WESTERN PACIFIC INDEX (WP) |
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Western Pacific Index (WP)The Western Pacific (WP) is a primary mode of low-frequency variability in the North Pacific. The pioneering analysis by Wallace and Gutzler (1981) identified the five major teleconnection patterns in the 500-hPa geopotential height field. A study by Barnston and Livezey (1987) extracted the WP variability using rotated principal component analysis (RPCA) applied to hemispheric 700-hPa geopotential height anomalies. The WP pattern emerged as the second or third leading mode of variability in the 1950–84 record of monthly anomalies. During winter and spring, the pattern consists of a north–south dipole of anomalies, with one center located over the Kamchatka Peninsula and another center of opposite sign extending over portions of Southeast Asia and the Subtropical Western North Pacific. Therefore, strong positive or negative phases of this pattern reflect pronounced zonal and meridional shifts in the location and intensity of the regional jet stream. The vertical structure of the WP was examined by Hsu and Wallace (1985). Its pattern exhibits a distinct vertical configuration over the Pacific Ocean and the Rocky Mountains. Over the Pacific, the structure is essentially barotropic, whereas along the eastern slopes of the Rocky Mountains it becomes strongly baroclinic. Subsequent studies have shown that the WP is closely related to the low-frequency pattern known as the North Pacific Oscillation (NPO), primarily observed near the surface. Both patterns feature opposing centers of action across the North Pacific and influence the position of the jet stream, also affecting the development and movement of extratropical cyclones. This WP–NPO connection was detailed by Linkin and Nigam (2008). The interaction between the WP and ENSO is also well documented. El Niño and La Niña events can modulate the intensity of the WP because changes in tropical convection during these episodes generate atmospheric responses that propagate into the midlatitudes. The strength of this connection depends on the type of ENSO and on the location of warming in the equatorial Pacific, as discussed by Houk et al. (2016). The WP also influences tropical cyclone activity in the Western Pacific. Phase shifts in the pattern modify vertical wind shear and the dynamic environment of the basin, affecting both the number and the tracks of typhoons. These effects were documented by Choi & Moon (2012). |
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The WP (West Pacific) teleconnection pattern is a prominent mode of variability in the midlatitudes of the Northern Hemisphere, especially during winter. Its operational definition follows the methodology established by the Climate Prediction Center (CPC/NOAA), based on Rotated Principal Component Analysis (RPCA) applied to standardized 500-hPa geopotential height anomalies. The dataset used is the NCEP/NCAR Reanalysis. (CPC — Teleconnection Pattern Calculations)
The calculation procedure follows the steps below:
The modern formulation of the WP pattern follows the conceptual foundations established in classical studies on atmospheric teleconnections:
Although the WP can be simplified as a meridional dipole over the western Pacific, the CPC’s RPCA-based methodology is more robust because it accounts for the full variability of the 500-hPa anomaly field, ensuring seasonal consistency and statistical stability. (CPC — Teleconnection Pattern Calculations)
| SOUZA, C. A. de; REBOITA, M. S. Ferramenta para o Monitoramento dos Padrões de Teleconexão na América do Sul. Terrae Didatica, Campinas, SP, v. 17, n. 00, p. e02109, 2021. DOI: 10.20396/td.v17i00.8663474 |
