Azores High

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The Azores High (Portuguese : Anticiclone dos Açores) also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of 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 southern Europe, and to a lesser extent, eastern North America. The aridity of the Sahara Desert and the summer drought of the Mediterranean Basin is due to the large-scale subsidence and sinking motion of air in the system. In its summer position (the Bermuda High), the high is centered near Bermuda, and creates a southwest flow of warm tropical air toward the East Coast of the United States. In summer, the Azores-Bermuda High is strongest. The central pressure hovers around 1024 mbar (hPa).

Portuguese language Romance language that originated in Portugal

Portuguese is a Western Romance language originating in the Iberian Peninsula. It is the sole official language of Portugal, Brazil, Cape Verde, Guinea-Bissau, Mozambique, Angola, and São Tomé and Príncipe. It also has co-official language status in East Timor, Equatorial Guinea and Macau in China. As the result of expansion during colonial times, a cultural presence of Portuguese and Portuguese creole speakers are also found in Goa, Daman and Diu in India; in Batticaloa on the east coast of Sri Lanka; in the Indonesian island of Flores; in the Malacca state of Malaysia; and the ABC islands in the Caribbean where Papiamento is spoken, while Cape Verdean Creole is the most widely spoken Portuguese-based Creole. A Portuguese-speaking person or nation may be referred to as "Lusophone" in both English and Portuguese.

Subtropics

The subtropics are geographic and climate zones located roughly between the tropics at latitude 23.5° and temperate zones north and south of the Equator.

High-pressure area region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment

A high-pressure area, high or anticyclone is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment.

Contents

Tropical wave formation on the Atlantic Ocean. Tropical waves.jpg
Tropical wave formation on the Atlantic Ocean.

This high-pressure block exhibits anticyclonic nature, circulating the air clockwise. Due to this direction of movement, African eastern waves are impelled along the southern periphery of the Azores High away from coastal West Africa towards the Caribbean, Central America, or the Bahamas, favouring tropical cyclogenesis, especially during the hurricane season.

Block (meteorology) term in meteorology for large-scale patterns in the atmospheric pressure field that are nearly stationary, effectively “blocking” or redirecting migratory cyclones

Blocks in meteorology are large-scale patterns in the atmospheric pressure field that are nearly stationary, effectively “blocking” or redirecting migratory cyclones. They are also known as blocking highs or blocking anticyclones. These blocks can remain in place for several days or even weeks, causing the areas affected by them to have the same kind of weather for an extended period of time. In the Northern Hemisphere, extended blocking occurs most frequently in the spring over the eastern Pacific and Atlantic Oceans.

Anticyclone opposite to a cyclone

An anticyclone is a weather phenomenon defined by the United States 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 cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm core lows such as tropical cyclones, due to descending cool air from the backside of upper troughs such as polar highs, or from large scale sinking such as the subtropical ridge. The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.

Clockwise one that proceeds in the same direction as a clocks hands

Two-dimensional rotation can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite sense of rotation or revolution is counterclockwise (CCW) or anticlockwise (ACW).

Variations

Research into global warming suggests that it may be intensifying the Bermuda High in some years, independently of oscillations such as ENSO, leading to more precipitation extremes across the Southeastern United States. Latitudinal displacement of the ridge is also occurring, and computer models depict more westward expansion of the anticyclone in the future. [1] [2] However, during the winter of 20092010, the Azores High was smaller, displaced to the northeast and weaker than usual, allowing sea surface temperatures in the Central Atlantic to increase quickly. [3]

Global warming rise in the average temperature of the Earths climate system and its related effects

Global warming is a long-term rise in the average temperature of the Earth's climate system, an aspect of climate change shown by temperature measurements and by multiple effects of the warming. The term commonly refers to the mainly human-caused observed warming since pre-industrial times and its projected continuation, though there were also much earlier periods of global warming. In the modern context the terms global warming and climate change are commonly used interchangeably, but climate change includes both global warming and its effects, such as changes to precipitation and impacts that differ by region. Many of the observed warming changes since the 1950s are unprecedented in the instrumental temperature record, and in historical and paleoclimate proxy records of climate change over thousands to millions of years.

Southeastern United States Region

The Southeastern United States is broadly, the eastern portion of the Southern United States, and the southern portion of the Eastern United States. It comprises at least a core of states on the lower Atlantic seaboard and eastern Gulf Coast. Expansively, it includes everything south of the Mason-Dixon line, the Ohio River and the 36°30' parallel, and as far west as Arkansas and Louisiana. There is no official U.S. government definition of the region, though various agencies and departments use different definitions.

Sea surface temperature Water temperature close to the oceans surface

Sea surface temperature (SST) is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a short distance of the shore. Localized areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures are known to be a cause of tropical cyclogenesis over the Earth's oceans. Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi-decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.

See also

Hadley cell A global scale tropical atmospheric circulation feature

The Hadley cell, named after George Hadley, is a global scale tropical atmospheric circulation that features air rising near the Equator, flowing poleward at a height of 10 to 15 kilometers above the earth’s surface, descending in the subtropics, and then returning equatorward near the surface. This circulation creates the trade winds, tropical rain-belts and hurricanes, subtropical deserts and the jet streams.

Cold front leading edge of a cooler mass of air

A cold front is the leading edge of a cooler mass of air, replacing at ground level a warmer mass of air, which lies within a fairly sharp surface trough of low pressure. It forms in the wake of an extratropical cyclone, at the leading edge of its cold air advection pattern, which is also known as the cyclone's dry conveyor belt circulation. Temperature changes across the boundary can exceed 30 °C (54 °F). When enough moisture is present, rain can occur along the boundary. If there is significant instability along the boundary, a narrow line of thunderstorms can form along the frontal zone. If instability is less, a broad shield of rain can move in behind the front, which increases the temperature difference across the boundary. Cold fronts are stronger in the fall and spring transition seasons and weakest during the summer.

Related Research Articles

Cyclone large scale air mass that rotates around a strong center of low pressure

In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.

1963 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1963 Atlantic hurricane season featured one of the deadliest tropical cyclones on record in the Atlantic basin: Hurricane Flora. The season officially began on June 15, and lasted until November 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. It was a near-average season in terms of tropical storms, with a total of nine named storms. The first system, Hurricane Arlene, developed between Cape Verde and the Lesser Antilles on July 31. The storm later impacted Bermuda, where strong winds resulted in about $300,000 (1963 USD) in damage. Other storms such as hurricanes Beulah and Debra, as well as an unnamed tropical storm, did not impact land. During the month of September, Hurricane Cindy caused wind damage and flooding in Texas, leaving three deaths and approximately $12.5 million in damage. Hurricane Edith passed through the Lesser Antilles and the eastern Greater Antilles, causing 10 deaths and about $43 million in damage, most of which occurred on Martinique.

1973 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1973 Atlantic hurricane season was the first season to use the Saffir–Simpson hurricane scale, a scale developed in 1971 by Herbert Saffir and Robert Simpson to rate the intensity of tropical cyclones. The season produced 24 tropical and subtropical cyclones, of which only 8 reached storm intensity, 4 became hurricanes, and only 1 reached major hurricane status. Although more active than the 1972 season, 1973 brought few storms of note. Nearly half of the season's storms affected land, one of which resulted in severe damage.

1975 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1975 Atlantic hurricane season featured the first tropical storm to be upgraded to a hurricane based solely on satellite imagery – Hurricane Doris. The season officially began on June 1 and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The season was near average, with nine tropical storms forming, of which six became hurricanes. Three of those six became major hurricanes, which are Category 3 or higher on the Saffir–Simpson scale. The first system, Tropical Depression One, developed on June 24. Tropical Storm Amy in July caused minor beach erosion and coastal flooding from North Carolina to New Jersey, and killed one person when a ship capsized offshore North Carolina. Hurricane Blanche brought strong winds to portions of Atlantic Canada, leaving about $6.2 million (1975 USD) in damage. Hurricane Caroline brought high tides and flooding to northeastern Mexico and Texas, with two drownings in the latter.

1976 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1976 Atlantic hurricane season featured only one fully tropical storm throughout both the Caribbean Sea and the Gulf of Mexico, a rare occurrence. The season officially began on June 1 and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. However, the first system, a subtropical storm, developed in the Gulf of Mexico on May 21, several days before the official start of the season. The system spawned nine tornadoes in Florida, resulting in about $628,000 (1976 USD) in damage, though impact was minor otherwise. The season was near average, with ten tropical storm forming, of which six became hurricanes. Two of those six became major hurricanes, which are Category 3 or higher on the Saffir–Simpson scale.

1978 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1978 Atlantic hurricane season was the last Atlantic hurricane season to use an all-female naming list. The hurricane season officially began on June 1, and ended on November 30. It was an above average season due to a subsiding El Niño. The first storm, a subtropical storm, developed unusually early – on January 18 – and dissipated five days later without causing any damage. At the end of July and early August, short-lived Tropical Storm Amelia caused extensive flooding in Texas after dropping as much as 48 in (1,200 mm) of rain. There were 33 deaths and $110 million (1978 USD) in damage. Tropical Storm Bess and Hurricane Cora resulted in only minor land impacts, while the latter was attributed to one fatality.

1979 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1979 Atlantic hurricane season was the first season to include both male and female names, as well as the common six-year rotating lists of tropical cyclone names. The season officially began on June 1, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. It was slightly below average, with nine systems reaching tropical storm intensity. The first system, an unnumbered tropical depression, developed north of Puerto Rico on June 9. Two days later, Tropical Depression One formed and produced severe flooding in Jamaica, with 40 deaths and about $27 million (1979 USD) in damage. Tropical Storm Ana caused minimal impact in the Lesser Antilles. Hurricane Bob spawned tornadoes and produced minor wind damage along the Gulf Coast of the United States, primarily in Louisiana, while the remnants caused flooding, especially in Indiana. Tropical Storm Claudette caused extensive flooding, due to torrential rainfall. There were two deaths and damaged totaled $750 million.

1989 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1989 Atlantic hurricane season was an average season with 11 named storms. The season officially began on June 1, and ended on November 30. The first storm, Tropical Depression One, developed on June 15, and dissipated two days later without effects on land. Later that month, Tropical Storm Allison caused severe flooding, especially in Texas and Louisiana. Tropical Storm Barry, Tropical Depressions Six, Nine, and Thirteen, and Hurricanes Erin and Felix caused negligible impact. Hurricane Gabrielle and Tropical Storm Iris caused light effects on land, with the former resulting in nine fatalities from rip currents offshore the East Coast of the United States and Atlantic Canada, while the latter produced minor flooding in the United States Virgin Islands.

Tropical wave type of atmospheric trough

Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics, causing areas of cloudiness and thunderstorms. West-moving waves can also form from the tail end of frontal zones in the subtropics and tropics, and may be referred to as easterly waves, but these waves are not properly called tropical waves; they are a form of inverted trough sharing many characteristics with fully tropical waves. All tropical waves form in the easterly flow along the equatorward side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical cyclones in the north Atlantic and northeastern Pacific basins. A tropical wave study is aided by Hovmöller diagrams, a graph of meteorological data.

1950 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1950 Atlantic hurricane season was the first year in the Atlantic hurricane database (HURDAT) that storms were given names in the Atlantic basin. Names were taken from the Joint Army/Navy Phonetic Alphabet, with the first named storm being designated "Able", the second "Baker", and so on. It was an active season with sixteen tropical storms, with eleven of them developing into hurricanes. Six of these hurricanes were intense enough to be classified as major hurricanes—a denomination reserved for storms that attained sustained winds equivalent to a Category 3 or greater on the present-day Saffir–Simpson scale. One storm, the twelfth of the season, was unnamed and was originally excluded from the yearly summary, and three additional storms were discovered in re-analysis. The large quantity of strong storms during the year yielded, prior to modern reanalysis, what was the highest seasonal accumulated cyclone energy (ACE) of the 20th century in the Atlantic basin; 1950 held the seasonal ACE record until broken by the 2005 Atlantic hurricane season. However, later examination by researchers determined that several storms in the 1950 season were weaker than thought, leading to a lower ACE than assessed originally.

1926 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1926 Atlantic hurricane season featured the highest number of major hurricanes at the time. At least eleven tropical cyclones developed during the season, all of which intensified into a tropical storm and eight further strengthened into hurricanes. Six hurricanes deepened into a major hurricane, which is Category 3 or higher on the modern-day Saffir–Simpson hurricane wind scale. The first system, the Nassau hurricane, developed near the Lesser Antilles on July 22. Moving west-northwest for much of its duration, the storm struck or brush several islands of the Lesser and Greater Antilles. However, the Bahamas later received greater impact. At least 287 deaths and $7.85 million (1926 USD) in damage was attributed to this hurricane. The next cyclone primarily affected mariners in and around the Maritimes of Canada, with boating accidents and drownings resulting in between 55 and 58 fatalities. In late August, the third hurricane brought widespread impact to the Gulf Coast of the United States, especially Louisiana. Crops and buildings suffered $6 million (1926 USD) in damage and there were 25 people killed. The next three storms left relatively little to no damage on land.

Hurricane Alice (December 1954) Category 1 Atlantic hurricane in December 1954 and January 1955

Hurricane Alice is the only known Atlantic hurricane to span two calendar years and one of only two named Atlantic tropical cyclones, along with Tropical Storm Zeta of 2005, to do so. The twelfth tropical cyclone and the eighth hurricane of the 1954 Atlantic hurricane season, Alice developed on December 30, 1954 from a trough of low pressure in the central Atlantic Ocean in an area of unusually favorable conditions. The storm moved southwestward and gradually strengthened to reach hurricane status. After passing through the Leeward Islands on January 2, 1955, Alice reached peak winds of 90 mph (150 km/h) before encountering cold air and turning to the southeast. It dissipated on January 6 over the southeastern Caribbean Sea.

Extratropical cyclone type of cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.

Hurricane Arlene (1987) Category 1 Atlantic hurricane in 1987

Hurricane Arlene was a long-lived tropical cyclone that moved eastward in an erratic fashion in the northern Atlantic Ocean in mid-August 1987. The first named storm of the 1987 Atlantic hurricane season, Arlene formed out of an area of low pressure associated with a decaying frontal system along the North Carolina coastline, Arlene tracked in a general eastward direction across the Atlantic Ocean, taking an erratic track with several curves. On August 13, the storm brushed Bermuda as a weak tropical storm before continuing out to sea. On August 20, the storm briefly stalled before becoming a hurricane two days later. Early on August 24, the storm transitioned into an extratropical cyclone over the far north Atlantic before curving southeast and dissipating near the Iberian Peninsula on August 26.

Tropical Storm Grace (2009) Atlantic tropical storm in 2009

Tropical Storm Grace holds the record for being the farthest northeast forming tropical cyclone in the Atlantic basin. The seventh named storm of the slightly below average 2009 Atlantic hurricane season, Grace formed from an extratropical cyclone over the Azores on October 4. It strengthened to attain peak sustained winds of 65 mph (100 km/h) and developed an eye-like feature, although cold sea surface temperatures inhibited the development of thunderstorm activity near the center. The storm lost its tropical characteristics on October 6, though the remnants merged with a separate system near the British Isles.

2010 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 2010 Atlantic hurricane season was the first in a group of three very active Atlantic hurricane seasons. It is tied alongside 1887, 1995, 2011, and 2012 with 19 tropical storms, the third highest count in recorded history. It featured 12 hurricanes, tied with 1969 for the second highest total. Only the quintessential 2005 season saw more activity. The overall tropical cyclone count in the Atlantic exceeded that in the West Pacific for only the second time on record. The season officially began on June 1 and ended on November 30, dates that conventionally delimit the period during each year when tropical cyclone formation is most likely. The first cyclone, Alex intensified into the first June hurricane since Allison in 1995. The month of September featured eight named storms, tying 2002 and 2007 for the record. October featured five hurricanes, just short of the record set in 1870. Finally, Hurricane Tomas became the latest hurricane on record to move through the Windward Islands in late October. Activity was represented with an accumulated cyclone energy (ACE) value of 165 units, which was the eleventh highest value on record at the time.

Timeline of the 2011 Atlantic hurricane season

The 2011 Atlantic hurricane season was well above average in the number of tropical cyclones that formed, at nineteen. It was also the first time that the first eight tropical cyclones of the season failed to attain hurricane status. Although Tropical Storm Arlene formed on June 28, the season officially began on June 1 and ended on November 30, dates that conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin. The season's final storm, Tropical Storm Sean, dissipated on November 11.

Centers of action are extensive and almost stationary low-pressure areas or anticyclones 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

American Meteorological Society

The American Meteorological Society (AMS) is the premier scientific and professional organization in the United States promoting and disseminating information about the atmospheric, oceanic, and hydrologic sciences. Its mission is to advance the atmospheric and related sciences, technologies, applications, and services for the benefit of society.

  1. Lucas, Tim. "Variable southeast summer rainfall linked to climate change". Duke University. EurekAlert!. Archived from the original on 30 October 2010. Retrieved 29 October 2010.
  2. Li, Wenhong; Laifang Li; Rong Fu; Yi Deng; Hui Wang (October 4, 2010). "Changes to the North Atlantic Subtropical High and Its Role in the Intensification of Summer Rainfall Variability in the Southeastern United States". American Meteorological Society. 24 (5): 1499–1506. Bibcode:2011JCli...24.1499L. CiteSeerX   10.1.1.211.2720 . doi:10.1175/2010JCLI3829.1. ISSN   1520-0442.
  3. Publications, RMS. "2009 Atlantic Hurricane Season Review and 2010 Season Outlook" (PDF). Risk Management Solutions. RMS Catastrophe Response. Archived (PDF) from the original on 8 October 2010. Retrieved 29 October 2010.

Coordinates: 34°00′00″N30°00′00″W / 34.0000°N 30.0000°W / 34.0000; -30.0000

Geographic coordinate system Coordinate system

A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector. A common choice of coordinates is latitude, longitude and elevation. To specify a location on a plane requires a map projection.