A polar low is a mesoscale, short-lived atmospheric low pressure system (depression) that is found over the ocean areas poleward of the main

polar front In meteorology, the polar front is the weather front boundary between the polar cell and the Ferrel cell around the 60° latitude, near the polar regions, in both hemispheres. At this boundary a sharp gradient in temperature occurs between thes ...

in both the Northern and Southern Hemispheres, as well as the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it ...

. The systems usually have a horizontal length scale of less than and exist for no more 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 platform An oil platform (also called an oil rig, offshore platform, oil production platform, etc.) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms w ...

s. 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).

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 polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

during the winter, such as the

Norwegian Sea The Norwegian Sea (; ; ) is a marginal sea, grouped with either the Atlantic Ocean or the Arctic Ocean, northwest of Norway between the North Sea and the Greenland Sea, adjoining the Barents Sea to the northeast. In the southwest, it is separate ...

Barents Sea The Barents Sea ( , also ; , ; ) is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territorial waters.World Wildlife Fund, 2008. It was known earlier among Russi ...

Labrador Sea The Labrador Sea (; ) is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelf, continental shelves to the southwest, northwest, and northeast. It connects to the north with Baffi ...

and

Gulf of Alaska The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') 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 ...

; however, polar lows also have been found in the

and the

Sea of Okhotsk The Sea of Okhotsk; Historically also known as , or as ; ) is a marginal sea of the western Pacific Ocean. It is located between Russia's Kamchatka Peninsula on the east, the Kuril Islands on the southeast, Japan's island of Hokkaido on the sou ...

. Polar lows dissipate rapidly when they make landfall.

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

systems tend to be weaker than their northern counterparts since the air-sea temperature differences around the continent are generally smaller. Still, vigorous polar lows can be found over the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean, generally taken to be south of 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...

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 An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

’, 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

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 (often called baroclinicity) of a stratified fluid is a measure of how misaligned the gradient of pressure is from the gradient of density in a fluid. In meteorology, a baroclinic flow is one in which the dens ...

, and these can have the appearance of small frontal depressions. At the other extreme are the polar lows with extensive

cumulonimbus Cumulonimbus () is a dense, towering, vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water va ...

clouds, which are often associated with cold pools in the mid- to upper-

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

. During winter, when cold-core lows with temperatures in the mid-levels of the troposphere reach move over open waters, deep convection forms which allows polar low development to become possible (polar lows usually occur with cold air outbreaks).

Frequency and impact

Although cyclonic activity is most prevalent in the Eurasian Arctic with approximately 15 lows per winter, polar lows also occur in

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

and the

Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...

Arctic. Polar lows occur in the extended winter season, with seldom occurrences during the summer. They are not well studied and seldom destructive as they typically take place in sparsely populated areas. The only infrastructure damage that occurs as a direct result of a polar low is to oil and gas rigs present throughout the Antarctic Ocean (sometimes known as the

). Some cargo and shipping vessels are also affected, although there are minimal or no reports of losses in recent years as the result of a polar low. Despite the more equatorward location, numerous polar lows can form over the

every year, due to the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) contributed by the

cold-core low A cold-core low, also known as an upper level low or cold-core cyclone, is a cyclone aloft which has an associated cold pool of air residing at high altitude within the Earth's troposphere, without a frontal structure. It is a low pressure syste ...

aloft and the warm Tsushima Current. They would bring severe impacts to

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

owing to the proximity to populous regions, with strong winds and heavy snowfall. On December 28, 1986, seven passenger cars of a railway train were blown from the Amarube Viaduct due to a polar low, causing six deaths.

Forecasting

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 Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to weather forecasting, predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of comput ...

models are only just getting the horizontal and vertical resolution to represent these systems.

References

External links

Polar Lows
by MetEd

* ttps://web.archive.org/web/20050831020251/http://www.meteo.uni-bonn.de/mitarbeiter/GHeinemann/eplwg/eplwg.htm European Polar Lows Working Group
Understanding Polar Lows - BBC Weather A-Z
{{Arctic topics Types of cyclone Barents Sea Sea of Japan