A convergence zone in

meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...

is a region in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

where two prevailing flows meet and interact, usually resulting in distinctive weather conditions. This causes a mass accumulation that eventually leads to a vertical movement and to the formation of

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

s and

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

. Large-scale convergence, called synoptic-scale convergence, is associated with weather systems such as baroclinic troughs,

low-pressure area 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 (such as cloudy, windy, with possibl ...

s, and cyclones. The large-scale convergence zone formed over the equator, the Intertropical Convergence Zone, has condensed and intensified as a result of the global increase in temperature. Small-scale convergence will give phenomena from isolated cumulus clouds to large areas of thunderstorms. The inverse of convergence is divergence.

Large scale

An example of a convergence zone is the Intertropical Convergence Zone (ITCZ), a low pressure area which girdles the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

at the

Equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...

.Waliser, D.E.; Jiang, X. (2015). "Tropical Meteorology and Climate: Intertropical Convergence Zone". ''Reference Module in Earth Systems and Environmental Sciences'' 6(2): 121-131. Another example is the South Pacific convergence zone that extends from the western

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

toward

French Polynesia )Territorial motto: ( en, "Great Tahiti of the Golden Haze") , anthem = , song_type = Regional anthem , song = "Ia Ora 'O Tahiti Nui" , image_map = French Polynesia on the globe (French Polynesia centered).svg , map_alt = Location of French ...

The Intertropical Convergence Zone is the result of the northeasterly trade winds and southeasterly trade winds converging in an area of high latent heat and low pressure. As the two trade winds converge, the cool, dry air collects moisture from the warm ocean and rises, contributing to cloud formation and precipitation. The low pressure area that is created by the movement of the trade winds acts as a

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...

, drawing in the cooler, dry air from high pressure areas (divergence zones), creating a convection cell commonly known as the Hadley Cell.

Sea surface temperature Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air ma ...

is directly related to the position of the Sun or the location of the " energy flux equator," thus the ITCZ shifts corresponding to the seasons. Due to the position of the Sun, the sea surface temperature near the equator (30°S to 30°N), during an

equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears zenith, directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" ...

, is higher than any other latitudes. During the summer solstice in the Northern Hemisphere (June 21), the ITCZ is shifted north, following the position of the Sun.Schneider, Tapio; Bischoff, Tobias; Haug, Gerald H. (2014). "Migrations and dynamics of the Intertropical Convergence Zone." ''Nature'' 513: 45–53. The ITCZ is shifted farther south during the

winter solstice The winter solstice, also called the hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the winte ...

(in the Northern Hemisphere), when the solar radiation is focused at 23.5°S.

Mesoscale

Convergence zones also occur at a smaller scale. Convergence lines form rows of showers or thunderstorms over a more local area. Sea breezes

colliding In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

can trigger development of a convergence line. The heavy rain caused in a short period of time can cause severe flooding. Some examples are the

Puget Sound Convergence Zone The Puget Sound Convergence Zone (PSCZ) is a meteorological phenomenon that occurs over Puget Sound in the U.S. state of Washington. It is formed when the large-scale air flow splits around the Olympic Mountains and then converges over Puget Sound. ...

which occurs in the

Puget Sound Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected m ...

region in the U.S. state of Washington; Mohawk–Hudson convergence in the U.S. state of New York; th
Elsinore Convergence Zone
in the U.S. state of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

; the Brown Willy effect which can be generated when south-westerly winds blow over Bodmin Moor in

Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlan ...

; and the Pembrokeshire Dangler which can form when northerly winds blow down the

Irish Sea The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the Ce ...

. Flooding in Boscastle, Cornwall, England in August 2004 was the result of thunderstorms developing on a convergence line.

References

{{DEFAULTSORT:Convergence Zone Atmosphere Gliding technology