South Pacific convergence zone
Encyclopedia
The South Pacific Convergence Zone (SPCZ), a reverse-oriented monsoon trough
Monsoon trough
The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

, is a band of low-level convergence, cloudiness and precipitation extending from the west Pacific warm pool south-eastwards towards French Polynesia. It is a portion of the Intertropical Convergence Zone
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

 (ITCZ) which lies just south of the Equator, but can be more extratropical in nature, especially east of the Dateline
Dateline
A dateline is a brief piece of text included in news articles that describes where and when the story occurred, or was written or filed, though the date is often omitted. In the case of articles reprinted from wire services, the distributing organization is also included...

. It is considered the largest and most important piece of the ITCZ, and has the least dependence upon heating from a nearby landmass during the summer than any other portion of the monsoon trough
Monsoon trough
The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

.

Position

This zone occurs where the southeast trades from transitory anticyclone
Anticyclone
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"...

s to the south meet with the semipermanent easterly flow from the eastern South Pacific anticyclone. The SPCZ exists in summer and winter, with approximately the same orientation and location. It is often distinct from the ITCZ over Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, but at times they become one continuous zone of convergence. The location of the SPCZ is affected by ENSO and Interdecadal Pacific Oscillation conditions. It generally stretches from the Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...

 through Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...

, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...

, and Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...

. Low level convergence along this band forms cloudiness as well as showers and thunderstorms. Thunderstorm activity, or convection, within the band is dependent upon the season, as the more equatorward portion is most active in the Southern Hemisphere summer, and the more poleward portion is most active during transition seasons of fall and spring. The convergence zone shifts east or west depending on the existence of El Niño, or the phase of ENSO
Enso
Ensō is a Japanese word meaning "circle" and a concept strongly associated with Zen. Ensō is one of the most common subjects of Japanese calligraphy even though it is a symbol and not a character. It symbolizes the Absolute enlightenment, strength, elegance, the Universe, and the void; it can...

.

Related oceanography

At its southeast edge, the circulation around the feature forces a salinity gradient in the ocean, with fresher and warmer waters of the western Pacific lying to its west. Cooler and saltier waters lie to its east.

Progression

The South Pacific Convergence Zone moves northeast during El Niño and southwest during La Niña events. The same movement takes place during positive IPO and negative IPO phases respectively. West of about 140 W, both the SOI and IPO strongly influence the SPCZ latitude, but farther east only the SOI is a significant factor. Only near 170 W is there any indication of an interaction between the two factors. (Folland et al., 2002)

See also

  • ENSO
    Enso
    Ensō is a Japanese word meaning "circle" and a concept strongly associated with Zen. Ensō is one of the most common subjects of Japanese calligraphy even though it is a symbol and not a character. It symbolizes the Absolute enlightenment, strength, elegance, the Universe, and the void; it can...

  • Monsoon trough
    Monsoon trough
    The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

  • 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...

  • 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...

  • Coral bleaching
    Coral bleaching
    Coral bleaching is the loss of intracellular endosymbionts through either expulsion or loss of algal pigmentation.The corals that form the structure of the great reef ecosystems of tropical seas depend upon a symbiotic relationship with unicellular flagellate protozoa, called zooxanthellae, that...


World Wide Web


Tropical textbook : from trade winds to cyclone (2 vol), 897 pp., Florent Beucher, 25 mai 2010, Météo-France, ISBN 978-2-11-099391-5
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