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South Pacific Convergence Zone (SPCZ)

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Category: Weather Weather
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary
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Tag(s) Climatic Phenomena

Description

The South Pacific Convergence Zone (SPCZ) is a persistent band of cloudiness and storms, a 200-400 km broad zone that originates in Southeast Asia and stretches southeast to French Polynesia and the Cook Islands. The SPCZ is the largest and most persistent spur of the ITCZ. It is also the only spur that does not result from heating over land during the summer. The SPCZ is most active in the southern hemisphere summer, but it is present year-round.

South Pacific Convergence Zone

Impact on weather in the South Pacific

The SPCZ can affect the precipitation on Polynesian islands in the southwest Pacific Ocean, so it is important to understand how the SPCZ behaves with large-scale, global climate phenomenon, such as the ITCZ, El Niño–Southern Oscillation, and the Interdecadal Pacific oscillation (IPO), a portion of the Pacific decadal oscillation. Rainfall varies greatly by season in the Central South Pacific sub-region: approximately 75% of annual rainfall occurs from November to April, when the SPCZ is located about halfway between Western Samoa and Fiji. During the dry season, the SPCZ moves out of the area, and often becomes weak or inactive

Influence of trade winds, El Nino and the West Pacific Warm Pool

The SPCZ occurs where the southeast trades from transitory anticyclones to the south meet with the semipermanent easterly flow from the eastern South Pacific anticyclone. The SPCZ exists in summer and winter but can change its orientation and location. It is often distinct from the ITCZ over Australia, 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 through Vanuatu, Fiji, Samoa, and Tonga. 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.

The SPCZ is fueled by moisture from the west pacific warm pool(also referred to as the warm western Pacific basin), and is most active from October to April (during the Southern Hemisphere summer) due to propagated monsoon activity from India.

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