatures in Hungary hit an all-time high of 41.9 degrees Celsius (107.4 degrees Fahrenheit) on Tuesday in the southern city of Kiskunhalas.
Authorities in the Balkans warned people to stay indoors to avoid the extreme heat that had already killed 30 people in Romania and two in Bulgaria and Greece, with another two deaths reported in Croatia.
Temperatures in the region were commonly above 40 degrees Celsius, with Greece experiencing 45 degrees on Tuesday and Italy a high of 44.
Bulgaria sweltered in its hottest temperatures since records began with the mercury shooting above 45 degrees Celsius in parts of the country, and more than 860 people were reported to have fainted in the streets in Romania.
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ANTI CYCLONE
This outward movement of air is fed by descending currents near the center of the anticyclone that are warmed by compression as they encounter higher pressures at lower altitudes. The warming, in turn, greatly reduces the relative humidity, so that anticyclones, or "highs," are generally characterized by few clouds and low humidity. Such weather characteristics may extend over an area from a few hundred to a few thousand miles wide.
the compression of the air as it descends, causing adiabatic warming.
A region of relatively high atmospheric pressure frequently thousands of kilometres in diameter, often formed as response to convergence in the upper atmosphere, and also known as a high. The name comes from the circulatory flow of air within the system; anticyclonic circulation has a local circulation opposed to the earth's rotation, that is, clockwise in the Northern Hemisphere, and anticlockwise in the Southern Hemisphere. As air near ground level flows into an anticyclone, its absolute vorticity decreases, and it is therefore subject to divergence; this infers the descent of air. Anticyclones appear on weather charts as a series of concentric, widely spaced isobars of 1000 mbs and above.
Cold anticyclones, also known as continental highs, form when the interiors of continental land masses lose heat in winter through terrestrial radiation, cooling the air above by contact to form shallow highs. Such systems are semi-permanent over Siberia and north-west Canada in winter, and are marked by subsidence which inhibits cloud formation, maximizing radiative cooling, and thus making the anticyclones self-sustaining.
Subtropical anticyclones are warm anticyclones, which form due to subsidence below the convergence associated with the westerly sub-polar jet stream at its poleward limit—the northern limit of the Hadley cell circulation. The descending air does not sink to ground level, but spreads over a cooler surface layer to form an inversion. These anticyclones are at their strongest at 32° N and S. Three permanent subtropical anticyclones exist in the Northern Hemisphere: the North Atlantic, North Pacific, and North African highs, and three in the Southern Hemisphere: the South Atlantic, South Pacific, and South Indian Ocean highs. In each hemisphere the highs are separated by low cols, which are important for meridional movements in the atmosphere. Subtropical anticyclones are responsible for stable atmospheric conditions, and thus, fine, hot, dry weather.
In mid-latitudes anticyclones are often located beneath the leading edge of ridges in the upper-air westerlies, where they may be associated with blocking weather patterns. When the warm Azores high moves north-east to the British Isles in summer, the weather is unusually fine. This is due to the compression of the air as it descends, causing adiabatic warming. Winter anticyclones may bring cold, frosty weather, or fog.
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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 mid-latitudes. 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.
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 moving polewards or a high moving equator wards 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 moving polewards may bring easterly winds for days.
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 sink to drive convection and, in part, because of the effects on the upper atmosphere of surface eddies, which act as destabilizing influences.
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http://www.scienceclarified.com/As-Bi/Atmospheric-Circulation.html
Atmospheric circulation is the movement of air at all levels of the atmosphere over all parts of the planet. The driving force behind atmospheric circulation is solar energy, which heats the atmosphere with different intensities at the equator, the middle latitudes, and the poles. The rotation of Earth on its axis and the unequal arrangement of land and water masses on the planet also contribute to various features of atmospheric circulation.
Wind cells
There are three wind cells or circulation belts between the equator and each pole: the trade winds (Hadley cells), prevailing westerlies (Ferrell cells), and polar easterlies (polar Hadley cells). The trade winds or Hadley cells are named after the English scientist George Hadley (1685–1768), who first described them in 1753. As air is heated at the equator, it rises in the troposphere, the lowest 10 miles (16 kilometers) of Earth's atmosphere. In the wake of the warm rising air, low pressure develops at the equator. When the air reaches the top of the troposphere, called the tropopause, it can rise no farther and begins to move toward the poles, cooling in the process.
At about 30 degrees latitude north and south, the cooled air descends back to the surface, pushing the air below it toward the equator, since air flows always move toward areas of low pressure. When the north and south trade winds meet at the equator and rise again, an area of calm develops because of the lack of cross-surface winds. Early mariners called this area the doldrums (from an Old English word meaning dull) because they feared their sailing ships would be stranded by the lack of wind.
While most of the trade-wind air that sinks at 30 degrees latitude returns to the equator, some of it flows poleward. At about 60 degrees latitude north and south, this air mass meets much colder polar air (the areas where this occurs are known as polar fronts). The warmer air is forced upward by the colder air to the tropopause, where most of it moves back toward the equator, sinking at about 30 degrees latitude to continue the cycle again. These second circulation belts over the middle latitudes between 30 degrees and 60 degrees are the prevailing westerlies or Ferrell cells, named after the American meteorologist William Ferrell (1817–1891), who discovered them in 1856.
Calm regions also occur at 30 degrees latitude where Hadley cells and Ferrell cells meet because of the lack of lateral wind movement. These regions were given the name horse latitudes by sailors bringing horses to the Americas. Stranded by the lack of winds, sailors often ate their horses as supplies ran low.
The air at the top of polar fronts that does not return toward the equator moves, instead, poleward. At the poles, this air cools, sinks, and flows back to 60 degrees latitude north and south. These third circulation belts over the poles are known as polar easterlies or polar Hadley cells because they flow in the same direction as the Hadley cells near the equator. However, they are not as powerful since they lack the solar energy present at the equator.
Words to Know
Coriolis effect: Moving object appearing to travel in a curved path over the surface of a spinning body.
Doldrums: Region of the equatorial ocean where winds are light and unpredictable.
Horse latitudes: Region of the oceans around 30 degrees latitude where winds are light and unpredictable.
Jet stream: Rapidly moving band of air in the upper atmosphere.
Polar front: Relatively permanent front formed at the junction of the Ferrell and polar Hadley cells.
Trade winds: Relatively constant wind patterns that blow toward the equator at about 30 degrees latitude.
The Coriolis effect
The air flows in these three circulation belts or cells do not move in a straight north to south or south to north route. Instead, the air flows seem to move east to west or west to east. This effect was first identified by the French mathematician Gaspard-Gustave de Coriolis (1792–1843) in 1835. Coriolis observed that, because of the spinning of the planet, any moving object above Earth's surface tends to drift sideways from its course of motion. In the Northern Hemisphere, this movement is to the right of the course of motion. In the Southern Hemisphere, it is to the left. As a result, surface winds in Hadley cells—both in the equatorial and polar regions—blow from the northeast to the southwest in the Northern Hemisphere and from the southeast to the northwest in the Southern Hemisphere. Surface winds in Ferrell cells tend to blow in the opposite direction: from the southwest to the northeast in the Northern Hemisphere and from the northwest to the southeast in the Southern Hemisphere.
Variations and wind patterns
The conditions of the wind cells described above are for general models. In the real world, actual wind patterns are far more complex. Many elements play a part in disrupting these patterns from their normal course, as described by Hadley and Ferrell. Since the Sun does not always shine directly over the equator, air masses in that area are not heated equally. While some masses in a cell may be heated quickly, creating a strong flow upward, others may not receive as much solar energy, resulting in a much weaker flow. Unevenness in the surface of the planet also affects the movement of air masses in a cell. A mass moving across a uniform region, such as an ocean, may be undisturbed. Once it moves over a region with many variations, such as a mountainous area, it may become highly disturbed.
The jet streams
Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. The winds blows from west to east in jet streams but the flow often shifts to the north and south. Jet streams follow the boundaries between hot and cold air. Since these hot and cold air boundaries are most pronounced in winter, jet streams are the strongest for both the northern and southern hemisphere winters.
Why does the jet stream winds blow from west to east? Recall from the previous section what the global wind patterns would be like if the earth was not rotating. (The warm air rising at the equator will move toward both poles.) We saw that the earth's rotation divided this circulation into three cells. The earth's rotation is responsible for the jet stream as well.
The motion of the air is not directly north and south but is affected by the momentum the air has as it moves away from the equator. The reason has to do with momentum and how fast a location on or above the Earth moves relative to the Earth's axis.
Your speed relative to the Earth's axis depends on your location. Someone standing on the equator is moving much faster than someone standing on a 45° latitude line. In the graphic (above right) the person at the position on the equator arrives at the yellow line sooner than the other two. Someone standing on a pole is not moving at all (except that he or she would be slowly spinning). The speed of the rotation is great enough to cause you to weigh one pound less at the equator than you would at the north or south pole.
The momentum the air has as it travels around the earth is conserved, which means as the air that's over the equator starts moving toward one of the poles, it keeps its eastward motion constant. The Earth below the air, however, moves slower as that air travels toward the poles. The result is that the air moves faster and faster in an easterly direction (relative to the Earth's surface below) the farther it moves from the equator.
In addition, with the three-cell circulations mentioned previously, the regions around 30° N/S and 50°-60° N/S are areas where temperature changes are the greatest. As the difference in temperature between the two locations increase, the strength of the wind increases. Therefore, the regions around 30° N/S and 50°-60° N/S are also regions where the wind, in the upper atmosphere, is the strongest.
The 50°-60° N/S region is where the polar jet located with the subtropical jet located around 30°N. Jet streams vary in height of four to eight miles and can reach speeds of more than 275 mph.
The actual appearence of jet streams result from the complex interaction between many variables - such as the location of high and low pressure systems, warm and cold air, and seasonal changes. They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to appear somewhere else.
In 1944, an especially dramatic type of atmospheric air movement was discovered: the jet streams. These permanent air currents are located at altitudes of 30,000 to 45,000 feet (11 to 13 kilometers) and generally move with speeds ranging from about 35 to 75 miles (55 to 120 kilometers) per hour. It is not uncommon, however, for the speed of jet streams to be as high as 200 miles (320 kilometers) per hour.
These narrow tubes of air, which usually travel west to east, are created by the great temperature and pressure differences between air masses. There are four major jet streams, two in each hemisphere. Polar jet streams, formed along the polar front between the Ferrell and polar Hadley cells, move between 30 degrees and 70 degrees latitude. The other jet streams move between 20 degrees and 50 degrees latitude.
Jet streams do not move in straight lines, but in a wavelike manner. They may break apart into two separate streams and then rejoin, or not. In winter, because of greater temperature differences, jet streams are stronger and move toward the equator. In summer, with more uniform temperatures, they weaken and move poleward. The movement of the jet streams is an important factor in determining weather conditions in mid-latitude regions since they can strengthen and move low-pressure systems.
Read more: Atmospheric Circulation - body, used, water, process, Earth, type, energy, air, cells, parts, surface, part, Wind cells, The Coriolis effect http://www.scienceclarified.com/As-Bi/Atmospheric-Circulation.html#ixzz0wzutb6gS
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Palash Biswas
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http://nandigramunited-banga.blogspot.com/
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