A Model Study of Oceanic Mechanisms Affecting Equatorial Pacific Sea Surface Temperature during the 1997–98 El Niño

Ocean salinity variability provides a new way to study the evolution of the the El Niño-Southern Oscillation (ENSO). Comparisons between the salinity variation and related processes responsible for sea surface temperature anomaly (SSTA) were extensively examined for the two strong El Niño (EN) events in 1997/1998 and 2015/2016, and a special EN event in 2014/2015. The results show that the development of EN is significantly correlated with a sea surface salinity anomaly (SSSA) in the tropical western-central Pacific. In the spring of 1997 and 2015 with strong EN events, the western-central equatorial Pacific exhibited significant negative SSSA that propagated eastward to the west of the dateline. The negative SSSA induced increased barrier layer thickness (BLT) which enhanced sea surface temperature (SST) warming in the tropical central Pacific. In contrast, although a negative SSSA occurred during April of the 2014/2015 weak EN event in the western-central equatorial Pacific, this SSSA was mainly confined to between 160° E and 180° E without significant eastward movement, resulting in a weakened BLT thickening process and a weak modulation effect on SST. We also confirm that the surface forcing associated with fresh water flux (FWF: evaporation (E) minus precipitation (P)) plays a prominent role in the surface salinity tendency in the tropical Pacific during EN events. Moreover, the negative FWF anomaly leads a strong negative SSSA by two months. Compared with the two strong ENs, the early negative FWF anomaly in the weak 2014/2015 EN did not present distinct development and eastward propagation and weakened rapidly in the summer of 2015. We demonstrate that change in salinity can modulate the ENSO, and the variation of SSSA and associated physical processes in the tropical western-central Pacific and could be used as an indicator for predicting the development of ENSO.

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Indian Ocean Sea Surface Temperature and El Niño–Southern Oscillation: A New Perspective

Journal of Climate ◽

10.1175/jcli3338.1 ◽

2005 ◽

Vol 18 (9) ◽

pp. 1351-1368 ◽

Cited By ~ 75

Author(s):

Pascal Terray ◽

Sébastien Dominiak

Keyword(s):

Indian Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

El Niño ◽

Regime Shift ◽

El Nino ◽

Equatorial Pacific ◽

Sea Surface ◽

Southern Indian Ocean ◽

Boreal Winter

Abstract Here the 1976–77 climate regime shift that was accompanied by a remarkable change in the lead–lag relationships between Indian Ocean sea surface temperature (SST) and El Niño evolution is shown. After the 1976–77 regime shift, a correlation analysis suggests that southern Indian Ocean SSTs observed during late boreal winter are a key precursor in predicting El Niño evolution as the traditional oceanic heat content anomalies in the equatorial Pacific or zonal wind anomalies over the equatorial western Pacific. The possible physical mechanisms underlying this highly significant statistical relationship are discussed. After the 1976–77 regime shift, southern Indian Ocean SST anomalies produced by Mascarene high pulses during boreal winter trigger coupled air–sea processes in the tropical eastern Indian Ocean during the following seasons. This produces a persistent remote forcing on the Pacific climate system, promoting wind anomalies over the western equatorial Pacific and modulating the regional Hadley cell in the southwest Pacific. These modulations, in turn, excite Rossby waves, which produce quasi-stationary circulation anomalies in the extratropical South Pacific, responsible for the development of the southern branch of the “horseshoe” El Niño pattern. The change of the background SST state that occurred in the late 1970s over the Indian Ocean may also explain why ENSO evolution is different before and after the 1976–77 regime shift. These results shed some light on the possible influence of global warming or decadal fluctuations on El Niño evolution through changes in teleconnection patterns between the Indian and Pacific Oceans.

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El Niño and La Niña-equatorial Pacific thermocline depth and sea surface temperature anomalies, 1986-98

Geophysical Research Letters ◽

10.1029/1999gl011307 ◽

2001 ◽

Vol 28 (6) ◽

pp. 1051-1054 ◽

Cited By ~ 30

Author(s):

D. E. Harrison ◽

Gabriel A. Vecchi

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

El Niño ◽

El Nino ◽

Equatorial Pacific ◽

Sea Surface ◽

Thermocline Depth ◽

Temperature Anomalies ◽

La Nina ◽

Sea Surface Temperature Anomalies

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The Influence of El Niño on the Spring Fallout of Asian Bird Species at Attu Island

Earth Interactions ◽

10.1175/2009ei272.1 ◽

2009 ◽

Vol 13 (7) ◽

pp. 1-22 ◽

Cited By ~ 4

Author(s):

Sultan Hameed ◽

Henry H. Norwood ◽

Michael Flanagan ◽

Steven Feldstein ◽

Chien-hsiung Yang

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

El Niño ◽

El Nino ◽

Equatorial Pacific ◽

Climate Impacts ◽

Sea Surface ◽

Northwest Pacific ◽

Enso Cycle ◽

Strong Impact

Abstract Several studies have documented the effect of the recent secular climate warming on the distributions and geographical ranges of birds. Here the authors report the strong impact of a recurring climatic pattern in the equatorial Pacific, the El Niño–Southern Oscillation (ENSO) cycle of warm (El Niño) and cold (La Niña) events, on spring migrants along the Far Eastern flyway in northeast Asia. In El Niño years, an unusually large number of birds that use the flyway are observed at Attu Island, westernmost of the Aleutian Islands, nearly 960 km away from the Asian coast. This study is based on a 20-yr dataset documenting the year-to-year variation of Asian birds arriving on Attu in the spring season and uses a three-phased analytical methodology to examine climate impacts on bird movements and populations. The authors offer evidence that birds are displaced toward the Attu area in strong eastward-moving storms. They also present results from a reverse trajectory model that was used to simulate trajectories that a sample of Attu arrivals likely followed in reaching the island. In a statistical analysis, it is shown that 79% of the variation of the Asian birds is explained by a single climate variable: sea surface temperature in the eastern equatorial Pacific in the previous fall. It is the rise in sea surface temperature in this region, more than 8000 km from Attu, that characterizes the onset of an El Niño episode. Examining those years for which there was a strong ENSO signal in the fall, it is found that the following May is characterized by anomalously strong westerly winds in the northwest Pacific, conditions that are appropriate for large Asian bird fallouts at Attu. Because of the time lag between the fall sea surface temperatures in the El Niño region and the spring Asian bird count at Attu, and the strong correlation between these two quantities, the number of Asian birds arriving at Attu in spring is predictable in the previous autumn. Such predictions are presented for several years.

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