scholarly journals Weakened Interannual Variability in the Tropical Pacific Ocean since 2000

2013 ◽  
Vol 26 (8) ◽  
pp. 2601-2613 ◽  
Author(s):  
Zeng-Zhen Hu ◽  
Arun Kumar ◽  
Hong-Li Ren ◽  
Hui Wang ◽  
Michelle L’Heureux ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Interannual Variability ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Tropical Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Tropical Pacific Ocean ◽  
Trade Winds ◽  
The Tropical Pacific

Abstract An interdecadal shift in the variability and mean state of the tropical Pacific Ocean is investigated within the context of changes in El Niño–Southern Oscillation (ENSO). Compared with 1979–99, the interannual variability in the tropical Pacific was significantly weaker in 2000–11, and this shift can be seen by coherent changes in both the tropical atmosphere and ocean. For example, the equatorial thermocline tilt became steeper during 2000–11, which was consistent with positive (negative) sea surface temperature anomalies, increased (decreased) precipitation, and enhanced (suppressed) convection in the western (central and eastern) tropical Pacific, which reflected an intensification of the Walker circulation. The combination of a steeper thermocline slope with stronger surface trade winds is proposed to have hampered the eastward migration of the warm water along the equatorial Pacific. As a consequence, the variability of the warm water volume was reduced and thus ENSO amplitude also decreased. Sensitivity experiments with the Zebiak–Cane model confirm the link between thermocline slope, wind stress, and the amplitude of ENSO.

scholarly journals El Niño in a changing climate: a multi-model study

Ocean Science ◽  
2005 ◽  
Vol 1 (2) ◽  
pp. 81-95 ◽  
Author(s):  
G. J. van Oldenborgh ◽  
S. Y. Philip ◽  
M Collins
Keyword(s):  
Standard Deviation ◽  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Enso Cycle ◽  
Tropical Pacific Ocean ◽  
Enso Variability ◽  
The Tropical Pacific

Abstract. In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Niño - Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability. Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally. Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Niño-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations. Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Niño and La Niña events. Based on this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.

The Climate of the Central Arizona and Phoenix Long-Term Ecological Research Site (CAP LTER) and Links to ENSO

2003 ◽  
Author(s):  
Anthony J. Brazel ◽  
Andrew W. Ellis
Keyword(s):  
United States ◽  
Pacific Ocean ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Tropical Pacific Ocean ◽  
Southwestern United States ◽  
Central Arizona ◽  
Insight Into ◽  
The Tropical Pacific

The Central Arizona and Phoenix LTER (CAP LTER) is one of two urban LTERs in the world network (Grimm et al. 2000; see http://caplter.asu.edu). Many LTER sites display a detectable climatic signal related to the El Niño–Southern Oscillation (ENSO) phenomenon (Greenland 1999). The purpose of this chapter is twofold: (1) to provide some insight into the role of the tropical Pacific Ocean as a driver of several climatic (and thus, ecologically related) variables in the CAP LTER location of central Arizona, and (2) to suggest the linkages of ENSO events to selected ecosystem processes near and within the geographical region of CAP LTER (figure 7.1a). From past studies, it is clear that the seasonal and annual climate regimes of the southwestern United States, particularly water-related parameters, are linked to the periodicities and anomalies of what is known as the Multivariate ENSO Index (MEI) and Southern Oscillation Index (SOI) (e.g., Wolter 1987; Molles and Dahm 1990; Redmond and Koch 1991; Woolhiser and Keefer 1993; Wolter and Timlin 1993; Cayan and Redmond 1994; Redmond and Cayan 1994; Cayan et al. 1999; Redmond and Cayan 1999; Simpson and Colodner 1999; Redmond 2000; and Mason and Goddard 2001). In Arizona, and especially in the CAP LTER region, precipitation is bimodal during the year with peaks in winter (mostly midlatitudederived frontal storms) and in mid-to-late summer, mostly in the form of convective thunderstorms during the North American monsoon season. Recent studies show a strong connection between ENSO and winter moisture in Arizona, such that it is even possible to forecast impending conditions in advance (Pagano et al. 1999). These studies have established relationships between the climate of the southwest ern United States and ENSO by demonstrating monthly and daily timescale effects on inputs of moisture and resultant streamflow in Arizona (e.g., Molles and Dahm 1990; Cayan et al. 1999; and Simpson and Colodner 1999). The synoptic- and largescale circulation patterns associated with anomalies of MEI/SOI in the southwestern United States provide additional insight into regional forces that drive the CAPLTER climate (e.g., Redmond and Koch 1991). Generally, when the warm phase of the tropical Pacific Ocean occurs (El Niño, thus negative SOI, positive MEI), across the Southwest precipitation is generally anomalously high.

scholarly journals El Niño in a changing climate: a multi-model study

2005 ◽  
Vol 2 (3) ◽  
pp. 267-298 ◽  
Author(s):  
G. J. van Oldenborgh ◽  
S. Philip ◽  
M. Collins
Keyword(s):  
Standard Deviation ◽  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Enso Cycle ◽  
Tropical Pacific Ocean ◽  
Enso Variability ◽  
The Tropical Pacific

Abstract. In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Niño - Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability. Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally. Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Niño-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations. Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Niño and La Niña events. Based in this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.

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