Azores High

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).

Tropical waves
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.

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 2009–2010, 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]

See also

References

  • "The Azores High". WeatherOnline Weather facts. Retrieved 2006-11-19.
  • "Azores high". Glossary of Meteorology. American Meteorological Society. Archived from the original on 26 October 2006. Retrieved 2006-11-19.
  • "Bermuda high". Glossary of Meteorology. American Meteorological Society. Archived from the original on 19 October 2006. Retrieved 2006-11-19.
  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″N 30°00′00″W / 34.0000°N 30.0000°W

Anticyclone

An anticyclone (that is, opposite to a cyclone) 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 .

Anticyclonic storm

An anticyclonic storm is a weather storm where winds around the storm flow in the direction opposite to that of the flow about a region of low pressure.

Atlantic hurricane

An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, usually between the months of June and November. A hurricane differs from a cyclone or typhoon only on the basis of location. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean.Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph (34 knots, 17 m/s, 63 km/h), while hurricanes have one-minute maximum sustained winds exceeding 74 mph (64 knots, 33 m/s, 119 km/h). Most North Atlantic tropical storms and hurricanes form between June 1 and November 30. The United States National Hurricane Center monitors the basin and issues reports, watches, and warnings about tropical weather systems for the North Atlantic Basin as one of the Regional Specialized Meteorological Centers for tropical cyclones, as defined by the World Meteorological Organization.In recent times, tropical disturbances that reach tropical storm intensity are named from a predetermined list. Hurricanes that result in significant damage or casualties may have their names retired from the list at the request of the affected nations in order to prevent confusion should a subsequent storm be given the same name. On average, in the North Atlantic basin (from 1966 to 2009) 11.3 named storms occur each season, with an average of 6.2 becoming hurricanes and 2.3 becoming major hurricanes (Category 3 or greater). The climatological peak of activity is around September 10 each season.In March 2004, Catarina was the first hurricane-intensity tropical cyclone ever recorded in the Southern Atlantic Ocean. Since 2011, the Brazilian Navy Hydrographic Center has started to use the same scale of the North Atlantic Ocean for tropical cyclones in the South Atlantic Ocean and assign names to those which reach 35 kn (65 km/h; 40 mph).

Barahona, Dominican Republic

Barahona, also known as Santa Cruz de Barahona, is the main city of the Barahona Province, in the south of the Dominican Republic. It is one of the most important cities on the island, with a very active port and many ecotourism attractions. The city is also a centre of sugar production and industry.

Barotropic vorticity equation

The barotropic vorticity equation assumes the atmosphere is nearly barotropic, which means that the direction and speed of the geostrophic wind are independent of height. In other words, there is no vertical wind shear of the geostrophic wind. It also implies that thickness contours (a proxy for temperature) are parallel to upper level height contours. In this type of atmosphere, high and low pressure areas are centers of warm and cold temperature anomalies. Warm-core highs (such as the subtropical ridge and the Bermuda-Azores high) and cold-core lows have strengthening winds with height, with the reverse true for cold-core highs (shallow Arctic highs) and warm-core lows (such as tropical cyclones).

A simplified form of the vorticity equation for an inviscid, divergence-free flow (solenoidal velocity field), the barotropic vorticity equation can simply be stated as

where D/Dt is the material derivative and

is absolute vorticity, with ζ being relative vorticity, defined as the vertical component of the curl of the fluid velocity and f is the Coriolis parameter

where Ω is the angular frequency of the planet's rotation (Ω = 0.7272×10−4 s−1 for the earth) and φ is latitude.

In terms of relative vorticity, the equation can be rewritten as

where β = f/y is the variation of the Coriolis parameter with distance y in the north–south direction and v is the component of velocity in this direction.

In 1950, Charney, Fjørtoft, and von Neumann integrated this equation (with an added diffusion term on the right-hand side) on a computer for the first time, using an observed field of 500 hPa geopotential height for the first timestep. This was one of the first successful instances of numerical weather prediction.

Climate of Hungary

The 'climate of Hungary is characterised by its position. Hungary is in the eastern part of Central Europe, roughly equidistant from the Equator and the North Pole, more than 1,000 kilometres (600 mi) from either and about 1,000 kilometres from the Atlantic Ocean. It is also at least 500 kilometres (300 mi) from any main branches of the Mediterranean Sea.

Its climate, like its whole geography, is as the result of environmental changes during the Holocene Era.

Hungary's climate is the result of the interaction of two major climate systems: the continental climate and the Oceanic climate. The influence of both these systems are felt across the country at different times, which means, that the weather is very changeable.

Climate of Manitoba

Because of its location in the centre of the North American continent, the climate of Manitoba is extreme. In general, temperatures and precipitation decrease from south to north, and precipitation also decreases from east to west. Since Manitoba is far removed from the moderating influences of both mountain ranges and large bodies of water, and because of the generally flat landscape in many areas, it is exposed to numerous weather systems throughout the year, including cold Arctic high-pressure air masses that settle in from the northwest, usually during the months of January and February. In the summer, the air masses often come out of the southern United States, as the stronger Azores High ridges into the North American continent, the more warm, humid air is drawn northward from the Gulf of Mexico, generally during the months of July or August.

High-pressure area

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.

Winds within high-pressure areas flow outward from the higher pressure areas near their centers towards the lower pressure areas further from their centers. Gravity adds to the forces causing this general movement, because the higher pressure compresses the column of air near the center of the area into greater density – and so greater weight compared to lower pressure, lower density, and lower weight of the air outside the center.

However, because the planet is rotating underneath the atmosphere, and frictional forces arise as the planetary surface drags some atmosphere with it, the air flow from center to periphery is not direct, but is twisted due to the Coriolis effect, or the merely apparent force that arise when the observer is in a rotating frame of reference. Viewed from above this twist in wind direction is in the same direction as the rotation of the planet.

The strongest high-pressure areas are associated with cold air masses which push away out of polar regions during the winter when there is less sun to warm neighboring regions. These Highs change character and weaken once they move further over relatively warmer water bodies.

Somewhat weaker but more common are high-pressure areas caused by atmospheric subsidence, that is, areas where large masses of cooler drier air descend from an elevation of 8 to 15 km after the lower temperatures have precipitated out the water vapor.

Many of the features of Highs may be understood in context of middle- or meso-scale and relatively enduring dynamics of a planet's atmospheric circulation. For example, massive atmospheric subsidences occur as part of the descending branches of Ferrel cells and Hadley cells. Hadley cells help form the subtropical ridge, steer tropical waves and tropical cyclones across the ocean and is strongest during the summer. The subtropical ridge also helps form most of the world's deserts.

On English-language weather maps, high-pressure centers are identified by the letter H. Weather maps in other languages may use different letters or symbols.

Hurricane Alley

Hurricane Alley is an area of warm water in the Atlantic Ocean stretching from the west coast of northern Africa to the east coast of Central America and Gulf Coast of the Southern United States. Many hurricanes form within this area. The sea surface temperature of the Atlantic in Hurricane Alley has grown slightly warmer over the past decades. A particularly warm summer in 2005 led climate scientists to begin studying whether this trend would lead to an increase in hurricane activity. See Effects of Climate Change below.

Hurricane Danielle (1998)

Hurricane Danielle resulted in minor damage throughout its duration as a tropical cyclone in late August and early September 1998. The fourth named storm and second hurricane of the annual hurricane season, Danielle originated from a tropical wave that emerged off the western coast of Africa on August 21. Tracking generally west-northwestward, the disturbance was initially disorganized; under favorable atmospheric conditions, shower and thunderstorm activity began to consolidate around a low-pressure center. Following a series of satellite intensity estimates, the system was upgraded to Tropical Depression Four during the pre-dawn hours of August 24, and further to Tropical Storm Danielle that afternoon. Moving around the southern periphery of the Azores High located in the northeastern Atlantic, quick intensification to hurricane status occurred early on August 25. By 0600 UTC the following day, Danielle reached an initial peak intensity of 105 mph (165 km/h), a Category 2 hurricane. Increased wind shear from a nearby trough encroached on further development later that day, and subsequently led to slight weakening. By 1200 UTC on August 27, despite continued unfavorable conditions, Danielle reached a second peak intensity equal to the first. Weakening once ensued late on August 27 in addition to the days following, and Danielle was a low-end Category 1 hurricane by August 31 as its forward speed slowed.

As the cyclone reached the western periphery of the ridge that steered it across the Atlantic for much of its existence, it began yet another period of intensification, and once again attained a peak intensity as a Category 2 hurricane. Passing northwest of Bermuda, Danielle weakened to Category 1 hurricane strength, but for a final time intensified into a 105 mph (165 km/h) tropical cyclone thereafter. As the cyclone passed over increasingly cool sea surface temperatures and became intertwined in a baroclinic zone, it began to undergo an extratropical transition. At 0000 UTC on September 4, Danielle was no longer considered a tropical cyclone, despite retaining hurricane-force winds. Several days later, the remnants of Danielle merged with a larger extratropical low and became indistinguishable. As a tropical cyclone, it produced heavy rainfall in Puerto Rico and the Lesser Antilles, leading to flooding. Tropical storm-force winds were observed in Bermuda even though the cyclone passed well northwest of the island. During Danielle's transition to an extratropical cyclone, it produced light rain and led to minor beach erosion in Newfoundland. The larger extratropical low that merged with the system resulted in large waves off the coast of the United Kingdom, leading to major beach erosion and coastal flooding. Overall, no fatalities were reported with the system and it caused an estimated $50,000 (1998 USD) in damage.

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 circulation of the Northern Hemisphere, associated with frequent cyclone activity. It forms one pole of the North Atlantic oscillation, the other being the Azores High.

Kalahari High

The Kalahari High is an anticyclone that forms in winter over the interior of southern Africa, replacing a summer trough. It is part of the subtropical ridge system and the reason the Kalahari is a desert. It is the descending limb of a Hadley cell.

Mesoscale meteorology

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.

Vertical velocity often equals or exceeds horizontal velocities in mesoscale meteorological systems due to nonhydrostatic processes such as buoyant acceleration of a rising thermal or acceleration through a narrow mountain pass.

Multiple-vortex tornado

A multiple-vortex tornado is a tornado that contains several vortices (called subvortices or suction vortices) rotating around, inside of, and as part of the main vortex. The only times multiple vortices may be visible are when the tornado is first forming or when condensation and debris are balanced such that subvortices are apparent without being obscured. They can add over 100 mph to the ground-relative wind in a tornado circulation, and are responsible for most (if not all) cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths.

North American High

The North American High (also Canadian High/Anticyclone, sometimes in Europe Greenland High/Anticyclone) is an impermanent high-pressure area or anticyclone created by a formative process that occurs when cool or cold dry air settles over North America. In summer it is replaced with an Arctic Low, or if it moves to continental land, a North American Low.

North American Highs move eastwards across the continent, often in the company of one or more low-pressure cells or cyclones. Its cold, dense air does not extend usually above 3 km (1.9 mi), lower than the Canadian Rockies. Sometimes, in winter it breaks free and passes over the Rockies and brings a cold front into Southwestern United States and Mexico, freezing crops and bringing snow into Mexico's mountains as far south as Jalisco. The high’s usual location east of the Rockies shelters it from the relatively warm Pacific Ocean and helps it maintain its strength. The average January sea level pressure at its centre is about 1,020 millibars (30.12 inches of mercury). The Canadian high often moves southeastward until it eventually reaches the Atlantic Ocean, where it merges with the Azores high. In the summer the Canadian high circulates cool, dry air to the United States east of the Rockies and parts of southern Canada.

The North American High is akin to the Siberian High of Eurasia, but it is much smaller, and it has much less influence, merely affecting the weather of the Northern Hemisphere. The sea-level pressure (atmospheric pressure) rarely, if ever, exceeds 1055.0 millibars (1055.0 hectopascals)(hPa)(SI).

Often, in the winter months, cool or cold dry air settles over the land in the vicinity of the Great Basin where it builds into a high-pressure cell or anticyclone that moves across the United States with a cold front on its leading edge. After reaching the Atlantic Ocean, the moist environment brings on changes of the qualities of the air and the dissipation of the high-pressure cell or anticyclone as the cold air warms and becomes humid.

In Europe, a portion of the North American/Canadian high usually over Greenland called the Greenland high which settles over Greenland affects northern European weather and may merge with the Scandinavian High.

North Atlantic oscillation

The North Atlantic Oscillation (NAO) is a weather phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and location of storm tracks across the North Atlantic. It is part of the Arctic oscillation, and varies over time with no particular periodicity.The NAO was discovered through several studies in the late 19th and early 20th centuries. Unlike the El Niño-Southern Oscillation phenomenon in the Pacific Ocean, the NAO is a largely atmospheric mode. It is one of the most important manifestations of climate fluctuations in the North Atlantic and surrounding humid climates.The North Atlantic Oscillation is closely related to the Arctic oscillation (AO) (or Northern Annular Mode (NAM)), but should not be confused with the Atlantic Multidecadal Oscillation (AMO).

Rapid intensification

Rapid intensification is a meteorological condition that occurs when a tropical cyclone intensifies dramatically in a short period of time. The United States National Hurricane Center (NHC) defines rapid intensification as an increase in the maximum 1-min sustained winds of a tropical cyclone of at least 30 knots (35 mph; 55 km/h) in a 24-hour period.

Timeline of the 2006 Atlantic hurricane season

The 2006 Atlantic hurricane season was the first since 2001 in which no hurricanes made landfall in the United States, and the first since 1994 that no tropical cyclones formed during October. This timeline documents all the storm formations, strengthening, weakening, landfalls, extratropical transitions, as well as dissipation. The season officially began on June 1, 2006, and lasted until November 30. The timeline includes information which was not operationally released, meaning that information from post-storm reviews by the National Hurricane Center, such as information about a storm that was not operationally warned on, have been included.

The 2006 Atlantic hurricane season was significantly less active than the previous year's Atlantic hurricane season. Following the intense activity of 2005, forecasts predicted that the 2006 season would be only slightly less active. However, activity was slowed by a rapidly forming El Niño event in 2006, the presence of the Saharan Air Layer over the tropical Atlantic, and the steady presence of a robust secondary high-pressure area to the Azores high centered on Bermuda. There were no tropical cyclones after October 2. The calendar year 2006 also saw Tropical Storm Zeta, which arose in December 2005 and persisted until early January, only the second event on record that a storm spanned two calendar years in the Atlantic. The storm can be considered a part of the 2005 and 2006 seasons, although it occurred outside the June 1 – November 30 windows during which most Atlantic basin tropical cyclones form.

Whirlwind

A whirlwind is a weather phenomenon in which a vortex of wind (a vertically oriented rotating column of air) forms due to instabilities and turbulence created by heating and flow (current) gradients. Whirlwinds occur all over the world and in any season.

Concepts
Anticyclone
Cyclone

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