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Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet.
In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. 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, Jupiter, 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.
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone.
Hurricane Alberto was among the longest-lived tropical cyclones on record in the Atlantic Ocean. The third tropical cyclone, first named storm, and first hurricane of the 2000 Atlantic hurricane season, Alberto developed near the western coast of Africa from a tropical wave on August 3. Initially a tropical depression, it strengthened into Tropical Storm Alberto early on August 4. While briefly turning westward on August 6, Alberto attained hurricane status. The cyclone continued to track west-northwestward, and by early the following day, reached an initial peak with winds of 90 mph (150 km/h). Shortly thereafter, Alberto re-curved northwestward and began encountering increased wind shear. As a result, Alberto weakened back to a tropical storm on August 9. However, the system quickly re-strengthened as winds became more favorable, and early on August 10, Alberto became a hurricane again. The storm gradually curved northward and north-northeastward between August 11 and August 12; Alberto attained its peak intensity with winds of 125 mph (205 km/h) during that time.
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 systems form under areas of wind divergence that occur in the upper levels of the atmosphere. The formation process of a low-pressure area is known as cyclogenesis. In meteorology, atmospheric divergence aloft occurs in two kinds of places:
The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner. Tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere.
The 1990 Atlantic hurricane season was the most active Atlantic hurricane season since 1969, with a total of 14 named storms. The season also featured eight hurricanes, one of which intensified into a major hurricane. It officially began on June 1, 1990, and lasted until November 30, 1990. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. However, tropical cyclogenesis can occur prior to the start of the season, as demonstrated with Tropical Depression One, which formed in the Caribbean Sea on May 24.
A tropical wave, in and around the Atlantic Ocean, is 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. Tropical waves form in the easterly flow along the equator-ward side of the subtropical ridge or belt of high air 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.
The 1990 Pacific hurricane season was a very active season which observed 21 named storms within the basin. The season also produced the fourth highest ACE index value on record. The season was officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. However, the formation of tropical cyclones is possible at any time of the year, as illustrated in 1990 by the formation of the season's first named storm, Hurricane Alma, on May 12. At the time, this was the earliest formation of a tropical storm on record in the eastern Pacific
A trough is an elongated region of relatively low atmospheric pressure without a closed isobaric contour that would define it as a low pressure area. Since low pressure implies a low height on a pressure surface, troughs and ridges refer to features in an identical sense as those on a topographic map.
A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for almost one-third of the world's annual tropical cyclones. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, central, and western. The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Hawaii, the Philippines and Hong Kong. While the RSMC names each system, the main name list itself is coordinated among 18 countries that have territories threatened by typhoons each year.
The geography of South America contains many diverse regions and climates. Geographically, South America is generally considered a continent forming the southern portion of the landmass of the Americas, south and east of the Colombia–Panama border by most authorities, or south and east of the Panama Canal by some. South and North America are sometimes considered a single continent or supercontinent, while constituent regions are infrequently considered subcontinents.
Hurricane Karen was a hurricane of non-tropical origin that formed in October of the 2001 Atlantic hurricane season. It developed out of the interaction between a cold front and an upper level trough on October 10 located to the south of Bermuda, and quickly strengthened as an extratropical storm. The storm passed near Bermuda on October 12, producing hurricane-force winds on the island. It then organized, becoming a subtropical cyclone on the 12th and a tropical cyclone on the 13th. Karen strengthened to reach 80 mph (130 km/h) winds as a Category 1 hurricane on the Saffir-Simpson Hurricane Scale, and after weakening over cooler waters, it made landfall on Nova Scotia as a tropical storm. It quickly became extratropical.
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.
The meteorological history of Hurricane Ivan, the longest tracked tropical cyclone of the 2004 Atlantic hurricane season, lasted from late August through late September. The hurricane developed from a tropical wave that moved off the coast of Africa on August 31. Tracking westward due to a ridge, favorable conditions allowed it to develop into Tropical Depression Nine on September 2 in the deep tropical Atlantic Ocean. The cyclone gradually intensified until September 5, when it underwent rapid deepening and reached Category 4 status on the Saffir-Simpson Hurricane Scale; at the time Ivan was the southernmost major North Atlantic hurricane on record.
The 2001–02 South Pacific cyclone season was a below-average year in which only five named storms formed or entered the South Pacific basin. It began on November 1, 2001 and ended on April 30, 2002. These dates conventionally delimit the period of each year when most tropical cyclones form in the southern Pacific Ocean east of 160°E. Additionally, the regional tropical cyclone operational plan defines a tropical cyclone year separately from a tropical cyclone season, and the "tropical cyclone year" runs from July 1, 2001 to June 30, 2002. The season's sixteen tropical depressions existed within these dates with the first developing on November 29 and the last dissipating on April 22.
An upper tropospheric cyclonic vortex is a vortex, or a circulation with a definable center, that usually moves slowly from east-northeast to west-southwest and is prevalent across Northern Hemisphere's warm season. Its circulations generally do not extend below 6,080 metres (19,950 ft) in altitude, as it is an example of a cold-core low. A weak inverted wave in the easterlies is generally found beneath it, and it may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of circulation at ground level. In rare cases, a warm-core cyclone can develop in its associated convective activity, resulting in a tropical cyclone and a weakening and southwest movement of the nearby upper tropospheric cyclonic vortex. Symbiotic relationships can exist between tropical cyclones and the upper level lows in their wake, with the two systems occasionally leading to their mutual strengthening. When they move over land during the warm season, an increase in monsoon rains occurs.
A Gulf of California moisture surge, or simply gulf surge, is a meteorological event where a pulse of high humidity air is pushed up the Gulf of California. Gulf surges bring moisture to southern Arizona during the North American Monsoon. Prior to the 1970s, the consensus of meteorologists was the moisture that fueled the central and southern Arizona monsoon resulted from the movement of the Bermuda High to a more south and west position, which in turn transported water vapor to the region from the Gulf of Mexico. However, operational meteorologists in the 1970s described episodic surges of moisture that infiltrated the area that was thought to originate in the Gulf of California. It was noted that these episodes were likely to be associated with a convective system near the tip of the Baja peninsula such as a tropical cyclone or an easterly wave.
The Tropical Atlantic SST Dipole refers to a cross-equatorial sea surface temperature (SST) pattern that appears dominant on decadal timescales. It has a period of about 12 years, with the SST anomalies manifesting their most pronounced features around 10–15 degrees of latitude off of the Equator. It is also referred to as the interhemispheric SST gradient or the Meridional Atlantic mode.
Hurricane Pali was the earliest-forming Pacific hurricane on record, and the first Pacific hurricane to occur in January since Hurricane Ekeka in 1992. The first tropical cyclone of the 2016 Pacific hurricane season, Pali originated as an area of low pressure within a persistent trough, near the equator on January 6, 2016. Deep convection gradually built up around the center of the disturbance as the system curved northward, before it organized into a tropical depression on the next day, making the system the earliest recorded tropical cyclone in the Pacific hurricane basin. The system quickly reached tropical storm status and was named Pali. For the next couple of days, Pali slowly moved northward, while slowly curving towards the west, and the storm strengthened somewhat before weakening, due to the presence of wind shear. On January 10, Pali slowly turned eastward and proceeded to re-strengthen, as wind shear diminished.
References
- 1 2 Marcel Leroux (2001). The Meteorology and Climate of Tropical Africa. Springer. pp. 138–139. ISBN 978-3-540-42636-3 . Retrieved 5 February 2011.
- ↑ B. Pu and K. H. Cook (2008). Dynamics of the Low-Level Westerly Jet Over West Africa. American Geophysical Union, Fall Meeting 2008, abstract #A13A-0229. Retrieved on 8 March 2009.
- ↑ Kerry H. Cook. Generation of the African Easterly Jet and Its Role in Determining West African Precipitation. Retrieved on 8 May 2008.
- ↑ Chris Landsea. AOML Frequently Asked Questions. Subject: A4) What is an easterly wave ? Retrieved on 8 May 2008.
- ↑ Rostami, M., Zeitlin, V., 2021, Instabilities of low-latitude easterly jets in the presence of moist convection and topography and related cyclogenesis, in a simple atmospheric model. Geophysical & Astrophysical Fluid Dynamics, DOI:10.1080/03091929.2021.1959574.
- ↑ Climate Prediction Center (November 1997). "Figure 7". National Oceanic and Atmospheric Administration . Retrieved 5 February 2011.
