Zonal Winds in the Central Equatorial Pacific and El Niño

Luther, Douglas S.; Harrison, D. E.; Knox, Robert A.

doi:10.1126/science.222.4621.327

Cited by 150 publications

(99 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The increased occurrence of WWBs prior to and during most El Niño events has been observed and noted in the past (e.g., Delcroix et al 1993;Keen 1982;Luther et al 1983;Vecchi and Harrison 2000;Verbickas 1998). We begin here with an analysis of high-resolution satellite observations suggesting that WWBs are indeed affected by ENSO.…”

Section: Observational Evidence Of Wwb Modulation By Ensomentioning

confidence: 85%

See 1 more Smart Citation

Westerly Wind Bursts: ENSO’s Tail Rather than the Dog?

2005

View full text Add to dashboard Cite

Westerly wind bursts (WWBs) in the equatorial Pacific occur during the development of most El Niño events and are believed to be a major factor in ENSO's dynamics. Because of their short time scale, WWBs are normally considered part of a stochastic forcing of ENSO, completely external to the interannual ENSO variability. Recent observational studies, however, suggest that the occurrence and characteristics of WWBs may depend to some extent on the state of ENSO components, implying that WWBs, which force ENSO, are modulated by ENSO itself.Satellite and in situ observations are used here to show that WWBs are significantly more likely to occur when the warm pool is extended eastward. Based on these observations, WWBs are added to an intermediate complexity coupled ocean-atmosphere ENSO model. The representation of WWBs is idealized such that their occurrence is modulated by the warm pool extent. The resulting model run is compared with a run in which the WWBs are stochastically applied. The modulation of WWBs by ENSO results in an enhancement of the slow frequency component of the WWBs. This causes the amplitude of ENSO events forced by modulated WWBs to be twice as large as the amplitude of ENSO events forced by stochastic WWBs with the same amplitude and average frequency. Based on this result, it is suggested that the modulation of WWBs by the equatorial Pacific SST is a critical element of ENSO's dynamics, and that WWBs should not be regarded as purely stochastic forcing. In the paradigm proposed here, WWBs are still an important aspect of ENSO's dynamics, but they are treated as being partially stochastic and partially affected by the large-scale ENSO dynamics, rather than being completely external to ENSO.It is further shown that WWB modulation by the large-scale equatorial SST field is roughly equivalent to an increase in the ocean-atmosphere coupling strength, making the coupled equatorial Pacific effectively self-sustained.

show abstract

Section: Observational Evidence Of Wwb Modulation By Ensomentioning

confidence: 85%

“…It therefore makes sense to expect that WWBs may be involved with the onset of El Niño events (Latif et al 1988; Lengaigne et al 2004;Luther et al 1983;Perigaud and Cassou 2000). Indeed, WWBs have been observed to occur in association with the onset of every significant El Niño event for the past 50 years (Kerr 1999;McPhaden 2004).…”

Section: Introductionmentioning

confidence: 99%

Westerly Wind Bursts: ENSO’s Tail Rather than the Dog?

2005

View full text Add to dashboard Cite

show abstract

“…However, because two out of these seven cases had very strong westerly winds (15ms-1 in one case and 20ms-1 in another case), this study will present results related to these two bursts. It was noted that some other westerly episodes were present in the equatorial central Pacific near 170*W during 1970-73 (e.g., Luther et al, 1983). Because the daily surface wind data in that region were not yet available to us, the present study only focuses on the short-term impact of the extratropical forcing on wind variations in the EWP and does not concentrate on the region further east.…”

Section: Data Sources and Selection Of Study Periodsmentioning

confidence: 99%

“…Over the central Pacific (*170*E to 170*W), these anomalies (i.e., not necessary to be westerly flows) are impulsive in nature and last from one to three weeks (Luther et al, 1983). These surface westerly surges generate oceanic Kelvin waves which in turn may cause the warming of the sea surface in the eastern equatorial Pacific (e.g.., Wyrtki, 1975;McCreary, 1976;Philander, 1981;Lukas et al, 1984;Harrison and Schopf, 1984;Cane and Zebiak, 1985).…”

Section: Introductionmentioning

confidence: 99%

Extratropical Forcing and the Burst of Equatorial Westerlies in the Western Pacific: A Synoptic Study

Chu

1988

Journal of the Meteorological Society of Japan

View full text Add to dashboard Cite

Based on surface winds at 6-h intervals for four Northern Winters and Springs (1970-73), two cases of strong westerly wind bursts were identified in the core of the equatorial western Pacific (*155*E). One case occurred in early April and another in early May 1972, both prior to the maximum sea surface temperature anomalies along the Peruvian coast during the 1972 ENSO event.During the Northern Spring, as an anomalously strong anticyclone moves rapidly from north-central China to its east coast, the surface wind fields to the southeast of the Philippines respond swiftly, turning from an easterly background to northerly. In the meantime, surface pressure in the far western equatorial Pacific tends to rise. These rapid equatorial resposes are probably due to gravity wave-like motions induced by the pressure-wind imbalance in the midlatitudes. The local pressure increase in the extreme western Pacific enhances the west-to-east pressure gradient in the equatorial trough zone and results in a strong westerly wind acceleration in the core of the equatorial western Pacific. This acceleration is also preceded by a west-to-east displacement of the pressure surge in the equatorial trough zone. The enhanced zonal pressure-gradient force and the associated eastward displacement of the equatorial pressure surge are two critical factors for initiating westerly wind bursts. Westerly wind surges detected primarily from fixed-station data compare favorably with those calculated from ship records of an independent source.

show abstract

“…Keen (1982) analyzed cyclone pairs developed in the equatorial western Pacific and pointed out their important role in ENSO by maintaining and expanding the warm equatorial sea surface temperature (SST) anomaly. Luther et al(1983) demonstrated that the westerly wind bursts occur intermittently leading up to the El Nino onset.…”

Section: Introductionmentioning

confidence: 99%

Development of a Twin Cyclone and Westerly Bursts during the Initial Phase of the 1986-87 El Nino

Nitta

1989

Journal of the Meteorological Society of Japan

View full text Add to dashboard Cite

Convective activity, low-level winds and sea surface temperature associated with a twin cyclone developed in tropical western Pacific during May 1986 were analyzed in connection with the initiation of the 1986-87 El Nino. The westerly bursts over the equator were greatly intensified, corresponding to the development of the twin cyclone resulting in an eastward expansion of the warm surface water toward the dateline. This event, together with other intraseasonal variations of convection, seems to provide favorable conditions for the 1986-87 El Nino onset.

show abstract

Zonal Winds in the Central Equatorial Pacific and El Niño

Cited by 150 publications

References 23 publications

Westerly Wind Bursts: ENSO’s Tail Rather than the Dog?

Westerly Wind Bursts: ENSO’s Tail Rather than the Dog?

Extratropical Forcing and the Burst of Equatorial Westerlies in the Western Pacific: A Synoptic Study

Development of a Twin Cyclone and Westerly Bursts during the Initial Phase of the 1986-87 El Nino

Contact Info

Product

Resources

About