A polar low is a small-scale, short-lived atmospheric low pressure system A low pressure area, or "low", is a region where the atmospheric pressure at sea level is lower in relation to surrounding locations. Low pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The name for the process concerning the formation of low pressure areas is known as cyclogenesis (depression) that is found over the ocean areas poleward of the main polar front In meteorology, the polar front is the boundary between the polar cell and the Ferrel cell in each hemisphere. At this boundary a sharp gradient in temperature occurs between these two air masses, each at very different temperatures in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than 1,000 kilometres (620 mi) and exist for no more than a couple of days. They are part of the larger class of mesoscale Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers. Examples of mesoscale weather systems are sea breezes, squall lines, and mesoscale convective complexes weather systems. Polar lows can be difficult to detect using conventional weather reports and are a hazard to high-latitude operations, such as shipping and gas and oil platforms. Polar lows have been referred to by many other terms, such as polar mesoscale vortex, Arctic hurricane, Arctic low, and cold air depression. Today the term is usually reserved for the more vigorous systems that have near-surface winds of at least 17 m/s (38 mph).[1]

Contents

History

Polar lows were first identified on the meteorological satellite imagery that became available in the 1960s, which revealed many small-scale cloud vortices at high latitudes. The most active polar lows are found over certain ice-free maritime areas in or near the Arctic The Arctic is the region around the Earth's North Pole, opposite the Antarctic region around the South Pole. The Arctic includes the Arctic Ocean (which overlies the North Pole) and parts of Canada, Greenland (a territory of Denmark), Russia, the United States (Alaska), Iceland, Norway, Sweden and Finland during the winter, such as the Norwegian Sea The Norwegian Sea is part of the North Atlantic Ocean, northwest of Norway, located between the North Sea (i.e. north of Scotland) and the Greenland Sea, Barents Sea Barents Sea is a part of the Arctic Ocean located north of Norway and Russia. Known in the Middle Ages as the Murman Sea, the sea takes its current name from the Dutch navigator Willem Barents. It is a rather deep shelf sea (average depth 760 feet (230 m) and maximum depth 1,480 feet (450 m) ), bordered by the shelf edge towards the Norwegian Sea, Sea of Japan The Sea of Japan is a marginal sea of the western Pacific Ocean, bordered by Japan, South Korea, North Korea and Russia. It is referred to in North Korea as the Korea East Sea and in South Korea as the East Sea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure. There is currently a dispute at the United, and Gulf of Alaska The Gulf of Alaska is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found. Polar lows dissipate rapidly when they make landfall. Antarctic The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence. The region covers some 20% of the Southern Hemisphere, of which 5.5% (1 systems tend to be weaker than their northern counterparts since the air-sea temperature differences around the continent are generally smaller. However, vigorous polar lows can be found over the Southern Ocean The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions. This ocean zone is where cold,.

Structure

Polar lows can have a wide range of cloud signatures in satellite imagery, but two broad categories of cloud forms have been identified. The first is the "spiraliform" signature consisting of a number of cloud bands wrapped around the centre of the low. Some polar lows have the appearance in satellite imagery of tropical cyclones, with deep thunderstorm clouds surrounding a cloud-free ‘eye The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather of a cyclone occurs. The cyclone's lowest barometric pressure occurs in the’, which has given rise to the use of the term "Arctic hurricane" to describe some of the more active lows. These systems are more common deep within the polar air. The second is a "comma-shaped" signature that is found more frequently with systems closer to the polar front.

Formation

See also: Cyclogenesis

Polar lows form for a number of different reasons, and a spectrum of systems is observed on satellite imagery. A number of lows develop on horizontal temperature gradients through baroclinic instability In fluid dynamics, the baroclinity is a measure of the stratification in a fluid. In meteorology a baroclinic atmosphere is one for which the density depends on both the temperature and the pressure; contrast this with barotropic atmosphere, for which the density depends only on the pressure. In atmospheric terms, the barotropic zones of the Earth, and these can have the appearance of small frontal depressions. At the other extreme are the polar lows with extensive cumulonimbus Cumulonimbus is a type of cloud that is tall, dense, and involved in thunderstorms and other intense weather. Cumulonimbus means "column rain" in Latin. It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold front in a squall line. They create lightning through the heart of the cloud clouds, which are often associated with cold pools in the mid- to upper-troposphere The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and 99% of its water vapor and aerosols.

Forecasting

See also: Weather forecasting Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century. Weather forecasts are made by collecting quantitative data about the current

Polar lows are very difficult to forecast and a nowcasting Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century. Weather forecasts are made by collecting quantitative data about the current approach is often used, with the systems being advected with the mid-tropospheric flow. Numerical weather prediction models are only just getting the horizontal and vertical resolution to represent these systems.

See also

References

  1. ^ Rasmussen,E.A. and Turner, J.(2003). Polar Lows: Mesoscale Weather Systems in the Polar Regions, Cambridge University Press, Cambridge, pp 612. ISBN 0521624304.

External links

Cyclones In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale cyclonic circulations are centered on areas of and Anticyclones An anticyclone is a weather phenomenon defined by the National Weather Service's glossary as "A large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere". Effects of surface-based anticyclones include clearing skies as well as of the world
Types Extratropical Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and horizontal gradients in temperature and dew point – Meso-scale A mesocyclone is a vortex of air, approximately 2 to 10 km in diameter , within a convective storm. That is, it is air that rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a severe – Polar Polar cyclones are low-pressure areas which strengthen in the winter and weaken in the summer. A polar cyclone is a low pressure weather system usually spanning 1,000–2,000 kilometers in which the air is circulating in a counter-clockwise fashion (in the northern hemisphere). The reason for the rotation is the same as any other cyclone, the – Subtropical cyclone A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National Hurricane Center in 1972. Subtropical cyclones began to/Subtropical ridge The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during daylight hours caused by the stable atmosphere found – Tropical A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic
Annual anticyclones Siberian High 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. It reaches its greatest size and strength in the winter, when the air temperature near the center of the high-pressure cell or anticyclone is often lower than -40 °C (-40 °F). The sea-level pressure (atmospheric – Azores High The Azores High, , is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low. The system influences the weather and climatic patterns of vast areas of North Africa and Europe (Bermuda/North Atlantic) – North American High The North American High is an impermanent high-pressure area or anticyclone created by anticyclogenesis (anticyclone + the Greek word genesis, meaning "birth, origin"), a formative process that occurs when cool or cold dry air settles onto North America (Canadian/Greenland) – South Atlantic High South Atlantic High is a semipermanent pressure high centered at about 25°S, 15°W, in the Atlantic Ocean. It is also called the St. Helena High. It can stretch thousands of miles across the South Atlantic affecting shipping. Sailors try to find a "corridor" through using the low pressure systems forming off the coast of Brazil that (St.Helena) – Pacific High The Pacific high is a subtropical anticyclone located in the south east of the Pacific Ocean making the west coast of South America arid. Sechura and Atacama deserts as the whole climate of Chile are heavily influenced by this semipermanent high pressure area – Scandinavian High – Mascarene High (Indian) – Australian High – Antarctic High
Annual cyclones Aleutian low The Aleutian Low is a semipermanent low pressure center located near the Aleutian Islands during the winter. It is one of the main centers of action in the atmospheric circulation of the Northern Hemisphere (Alaska/Far East Russia) - Icelandic Low The Icelandic Low is a semi-permanent centre of low atmospheric pressure found between Iceland and southern Greenland and extending in the Northern Hemisphere winter into the Barents Sea. In summer it weakens and splits into two centres, one near Davis Strait and the other west of Iceland. It is a principal centre of action in the atmosphere - Kona low Kona storms are a type of seasonal cyclone in the Hawaiian Islands, usually formed in the winter from winds coming from the Westerly "kona" (normally leeward) direction. They are mainly cold core cyclones, which places them in the extratropical cyclone rather than the subtropical cyclone category. Hawaii typically experiences two to(Hawaii) – Polar low

Categories: Types of cyclone There are a number of types of cyclone in meteorology. The most recognisable of these from name alone is arguably the tropical variety, though tropical cylones are just one type of cyclonic weather system of many. Cyclones in meteorology can vary in scale from small mesocyclones through to large extratropical cyclones, to often smaller but far | Barents Sea Categories: Seas of Russia | Seas of Norway | Marginal seas of the Arctic Ocean

 

The above information uses material from Wikipedia and is licensed under the GNU Free Documentation License The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a.
Some facts may not have been fully verified for accuracy. [Disclaimers Wikipedia is an online open-content collaborative encyclopedia, that is, a voluntary association of individuals and groups working to develop a common resource of human knowledge. The structure of the project allows anyone with an Internet connection to alter its content. Please be advised that nothing found here has necessarily been reviewed by]
This page was last archived by our server on Wed Feb 24 05:55:55 2010. [ refresh local cache ]
Displaying this page or its contents does not use any Wikimedia Foundation's resources.
The owners of this site proudly support the Wikimedia Foundation.

[Hide]▼
'Polar Low' News
Chile Stocks End Week Lower In Line With US Market - Wall Street Journal
news.google.com
Chile Stocks End Week Lower In Line With US Market

Wall Street Journal

Gainers included department store chain La Polar (LAPOLAR.SN), which rose 2.5% to CLP1,890.30, and casino and hotel operator Enjoy, which climbed 1.9% to ...



and more »
Google News Search: Polar low,
Fri Jul 17 06:33:06 2009
'Polar Low' Blogs
WowWee Alive Polar Bear Cub Plush Robotic Toy in White
buyplushtoys.blogspot.com
WowWee Alive Polar Bear Cub Plush Robotic Toy in White

atom

Sat, 14 Nov 2009 02:01:00 GM

Buy . Low. Price From Here Now. Introducing the first friends in a new series of lifelike cubs from WowWee Alive. With super-soft fur and a totally realistic look, this cuddly cub gives little . polar. bear lovers a totally true-to-life ...

Google Blogs Search: Polar low,
Mon Nov 16 14:53:54 2009
[Hide]▲