scholarly journals Relationships between Extratropical Sea Level Pressure Variations and the Central Pacific and Eastern Pacific Types of ENSO

2011 ◽  
Vol 24 (3) ◽  
pp. 708-720 ◽  
Author(s):  
Jin-Yi Yu ◽  
Seon Tae Kim
Keyword(s):  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Nodal Point ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Sst Anomalies

Abstract This study examines the linkages between leading patterns of interannual sea level pressure (SLP) variability over the extratropical Pacific (20°–60°N) and the eastern Pacific (EP) and central Pacific (CP) types of El Niño–Southern Oscillation (ENSO). The first empirical orthogonal function (EOF) mode of the extratropical SLP anomalies represents variations of the Aleutian low, and the second EOF mode represents the North Pacific Oscillation (NPO) and is characterized by a meridional SLP anomaly dipole with a nodal point near 50°N. It is shown that a fraction of the first SLP mode can be excited by both the EP and CP types of ENSO. The SLP response to the EP type is stronger and more immediate. The tropical–extratropical teleconnection appears to act more slowly for the CP ENSO. During the decay phase of EP events, the associated extratropical SLP anomalies shift from the first SLP mode to the second SLP mode. As the second SLP mode grows, subtropical SST anomalies are induced beneath via surface heat flux anomalies. The SST anomalies persist after the peak in strength of the second SLP mode, likely because of the seasonal footprinting mechanism, and lead to the development of the CP type of ENSO. This study shows that the CP ENSO is an extratropically excited mode of tropical Pacific variability and also suggests that the decay of an EP type of ENSO can lead to the onset of a CP type of ENSO with the aid of the NPO. This extratropical linking mechanism appears to be at work during the 1972, 1982, and 1997 strong El Niño events, which were all EP events and were all followed by strong CP La Niña events after the NPO was excited in the extratropics. This study concludes that extratropical SLP variations play an important role in exciting the CP type of ENSO and in linking the transitions from the EP to CP events.

Linking a sea level pressure anomaly dipole over North America to the central Pacific El Niño

2016 ◽  
Vol 49 (4) ◽  
pp. 1321-1339 ◽  
Author(s):  
Ruiqiang Ding ◽  
Jianping Li ◽  
Yu-heng Tseng ◽  
Cheng Sun ◽  
Fei Zheng
Keyword(s):  
North America ◽  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Pressure Anomaly

Two types of El Niño and extratropical sea-level pressure variations

2016 ◽  
Vol 37 (22) ◽  
pp. 5443-5456 ◽  
Author(s):  
Wanjiao Song ◽  
Qing Dong ◽  
Cunjin Xue ◽  
Jin Sha
Keyword(s):  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Sea Level Pressure ◽  
Level Pressure

scholarly journals Atmospheric torques and Earth's rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño?

2017 ◽  
Vol 8 (4) ◽  
pp. 1009-1017 ◽  
Author(s):  
Sébastien B. Lambert ◽  
Steven L. Marcus ◽  
Olivier de Viron
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
Eastern Pacific ◽  
Earth’S Rotation ◽  
Length Of Day ◽  
Central Pacific ◽  
Earth's Rotation ◽  
Enso Events

Abstract. El Niño–Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east–west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015–2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern–central Pacific event, the 2015–2016 mountain torque was smaller than for the 1982–1983 and 1997–1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM–LOD signatures for all three extreme ENSO events. The 2015–2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Niño events.

scholarly journals Variations in the Three-Dimensional Structure of the Atmospheric Circulation with Different Flavors of El Niño

2009 ◽  
Vol 22 (11) ◽  
pp. 2978-2991 ◽  
Author(s):  
Kevin E. Trenberth ◽  
Lesley Smith
Keyword(s):  
Indian Ocean ◽  
Sea Level ◽  
Atmospheric Circulation ◽  
El Niño ◽  
El Nino ◽  
Three Dimensional ◽  
Positive Sign ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The Tropics

Abstract Two rather different flavors of El Niño are revealed when the full three-dimensional spatial structure of the temperature field and atmospheric circulation monthly mean anomalies is analyzed using the Japanese Reanalysis (JRA-25) temperatures from 1979 through 2004 for a core region of the tropics from 30°N to 30°S, with results projected globally onto various other fields. The first two empirical orthogonal functions (EOFs) both have primary relationships to El Niño–Southern Oscillation (ENSO) but feature rather different vertical and spatial structures. By construction the two patterns are orthogonal, but their signatures in sea level pressure, precipitation, outgoing longwave radiation (OLR), and tropospheric diabatic heating are quite similar. Moreover, they are significantly related, with EOF-2 leading EOF-1 by about 4–6 months, indicating that they play complementary roles in the evolution of ENSO events, and with each mode playing greater or lesser roles in different events and seasons. The dominant pattern (EOF-1) in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30°N to 30°S that increases in magnitude with height to 200 hPa, drops to zero about 100 hPa at the tropopause, and has reverse sign to 30 hPa with peak values at 70 hPa. It correlates strongly with global mean surface temperatures. EOF-2 emphasizes off-equatorial centers of action and strong Rossby wave temperature signatures that are coherent throughout the troposphere, with the strongest values in the Pacific that extend into the extratropics and a sign reversal at and above 150 hPa. Near the surface, both patterns feature boomerang-shaped opposite temperatures in the western tropical and subtropical Pacific, with similar sea level pressure patterns, but with EOF-1 more focused in equatorial regions. Both patterns are strongest during the boreal winter half-year when anomalous precipitation in the tropics and associated latent heating drive teleconnections throughout the world. For El Niño in northern winter EOF-1 has more precipitation in the eastern tropical Pacific, while EOF-2 has much drier conditions over northern Australia and the Indian Ocean. In northern summer, the main differences are in the South Pacific and Indian Ocean. Differences in teleconnections suggest great sensitivity to small changes in forcings in association with seasonal variations in the mean state.

scholarly journals A Coupled GCM Analysis of MJO Activity at the Onset of El Niño

2009 ◽  
Vol 66 (4) ◽  
pp. 966-983 ◽  
Author(s):  
A. G. Marshall ◽  
O. Alves ◽  
H. H. Hendon
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Ocean Dynamics ◽  
Western Pacific ◽  
Eastern Pacific ◽  
Kelvin Wave ◽  
Central Pacific ◽  
The Western Pacific

Abstract The ocean dynamics of the Madden–Julian oscillation (MJO) and its interaction with El Niño–Southern Oscillation (ENSO) are assessed using a flux-corrected coupled model experiment from the Australian Bureau of Meteorology. The model demonstrates the correct oceanic Kelvin wave response to the MJO-related westerly winds in the western Pacific. Although there may be a role for the MJO in influencing the strength of El Niño, its impact is difficult to separate from that of strong heat content preconditioning of ENSO. Hence, the MJO–ENSO relationship is assessed starting from a background state of low heat content anomalies in the western Pacific that are also characteristic of recent observed El Niño events. The model shows a strong relationship between ENSO and the MJO near the peak of El Niño. At this time, the sea surface temperature (SST) anomaly is largest in the central Pacific, and it is difficult to separate cause and effect. Near the onset of El Niño, however, when Pacific Ocean SST anomalies are near zero, an increase in MJO activity is associated with Kelvin wave activity and stronger subsequent ENSO warming. A significant increase in the number of MJO events, rather than the strength of individual MJO events, leads to stronger eastern Pacific warming; the MJO appears not to be responsible for the occurrence of El Niño itself, but, rather, is important for influencing its development thus. This research supports a role for downwelling oceanic Kelvin waves and subsequent deepening of the thermocline in contributing to eastern Pacific warming during the onset of El Niño.

scholarly journals Potential Impact of Preceding Aleutian Low Variation on El Niño–Southern Oscillation during the Following Winter

2020 ◽  
Vol 33 (8) ◽  
pp. 3061-3077 ◽  
Author(s):  
Shangfeng Chen ◽  
Wen Chen ◽  
Renguang Wu ◽  
Bin Yu ◽  
Hans-F. Graf
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Eastern Pacific ◽  
Synoptic Scale ◽  
Aleutian Low ◽  
Central Pacific ◽  
Sst Warming ◽  
Anomalous Cyclone

AbstractThe present study reveals a close relation between the interannual variation of Aleutian low intensity (ALI) in March and the subsequent winter El Niño–Southern Oscillation (ENSO). When March ALI is weaker (stronger) than normal, an El Niño (a La Niña)–like sea surface temperature (SST) warming (cooling) tends to appear in the equatorial central-eastern Pacific during the subsequent winter. The physical process linking March ALI to the following winter ENSO is as follows. When March ALI is below normal, a notable atmospheric dipole pattern develops over the North Pacific, with an anticyclonic anomaly over the Aleutian region and a cyclonic anomaly over the subtropical west-central Pacific. The formation of the anomalous cyclone is attributed to feedback of the synoptic-scale eddy-to-mean-flow energy flux and associated vorticity transportation. Specifically, easterly wind anomalies over the midlatitudes related to the weakened ALI are accompanied by a decrease in synoptic-scale eddy activity, which forces an anomalous cyclone to its southern flank. The accompanying westerly wind anomalies over the tropical west-central Pacific induce SST warming in the equatorial central-eastern Pacific during the following summer–autumn via triggering eastward-propagating warm Kelvin waves, which may sustain and develop into an El Niño event during the following winter via positive air–sea feedback. The relation of March ALI with the following winter ENSO is independent of the preceding tropical Pacific SST, the preceding-winter North Pacific Oscillation, and the spring Arctic Oscillation. The results of this analysis may provide an additional source for the prediction of ENSO.

scholarly journals Ocean Processes Affecting the Twenty-First-Century Shift in ENSO SST Variability

2016 ◽  
Vol 29 (19) ◽  
pp. 6861-6879 ◽  
Author(s):  
Cong Guan ◽  
Michael J. McPhaden
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
First Century ◽  
Eastern Pacific ◽  
Enso Cycle ◽  
Central Pacific ◽  
Temperature Variance ◽  
Sst Variability ◽  
Twenty First Century

Abstract Sea surface temperature (SST) variability associated with El Niño–Southern Oscillation (ENSO) slightly increased in the central Pacific Ocean but weakened significantly in the eastern Pacific at the beginning of twenty-first century relative to 1980–99. This decadal shift led to the greater prominence central Pacific (CP) El Niño events during the 2000s relative to the previous two decades, which were dominated by eastern Pacific (EP) events. To expand upon previous studies that have examined this shift in ENSO variability, temperature and temperature variance budgets are examined in the mixed layer of the Niño-3 (5°S–5°N, 150°–90°W) and Niño-4 (5°S–5°N, 160°E–150°W) regions from seven ocean model products spanning the period 1980–2010. This multimodel-product-based approach provides a robust assessment of dominant mechanisms that account for decadal changes in two key index regions. A temperature variance budget perspective on the role of thermocline feedbacks in the ENSO cycle based on recharge oscillator theory is also presented. As found in previous studies, thermocline and zonal advective feedbacks are the most important positive feedbacks for generating ENSO SST variance, and thermodynamic damping is the largest negative feedback for damping ENSO variance. Consistent with the shift toward more CP El Niños after 2000, thermocline feedbacks experienced a substantial reduction from 1980 to 1999 and into the 2000s, while zonal advective feedbacks were less affected. Negative feedbacks likewise weakened after 2000, particularly thermal damping in the Niño-3 region and the nonlinear sink of variance in both regions.

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