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Encyclopedia > Polar low
Polar low over the Barents Sea on February 27, 1987
Polar low over the Barents Sea on February 27, 1987

A polar low is a small-scale, short-lived atmospheric low pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than 1,000 km and exist for less than a couple of days. They are part of the larger class of mesoscale 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. Image File history File links Polar_low. ... Image File history File links Polar_low. ... Location of the Barents Sea. ... February 27 is the 58th day of the year in the Gregorian Calendar. ... 1987 (MCMLXXXVII) was a common year starting on Thursday of the Gregorian calendar. ... A large low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that nature abhors a vacuum. ... In meteorology, a Polar Front is the boundary between the polar cell and the Ferrel cell in each hemisphere. ... The term mesoscale is a size scale referring to weather systems smaller than synoptic scale systems but larger than storm-scale cumulus systems. ...

Polar lows have been referred to by many other terms, such as comma cloud, mesocyclone, 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 gale force (17 m/s).

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 during the winter, such as the Norwegian Sea, Barents Sea, Sea of Japan, and Gulf of Alaska. Polar lows dissipate rapidly when they make landfall. Antarctic 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 red line indicates the 10°C isotherm in July, commonly used to define the Arctic region border Satellite image of the Arctic surface The Arctic is the region around the Earths North Pole, opposite the Antarctic region around the South Pole. ... The Norwegian Sea (Norwegian: Norskehavet) is part of the North Atlantic Ocean northwest of Norway, located between the North Sea (i. ... Location of the Barents Sea. ... The Sea of Japan (East Sea) is a marginal sea of the western Pacific Ocean. ... 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. ... Greek ἀνταρκτικός, opposite the arctic) is a continent surrounding the Earths South Pole. ...

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’, 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. Eye of Category 4 Hurricane Isabel seen from the International Space Station on September 15, 2003 The eye is a region of mostly calm weather found at the center of strong tropical cyclones. ...

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, and these can have the appearance of small frontal depressions. At the other extreme are the polar lows with extensive cumulonimbus clouds, which are often associated with cold pools in the mid- to upper-troposphere. Baroclinic Instability is a fluid dynamic instability which helps to understand some important features of the so-called large scale waves in the mid-latitude atmosphere. ... Cumulonimbus cloud in central Oklahoma. ... Atmosphere diagram showing the mesosphere and other layers. ...

Polar lows are very difficult to forecast and a nowcasting 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. Modern weather predictions aid in timely evacuations and potentially save lives and property damage Weather map of Europe, 10 December 1887 Weather forecasting is the application of current technology and science to predict the state of the atmosphere for a future time and a given location. ...

See also

Cyclones and Anticyclones of the world
v  d  e
Extratropical - Meso-scale - Polar - Polar low - Subtropical - Tropical

Radar image of a tropical cyclone in the northern hemisphere. ... In meteorology, an anticyclone (i. ... A fictitious synoptic chart of an extratropical cyclone affecting the UK & Ireland. ... This article or section may be confusing for some readers, and should be edited to be clearer or more simplified. ... Polar cyclones (also known as Arctic Cyclones) are vast areas of low pressure. ... A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. ... This article is very long Some browsers may have difficulty rendering this article. ...

Further reading

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

External links

  • European Polar Lows Working Group
  • Polar Low Forecasting by MetEd

  Results from FactBites:
Polar low - Wikipedia, the free encyclopedia (4108 words)
Polar lows are similar in behavior and size to tropical cyclones, although generally much shorter lived.
Polar lows are typically several hundred kilometres in diameter, generally have strong winds (although generally not at hurricane intensity) and last one to two days on average.
Occlusions from mature synoptic-scale lows are a favoured mechanism between the British Isles and southern Greenland, while primary polar lows are generally confined to the area north of Iceland across to the Barents Sea.
Polar low boven zuidelijke Noordzee (1296 words)
Aanvankelijk viel het nog niet mee om tot een sluitende definitie te komen van een polar low.
Het polar low is van al deze depressies in de koude lucht het felst en gevaarlijkst, maar desondanks, - of misschien wel juist daardoor, - het meest geliefd bij veel meteorologen en weerliefhebbers.
Het oog van het polar low van 30 januari was in de ochtend boven de Noordzee zichtbaar op satellietbeelden ; na wisselwerking van de depressie met het land van Oost-Engeland, werd het oog snel minder markant.
  More results at FactBites »



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