The
South Pacific Convergence Zone (SPCZ), a reverse-oriented
monsoon troughThe monsoon trough or those portions of the Intertropical Convergence Zone within a monsoon region, is depicted by a line on a weather map showing the locations of minimum sea level pressure, and is a convergence zone between the wind patterns of the southern and northern hemispheres...
, 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 ZoneThe Intertropical Convergence Zone is a term that is used to describe the North-East and South-East trade wind convergence. Convectively active portions of the ITCZ are known as the monsoon trough...
(ITCZ) which lies just south of the Equator, but can be more extratropical in nature, especially east of the
DatelineA dateline is a brief piece of text included in news articles that describes where and when the story 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 troughThe monsoon trough or those portions of the Intertropical Convergence Zone within a monsoon region, is depicted by a line on a weather map showing the locations of minimum sea level pressure, and is a convergence zone between the wind patterns of the southern and northern hemispheres...
.
This zone occurs where the southeast trades from transitory
anticycloneIn meteorology, an anticyclone is a weather phenomenon in which there is a descending movement of the air, and with surface systems, higher than average atmospheric pressure over the part of the planet's surface. Effects of surface-based anticyclones include clearing skies as well as cooler,...
s to the south meet with the semipermanent easterly flow from the eastern South Pacific anticyclone.
The
South Pacific Convergence Zone (SPCZ), a reverse-oriented
monsoon troughThe monsoon trough or those portions of the Intertropical Convergence Zone within a monsoon region, is depicted by a line on a weather map showing the locations of minimum sea level pressure, and is a convergence zone between the wind patterns of the southern and northern hemispheres...
, 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 ZoneThe Intertropical Convergence Zone is a term that is used to describe the North-East and South-East trade wind convergence. Convectively active portions of the ITCZ are known as the monsoon trough...
(ITCZ) which lies just south of the Equator, but can be more extratropical in nature, especially east of the
DatelineA dateline is a brief piece of text included in news articles that describes where and when the story 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 troughThe monsoon trough or those portions of the Intertropical Convergence Zone within a monsoon region, is depicted by a line on a weather map showing the locations of minimum sea level pressure, and is a convergence zone between the wind patterns of the southern and northern hemispheres...
.
Position
This zone occurs where the southeast trades from transitory
anticycloneIn meteorology, an anticyclone is a weather phenomenon in which there is a descending movement of the air, and with surface systems, higher than average atmospheric pressure over the part of the planet's surface. Effects of surface-based anticyclones include clearing skies as well as cooler,...
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
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
, 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 IslandsThe Solomon Islands is a country in Melanesia, east of Papua New Guinea, consisting of nearly one thousand islands. Together they cover a land mass of 28,400 square kilometres . The capital is Honiara, located on the island of Guadalcanal.The Solomon Islands are believed to have been...
through
FijiFiji , officially the Republic of the Fiji Islands , is an island nation in the South Pacific Ocean east of Vanuatu, west of Tonga and south of Tuvalu. The country comprises an archipelago of about 322 islands, of which 106 are permanently inhabited, and 522 islets...
,
SamoaSamoa , officially the Independent State of Samoa , is a country governing 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 Savai'i...
, and
TongaTonga , officially the Kingdom of Tonga , an archipelago in the South Pacific Ocean, comprises 169 islands, 36 of which are inhabited, and stretches over a distance of about 800 kilometres in a north-south line...
. 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
ENSOEnsō 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 enlightenment, strength, elegance, the Universe, and the void; it can also symbolize...
.
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)