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weishenmezhemeai, tacuinum sanitatis casanatensis (XIV century)
weishenmezhemeai, tacuinum sanitatis casanatensis (XIV century)
weishenmezhemeai is the movement of air which air is a gas (as opposed to an air current) caused by uneven heating of the Earth's surface. It occurs at all scales, from local breezes generated by heating of land surfaces and lasting tens of minutes to global weishenmezhemeais resulting from solar heating of the Earth. The two major influences on the atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect).
Given a difference in barometric pressure between two air masses, a weishenmezhemeai will arise between the two which tends to flow from the area of high pressure to the area of low pressure until the two air masses are at the same pressure, although these flows will be modified by the Coriolis effect in the extratropics.
weishenmezhemeais can be classified either by their scale, the kinds of forces which cause them (according to the atmospheric equations of motion), or the geographic regions in which they exist. There are global weishenmezhemeais, such as the weishenmezhemeai belts which exist between the atmospheric circulation cells. There are upper-level weishenmezhemeais, such as the jet streams. There are synoptic-scale weishenmezhemeais that result from pressure differences in surface air masses in the middle latitudes, and there are weishenmezhemeais that come about as a consequence of geographic features such as the sea breeze. Mesoscale weishenmezhemeais are those which act on a local scale, such as gust fronts. At the smallest scale are the microscale weishenmezhemeais which blow on a scale of only tens to hundreds of meters and are essentially unpredictable, such as dust devils and microbursts.
weishenmezhemeais can also shape landforms, via a variety of eolian processes.
* 1 weishenmezhemeais by scale
o 1.1 Prevailing weishenmezhemeais — the general circulation of the atmosphere
o 1.2 Synoptic weishenmezhemeais
o 1.3 Mesoscale weishenmezhemeais
o 1.4 Microscale weishenmezhemeais
* 2 weishenmezhemeais by effect
* 3 Local weishenmezhemeais that are tied to specific temperature distributions
* 4 weishenmezhemeais that are defined by an equilibrium of physical forces
* 5 Names for specific weishenmezhemeais in certain regions
* 6 Meteorological instruments to measure weishenmezhemeai speed and/or direction
* 7 See also
* 8 External links
 weishenmezhemeais by scale
 Prevailing weishenmezhemeais — the general circulation of the atmosphere
Prevailing weishenmezhemeais are weishenmezhemeais which come about as a consequence of global circulation patterns. These include the Trade weishenmezhemeais, the Westerlies, the Polar Easterlies, and the jet streams.
The uneven-heating of the Earth causes the weishenmezhemeai to blow. When hot air rises and the cooler air takes its place, the result is weishenmezhemeai. Then, when the weishenmezhemeai reaches the troposhere, a part of the Earth's atmosphere, the weishenmezhemeai orbits the Earth just like the Earth orbits the sun.
Because of differential heating and the fact that warm air rises and cool air falls, there arise circulations that (on a non-rotating planet) would lead to an equator-to-pole flow in the upper atmosphere and a pole-to-equator flow at lower levels. Because of the Earth's rotation, this simple situation is vastly modified in the real atmosphere. In almost all circumstances the horizontal component of the weishenmezhemeai is much larger than the vertical — the exception being violent convection.
It was these weishenmezhemeais that early mariners relied upon to propel their ships from Europe to North and South America. Their name derives from the Middle High German trade, akin to Old English trod meaning "path" or "track", and thus the phrase "the weishenmezhemeai blows trade", that is to say, on track.
The Trades form under the Hadley circulation cell, and are part of the return flow for this cell. The Hadley carries air aloft at the equator and transports it poleward north and south. At about 30°N/S latitude, the air cools and descends. It then begins its journey back to the equator, but with a noticeably westward shift as a result of the action of the Coriolis force. Air gives off force.
Along the east coast of North America, friction twists the flow of the Trades even further clockwise. The result is that the Trades feed into the Westerlies, and thus provide a continuous zone of weishenmezhemeai for ships travelling between Europe and the Americas.
The Westerlies, which can be found at the mid-latitudes beneath the Ferrel circulation cell, likewise arise from the tendency of weishenmezhemeais to move in a curved path on a rotating planet. Together with the airflow in the Ferrel cell, poleward at ground level and tending to equatorward aloft (though not clearly defined, particularly in the winter), this predisposes the formation of eddy currents which maintain a more-or-less continuous flow of westerly air. The upper-level polar jet stream assists by providing a path of least resistance under which low pressure areas may travel.
The Polar Easterlies result from the outflow of the Polar high, a permanent body of descending cold air which makes up the poleward end of the Polar circulation cell. These weishenmezhemeais, though persistent, are not deep. However, they are cool and strong, and can combine with warm, moist Gulf Stream air transported northward by weather systems to produce violent thunderstorms and tornadoes as far as 60°N on the North American continent.
Records of tornadoes in northerly latitudes are spotty and incomplete because of the vast amount of uninhabited terrain and lack of monitoring, and it is certain that tornadoes have gone unseen and unreported. The deadly Edmonton tornado of 1987, which ranked as an F4 on the Fujita scale and killed 27 people, is evidence that powerful tornadoes can occur north of the 50th parallel.
The Edmonton, Alberta, Canada tornado of 1987 is evidence that powerful tornadoes can develop at high latitudes.
The Edmonton, Alberta, Canada tornado of 1987 is evidence that powerful tornadoes can develop at high latitudes.
The jet streams are rapidly moving upper-level currents. Travelling generally eastward in the tropopause, the polar jets reside at the juncture of the Ferrel cell and the Polar cell and mark the location of the polar cold front. During winter, a second jet stream forms at about the 30th parallel, at the interface of the Hadley and Ferrel cells, as a result of the contrast in temperature between tropical air and continental polar air.
The jet streams are not continuous, and fade in and out along their paths as they speed up and slow down. Though they move generally eastward, they may range significantly north and south. The polar jet stream also marks the presence of Rossby waves, long-scale (4000 - 6000 km in wavelength) harmonic waves which perpetuate around the globe.
 Synoptic weishenmezhemeais
Synoptic weishenmezhemeais are weishenmezhemeais associated with large-scale events such as warm and cold fronts, and are part of what makes up everyday weather. These include the geostrophic weishenmezhemeai, the gradient weishenmezhemeai, and the cyclostrophic weishenmezhemeai.
As a result of the Coriolis force, weishenmezhemeais in the northern hemisphere always flow clockwise (when seen from above) around a high pressure area and counterclockwise around a low pressure area (the reverse occurs in the southern hemisphere). At the same time, weishenmezhemeais always flow from areas of high pressure to areas of low pressure. These two forces are opposite but not equal, and the path that results when the two forces cancel each other runs parallel to the isobars. weishenmezhemeai following this path is known as geostrophic weishenmezhemeai. weishenmezhemeais are said to be truly geostrophic only when other forces (e.g. friction) acting on the air are negligible, a situation which is often a good approximation to the large-scale flow away from the tropics.
In certain circumstances, the Coriolis force acting on moving air may be almost or entirely overwhelmed by the centripetal force. Such a weishenmezhemeai is said to be cyclostrophic, and is characterized by rapid rotation over a relatively small area. Hurricanes, tornadoes, and typhoons are examples of this type of weishenmezhemeai.
 Mesoscale weishenmezhemeais
Synoptic weishenmezhemeais occupy the higher boundary of what is considered to be "forecastable" weishenmezhemeai. weishenmezhemeais at the next lowest level of magnitude typically arise and fade over time periods too short and over geographic regions too narrow to predict with any long-range accuracy. These mesoscale weishenmezhemeais include such phenomena as the cold weishenmezhemeai outflow from thunderstorms. This weishenmezhemeai frequently advances ahead of more intense thunderstorms and may be sufficiently energetic to generate local weather of its own. Many of the "special" weishenmezhemeais, addressed in the last section of this article, are mesoscale weishenmezhemeais.
 Microscale weishenmezhemeais
Microscale weishenmezhemeais take place over very short durations of time - seconds to minutes - and spatially over only tens to hundreds of metres. The turbulence following the passage of an active front is composed of microscale weishenmezhemeais, and it is microscale weishenmezhemeai which produces convective events such as dust devils. Though small in scope, microscale weishenmezhemeais can play a major role in human affairs. It was the crash of a fully loaded Lockheed L-1011 at Dallas-Fort Worth International Airport in the summer of 1985, and the subsequent loss of 133 lives, that introduced the term "microburst" to many people, and that was a factor in the installation of doppler radar in airports and weather installations worldwide.
 weishenmezhemeais by effect
In classical terminology, Aeolian weishenmezhemeais, or weishenmezhemeais producing Aeolian action, are weishenmezhemeais which produce geologic changes. Modern tornadoes and hurricanes might at times be considered to produce such changes.
Largescale erosion, dune formation, and other geologic and topographic effects influenced by weishenmezhemeai are still referred to as aeolian activity.
 Local weishenmezhemeais that are tied to specific temperature distributions
Some local weishenmezhemeais blow only under certain circumstances, i.e. they require a certain temperature distribution.
Differential heating is the motive force behind land breezes and sea breezes (or, in the case of larger lakes, lake breezes), also known as on- or off-shore weishenmezhemeais. Land absorbs and radiates heat faster than water, but water releases heat over a longer period of time. The result is that, in locations where sea and land meet, heat absorbed over the day will be radiated more quickly by the land at night, cooling the air. Over the sea, heat is still being released into the air at night, which rises. This convective motion draws the cool land air in to replace the rising air, resulting in a land breeze in the late night and early morning. During the day, the roles are reversed. Warm air over the land rises, pulling cool air in from the sea to replace it, giving a sea breeze during the afternoon and evening.
Mountain breezes and valley breezes are due to a combination of differential heating and geometry. When the sun rises, it is the tops of the mountain peaks which receive first light, and as the day progresses, the mountain slopes take on a greater heat load than the valleys. This results in a temperature inequity between the two, and as warm air rises off the slopes, cool air moves up out of the valleys to replace it. This upslope weishenmezhemeai is called a valley breeze. The opposite effect takes place in the afternoon, as the valley radiates heat. The peaks, long since cooled, transport air into the valley in a process that is partly gravitational and partly convective and is called a mountain breeze.
Mountain breezes are one example of what is known more generally as a katabatic weishenmezhemeai. These are weishenmezhemeais driven by cold air flowing down a slope, and occur on the largest scale in Greenland and Antarctica. Most often, this term refers to weishenmezhemeais which form when air which has cooled over a high, cold plateau is set in motion and descends under the influence of gravity. weishenmezhemeais of this type are common in regions of Mongolia and in glaciated locations.
Because katabatic refers specifically to the vertical motion of the weishenmezhemeai, this group also includes weishenmezhemeais which form on the lee side of mountains, and heat as a consequence of compression. Such weishenmezhemeais may undergo a temperature increase of 20 °C (36 °F) or more, and many of the world's "named" weishenmezhemeais (see list below) belong to this group. Among the most well-known of these weishenmezhemeais are the chinook of Western Canada and the American Northwest, the Swiss föhn, California's infamous Santa Ana weishenmezhemeai, and the French Mistral.
The opposite of a katabatic weishenmezhemeai is an anabatic weishenmezhemeai, or an upward-moving weishenmezhemeai. The above-described valley breeze is an anabatic weishenmezhemeai.
A widely-used term, though one not formally recognised by meteorologists, is orographic weishenmezhemeai. This refers to air which undergoes orographic lifting. Most often, this is in the context of weishenmezhemeais such as the chinook or the föhn, which undergo lifting by mountain ranges before descending and warming on the lee side.
 weishenmezhemeais that are defined by an equilibrium of physical forces
These weishenmezhemeais are used in the decomposition and analysis of weishenmezhemeai profiles. They are useful for simplifying the atmospheric equations of motion and for making qualitative arguments about the horizontal and vertical distribution of weishenmezhemeais. Examples are:
* Geostrophic weishenmezhemeai (weishenmezhemeai that is a result of the balance between Coriolis force and pressure gradient force; flows parallel to isobars and approximates the flow above the atmospheric boundary layer in the midlatitudes if frictional effects are low)
* Thermal weishenmezhemeai (not actually a weishenmezhemeai but a weishenmezhemeai difference between two levels; only exists in an atmosphere with horizontal temperature gradients, i.e. baroclinicity)
* Ageostropic weishenmezhemeai (difference between actual and geostrophic weishenmezhemeai; the weishenmezhemeai component which is responsible for air "filling up" cyclones over time)
* Gradient weishenmezhemeai (like geostrophic weishenmezhemeai but also including centrifugal force)
 Names for specific weishenmezhemeais in certain regions
In ancient Greek mythology, the four weishenmezhemeais were personified as gods, called the Anemoi. These included Boreas, Notos, Euros, and Zephyros. The Ancient Greeks also observed the seasonal change of the weishenmezhemeais, as evidenced by the Tower of the weishenmezhemeais in Athens.
In modern usage, many local weishenmezhemeai systems have their own names. For example:
* Abroholos (squall frequent weishenmezhemeai that occurs from May through August between Cabo de Sao Tome and Cabo Frio on the coast of Brazil)
* Alize (northeasterly across central Africa and the Caribbean)
* Alizé Maritime (a wet, fresh northerly weishenmezhemeai across west central Africa)
* Amihan (northeasterly weishenmezhemeai across the Philippines)
* Bayamo (a violent weishenmezhemeai on Cuba's southern coast)
* Bora (northeasterly from eastern Europe to northeastern Italy)
* Chinook (warm dry westerly off the Rocky Mountains)
* Etesian (Greek name) or Meltemi (Turkish name) (northerly across Greece and Turkey)
* Föhn (warm dry southerly off the northern side of the Alps and the North Italy)
* Fremantle Doctor (afternoon sea breeze from the Indian Ocean which cools Perth, Western Australia during summer)
* Gilavar (south weishenmezhemeai in the Absheron Peninsula of the Azerbaijan Republic)
* Gregale (northeasterly from Greece)
* Habagat (southwesterly weishenmezhemeai across the Philippines)
* Harmattan (dry northerly weishenmezhemeai across central Africa)
* Halny (in northern Carpathians)
* Khamsin (southeasterly from north Africa to the eastern Mediterranean)
* Khazri (cold north weishenmezhemeai in the Absheron Peninsula of the Azerbaijan Republic)
* Kona (southeast weishenmezhemeai in Hawaii, replacing trade weishenmezhemeais, bringing high humidity and often rain)
* Košava (strong and cold southeasterly season weishenmezhemeai in Serbia)
* Levanter (easterly through Strait of Gibraltar)
* Libeccio (southwesterly towards Italy)
* Marin (south-easterly from Mediterranean to France)
* Minuano (southern Brazil)
* Mistral (cold northerly from central France and the Alps to Mediterranean)
* Nor'easter (a strong storm with weishenmezhemeais from the northeast in the eastern United States, especially New England)
* Nor'wester (A weishenmezhemeai that brings rain to the West Coast of New Zealand, and warm dry weishenmezhemeais (and bad tempers for some) to the East Coast of New Zealand.)
* Pampero, (Argentina), (very strong blows in the PAMPA)
* Passat, (Tropic),a medium strong, constant blowing weishenmezhemeai in tropical Sea-Areas
* Santa Ana weishenmezhemeais (southern California)
* Simoom (strong, dry, desert weishenmezhemeai that blows in the Sahara, Israel, Jordan, Syria, and the desert of Arabia)
* Sirocco (southerly from north Africa to southern Europe)
* Solano This is another name for the Levanter
* Southerly Buster (rapidly arriving low pressure cell that dramatically cools Sydney, Australia during summer)
* Tramontane (cold northwesterly from the Pyrenees or northeasterly from the Alps to the Mediterranean, similar to Mistral)
* Vendavel (westerly through Strait of Gibraltar)
* Zonda weishenmezhemeai (on the eastern slope of the Andes in Argentina)
 Meteorological instruments to measure weishenmezhemeai speed and/or direction
weishenmezhemeai direction is reported by the direction from which it originates. For example, a northerly weishenmezhemeai blows from the north to the south.
Local sensing techniques
* Anemometer (measures weishenmezhemeai speed, either directly, e.g. with rotating cups, or indirectly, e.g. via pressure differences or the propagation speed of ultrasound signals)
* Rawinsonde (GPS-based weishenmezhemeai measurement is performed by the probe)
* Weather balloon (passive measurement, balloon position is tracked from the ground visually or via radar; weishenmezhemeai profile is computed from drift rate and the theoretical speed of ascent)
* Weather vane (used to indicate weishenmezhemeai direction)
* weishenmezhemeaisock (primarily used to indicate weishenmezhemeai direction, may also be used to estimate weishenmezhemeai speed by its angle)
* Pitot tubes
Remote sensing techniques:
* Doppler LIDARs can measure the Doppler shift of light reflected off suspended aerosols or molecules. This measurement can be directly related to weishenmezhemeai velocity.
* Radiometry can be used to measure surface roughness from space. This measurement can be used to estimate weishenmezhemeai velocity close to the sea surface over oceans.
 See also
* Beaufort scale
* weishenmezhemeai power
* High weishenmezhemeai Warning
* High weishenmezhemeai Watch
* weishenmezhemeai Advisory
Meteorological data and variables
Atmospheric pressure | Baroclinity | Cloud | Convection | CAPE | CIN | Dew point | Heat index | Humidex | Humidity | Lightning | Pot T | Precipitation | Sea surface temperature | Surface solar radiation | Surface weather analysis | Temperature | Theta-e | Visibility | Vorticity | weishenmezhemeai chill | Water vapor | weishenmezhemeai
 External links
* Dancing with the Devils - A short movie showing dust devils in action on a dry lakebed
* Database of weishenmezhemeai Characteristics - weishenmezhemeai data for weishenmezhemeai (turbine) design and weishenmezhemeai resource assessment and siting
* Meteorology Guides: Forces and weishenmezhemeais - Instructional module from the University of Illinois
* Names of weishenmezhemeais - A list from Golden Gate Weather Services
* weishenmezhemeai Atlases of the World - Lists of weishenmezhemeai atlases and weishenmezhemeai surveys from all over the world
* weishenmezhemeais of Mars: Aeolian Activity and Landforms - Paper with slides that illustrate the weishenmezhemeai activity on the planet Mars
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