Aleutian Low

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A large Aleutian Low in the Gulf of Alaska on October 24, 2011 Aleutian low 24 october 2011.jpg
A large Aleutian Low in the Gulf of Alaska on October 24, 2011

The Aleutian Low is a semi-permanent low-pressure system located near the Aleutian Islands in the Bering Sea during the Northern Hemisphere winter. It is a climatic feature centered near the Aleutian Islands measured based on mean sea-level pressure. It is one of the largest atmospheric circulation patterns in the Northern Hemisphere and represents one of the "main centers of action in atmospheric circulation." [1]

Contents

Classification

The Aleutian Low is characterized by heavily influencing the path and strength of cyclones. Extratropical cyclones which form in the sub-polar latitudes in the North Pacific typically slow down and reach maximum intensity in the area of the Aleutian Low. Tropical cyclones that form in the tropical and equatorial regions of the Pacific can veer northward and get caught in the Aleutian Low. This is usually seen in the later summer months. Both the November 2011 Bering Sea cyclone and the November 2014 Bering Sea cyclone were extratropical cyclones that had dissipated and restrengthened when the systems entered the Aleutian Low region. The storms are remembered and marked as two of the strongest storms to impact the Bering Sea and Aleutian Islands with pressure dropping below 950 mb in each system. The magnitude of the low pressure creates an extreme atmospheric disturbance, which can cause other significant shifts in weather. Following the November 2014 Bering Sea cyclone, a huge cold wave, November 2014 North American cold wave, hit the US bringing record breaking low temperatures to many states.

Effects

The low serves as an atmospheric driver for low-pressure systems, post-tropical cyclones and their remnants and can generate strong storms that impact Alaska and Canada. Intensity of the low is strongest in the winter and almost completely dissipates in the summer. The circulation pattern is measured based on averages of synoptic features help mark the locations of cyclones and their paths over a given time period. However, there is significant variability in these measurements. The circulation pattern shifts during the Northern Hemisphere summer when the North Pacific High takes over and breaks apart the Aleutian Low. This high-pressure circulation pattern strongly influences tropical cyclone paths. The presence of the Eurasian and North American continents prevent a continuous belt of low pressure from developing in the Northern Hemisphere sub-polar latitudes, which would mirror the circumpolar belt of low pressure and frequent storms in the Southern Ocean. [2] However, the presence of the continents disrupts this motion, and the subpolar belt of low pressure is well developed only in the North Pacific (the Aleutian Low) and the North Atlantic (the Icelandic Low, which is located between Greenland and Iceland [3] ). The strength of the Aleutian Low has been proposed as a driving factor in determining primary production in the water column and, in turn, impacting the catch in the salmon fishery. [4] [5]

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<span class="mw-page-title-main">Subtropical cyclone</span> Cyclonic storm with tropical and extratropical characteristics

A subtropical cyclone is a weather system that has some characteristics of both tropical and extratropical cyclones.

<span class="mw-page-title-main">Low-pressure area</span> Area with air pressures lower than adjacent areas

In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather, while high-pressure areas are associated with lighter winds and clear skies. Winds circle anti-clockwise around lows in the northern hemisphere, and clockwise in the southern hemisphere, due to opposing Coriolis forces. Low-pressure systems form under areas of wind divergence that occur in the upper levels of the atmosphere (aloft). The formation process of a low-pressure area is known as cyclogenesis. In meteorology, atmospheric divergence aloft occurs in two kinds of places:

<span class="mw-page-title-main">Westerlies</span> Prevailing winds from the west

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<span class="mw-page-title-main">Typhoon Tip</span> Pacific typhoon in 1979

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<span class="mw-page-title-main">Fujiwhara effect</span> Meteorological phenomenon involving two cyclones circling each other

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<span class="mw-page-title-main">1997 Pacific typhoon season</span> Typhoon season in the Western Pacific Ocean

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<span class="mw-page-title-main">1981 Pacific typhoon season</span>

The 1981 Pacific typhoon season was a slightly above average season that produced 29 tropical storms, 13 typhoons and two intense typhoons. The season ran throughout 1981, though most tropical cyclones typically develop between May and October. The season's first named storm, Freda, developed on March 12 while the final storm, Lee, dissipated on December 29. Tropical cyclones only accounted for 12 percent of the rainfall in Hong Kong this season, the lowest percentage for the protectorate since 1972.

<span class="mw-page-title-main">1970 Pacific typhoon season</span>

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<span class="mw-page-title-main">1961 Pacific typhoon season</span>

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<span class="mw-page-title-main">Dvorak technique</span> Subjective technique to estimate tropical cyclone intensity

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<span class="mw-page-title-main">Tropical cyclogenesis</span> Development and strengthening of a tropical cyclone in the atmosphere

Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.

<span class="mw-page-title-main">Extratropical cyclone</span> Type of cyclone

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<span class="mw-page-title-main">Tropical cyclone</span> Type of rapidly rotating storm system

A tropical cyclone is a rapidly rotating storm system with a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn or more.

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Explosive cyclogenesis is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 millibars (0.71 inHg) or more in 24 hours. This is a predominantly maritime, winter event, but also occurs in continental settings. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is entirely different from that of tropical cyclones, bomb cyclones can produce winds of 74 to 95 mph, the same order as the first categories of the Saffir–Simpson scale, and yield heavy precipitation. Even though only a minority of bomb cyclones become this strong, some weaker ones can also cause significant damage.

<span class="mw-page-title-main">Inflow (meteorology)</span> Meteorological term for flow of a fluid into a large collection of itself

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<span class="mw-page-title-main">Braer Storm</span> Intense extratropical cyclone 1993 over the northern Atlantic Ocean

The Braer Storm was the most intense extratropical cyclone ever recorded over the northern Atlantic Ocean. Developing as a weak frontal wave on 8 January 1993, the system moved rapidly northeast. The combination of the absorption of a second low-pressure area to its southeast, a stronger than normal sea surface temperature differential along its path, and the presence of a strong jet stream aloft led to a rapid strengthening of the storm, with its central pressure falling to an estimated 914 hPa on 10 January. Its strength was well predicted by forecasters in the United Kingdom, and warnings were issued before the low initially developed.

<span class="mw-page-title-main">November 2014 Bering Sea cyclone</span>

The November 2014 Bering Sea cyclone was the most intense extratropical cyclone ever recorded in the Bering Sea, which formed from a new storm developing out of the low-level circulation that separated from Typhoon Nuri, which soon absorbed the latter. The cyclone brought gale-force winds to the western Aleutian Islands and produced even higher gusts in other locations, including a 97 miles per hour (156 km/h) gust in Shemya, Alaska. The storm coincidentally occurred three years after another historic extratropical cyclone impacted an area slightly further to the east.

Centers of action are extensive and almost stationary low or high pressure areas which control the movement of atmospheric disturbances over a large area. This does not mean that the position of the center is constant over a specific area but that the monthly atmospheric pressure corresponds to a high or a low pressure.

References

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  2. Sinclair, Mark (1997). "Objective identification of cyclones and their circulation intensity, and climatology". Weather and Forecasting. 12 (3): 595–612. Bibcode:1997WtFor..12..595S. doi: 10.1175/1520-0434(1997)012<0595:OIOCAT>2.0.CO;2 .
  3. Serreze, Mark; Carse, Fiona; Barry, Roger G; Rogers, Jeffery C (1997). "Icelandic Low cyclone activity: Climatological features, linkages with the NAO, and relationships with recent changes in the Northern Hemisphere circulation". Journal of Climate. 10 (3): 455. Bibcode:1997JCli...10..453S. doi: 10.1175/1520-0442(1997)010<0453:ilcacf>2.0.co;2 .
  4. Gargett, Ann E. (1997). "The optimal stability 'window': a mechanism underlying decadal fluctuations in North Pacific salmon stocks?". Fisheries Oceanography. 6 (2): 109–117. Bibcode:1997FisOc...6..109G. doi:10.1046/j.1365-2419.1997.00033.x. ISSN   1365-2419.
  5. Gargett, Ann E. (1997). "Physics to Fish: Interactions Between Physics and Biology on a Variety of Scales". Oceanography. 10 (3): 128–131. doi: 10.5670/oceanog.1997.05 . ISSN   1042-8275. JSTOR   43924818.