Tropical Upper Tropospheric Trough
Encyclopedia
A tropical upper tropospheric trough (TUTT), also known as the mid-oceanic trough, is a trough
situated in upper-level (at about 200 hPa) tropics
. Its formation is usually caused by the intrusion of energy and wind from the mid-latitudes into the tropics. It can also develop from the inverted trough adjacent to an upper level anticyclone. TUTTs are different from mid-latitude troughs in the sense that they are maintained by subsidence warming near the tropopause
which balances radiational cooling. When strong, they can present a significant vertical wind shear
to the tropics and subdue tropical cyclogenesis
. When upper cold lows
break off from their base, they tend to retrograde and force the development, or enhance, surface troughs and tropical waves to their east. Under special circumstances, they can induce thunderstorm activity and lead to the formation of tropical cyclone
s.
, and west-northwest to east-southeast across oceans of the Southern Hemisphere
. In the South Pacific, it stretches from near the equator at the 175th meridian west
to the east-southeast near 30N 105W, offshore the western South America
n coast. In the South Atlantic, the TUTT extends from near the equator at the 75th meridian west
east-southeast to 30N 15W, offshore the western coast of southern Africa
. In the North Atlantic, the TUTT is oriented from 35N 30W (south of the Azores
) to 22N 95W (the southern Gulf of Mexico
). In the North Pacific, it stretches from 35N 145W (offshore western North America
) to 22N 135E, offshore the northeast coast of the Philippines
.
by providing additional forced ascent near the storm center and an efficient outflow channel in the upper troposphere
. This is most likely near its most westward and equatorward periphery.
. Upper cyclones and upper troughs which trail tropical cyclones can cause additional outflow channels and aid in their intensification process. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.
Trough (meteorology)
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked...
situated in upper-level (at about 200 hPa) tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
. Its formation is usually caused by the intrusion of energy and wind from the mid-latitudes into the tropics. It can also develop from the inverted trough adjacent to an upper level anticyclone. TUTTs are different from mid-latitude troughs in the sense that they are maintained by subsidence warming near the tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
which balances radiational cooling. When strong, they can present a significant vertical wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
to the tropics and subdue tropical cyclogenesis
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes 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 mid-latitude cyclogenesis occurs...
. When upper cold lows
Upper tropospheric cyclonic vortex
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 in altitude, as it is an example...
break off from their base, they tend to retrograde and force the development, or enhance, surface troughs and tropical waves to their east. Under special circumstances, they can induce thunderstorm activity and lead to the formation of tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
s.
Location
The TUTT is elongated from east-northeast to west-southwest across oceans of the Northern HemisphereNorthern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
, and west-northwest to east-southeast across oceans of the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. In the South Pacific, it stretches from near the equator at the 175th meridian west
175th meridian west
The meridian 175° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....
to the east-southeast near 30N 105W, offshore the western South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
n coast. In the South Atlantic, the TUTT extends from near the equator at the 75th meridian west
75th meridian west
The meridian 75° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Atlantic Ocean, the Caribbean Sea, South America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....
east-southeast to 30N 15W, offshore the western coast of southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. In the North Atlantic, the TUTT is oriented from 35N 30W (south of the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
) to 22N 95W (the southern Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
). In the North Pacific, it stretches from 35N 145W (offshore western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
) to 22N 135E, offshore the northeast coast of the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
.
Effects within the tropics
TUTTs sometimes brings a large amount of vertical wind shear over tropical disturbances in the deep tropics and cyclones and thus hinder their development. However, there are cases that TUTTs assist the genesis and intensification of tropical cyclonesTropical cyclogenesis
Tropical cyclogenesis is the term that describes 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 mid-latitude cyclogenesis occurs...
by providing additional forced ascent near the storm center and an efficient outflow channel in the upper troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
. This is most likely near its most westward and equatorward periphery.
Upper lows pinching off from their base
Under specific circumstances, upper cold lows can break off from the base of the TUTT. These upper tropospheric cyclonic vortices usually move slowly from east-northeast to west-southwest, and generally do not extend below 20,000 feet in altitude. A weak inverted wave in the easterlies is generally found underneath them, and they may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of a surface vortex. In rare cases, they become warm-core, resulting in the vortex becoming a tropical cycloneTropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
. Upper cyclones and upper troughs which trail tropical cyclones can cause additional outflow channels and aid in their intensification process. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.
External links
- FAQs on Hurricanes, Typhoons And Tropical Cyclones
- Definition of TUTT in Traditional Chinese
- Tropical textbook : from trades to cyclone (2 vols). The chapter 8.4 deals with TUTT. Florent Beucher, Météo-France, 897 pp., 25 mai 2010, ISBN : 978-2-11-099391-5.