Warm Pool and Cold Tongue El Niño Events as Simulated by the GFDL 2.1 Coupled GCM

2010 ◽  
Vol 23 (5) ◽  
pp. 1226-1239 ◽  
Author(s):  
Jong-Seong Kug ◽  
Jung Choi ◽  
Soon-Il An ◽  
Fei-Fei Jin ◽  
Andrew T. Wittenberg
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
The Other ◽  
Discharge Process ◽  
Cold Tongue ◽  
Coupled Gcm ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Recent studies report that two types of El Niño events have been observed. One is the cold tongue (CT) El Niño, which is characterized by relatively large sea surface temperature (SST) anomalies in the eastern Pacific, and the other is the warm pool (WP) El Niño, in which SST anomalies are confined to the central Pacific. Here, both types of El Niño events are analyzed in a long-term coupled GCM simulation. The present model simulates the major observed features of both types of El Niño, incorporating the distinctive patterns of each oceanic and atmospheric variable. It is also demonstrated that each type of El Niño has quite distinct dynamic processes, which control their evolutions. The CT El Niño exhibits strong equatorial heat discharge poleward and thus the dynamical feedbacks control the phase transition from a warm event to a cold event. On the other hand, the discharge process in the WP El Niño is weak because of its spatial distribution of ocean dynamic field. The positive SST anomaly of WP El Niño is thermally damped through the intensified evaporative cooling.

Two Types of El Niño Events: Cold Tongue El Niño and Warm Pool El Niño

2009 ◽  
Vol 22 (6) ◽  
pp. 1499-1515 ◽  
Author(s):  
Jong-Seong Kug ◽  
Fei-Fei Jin ◽  
Soon-Il An
Keyword(s):  
Spatial Patterns ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Discharge Process ◽  
Cold Tongue ◽  
El Niño Events ◽  
Sst Anomaly ◽  
Sst Anomalies ◽  
El Nino Events

Abstract In this study, two types of El Niño events are classified based on spatial patterns of the sea surface temperature (SST) anomaly. One is the cold tongue (CT) El Niño, which can be regarded as the conventional El Niño, and the other the warm pool (WP) El Niño. The CT El Niño is characterized by relatively large SST anomalies in the Niño-3 region (5°S–5°N, 150°–90°W), while the WP El Niño is associated with SST anomalies mostly confined to the Niño-4 region (5°S–5°N, 160°E–150°W). In addition, spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of El Niño events. Furthermore, the difference in the transition mechanism between the two types of El Niño is clearly identified. That is, the discharge process of the equatorial heat content associated with the WP El Niño is not efficient owing to the spatial structure of SST anomaly; as a result, it cannot trigger a cold event. It is also demonstrated that zonal advective feedback (i.e., zonal advection of mean SST by anomalous zonal currents) plays a crucial role in the development of a decaying SST anomaly associated with the WP El Niño, while thermocline feedback is a key process during the CT El Niño.

scholarly journals Response of the Antarctic Stratosphere to Two Types of El Niño Events

2011 ◽  
Vol 68 (4) ◽  
pp. 812-822 ◽  
Author(s):  
M. M. Hurwitz ◽  
P. A. Newman ◽  
L. D. Oman ◽  
A. M. Molod
Keyword(s):  
El Niño ◽  
Planetary Wave ◽  
El Nino ◽  
Warm Pool ◽  
Cold Tongue ◽  
Quasi Biennial Oscillation ◽  
El Niño Events ◽  
The Antarctic ◽  
Sst Anomalies ◽  
El Nino Events

Abstract This study is the first to identify a robust El Niño–Southern Oscillation (ENSO) signal in the Antarctic stratosphere. El Niño events between 1979 and 2009 are classified as either conventional “cold tongue” events (positive SST anomalies in the Niño-3 region) or “warm pool” events (positive SST anomalies in the Niño-4 region). The 40-yr ECMWF Re-Analysis (ERA-40), NCEP, and Modern Era Retrospective–Analysis for Research and Applications (MERRA) meteorological reanalyses are used to show that the Southern Hemisphere stratosphere responds differently to these two types of El Niño events. Consistent with previous studies, cold tongue events do not impact temperatures in the Antarctic stratosphere. During warm pool El Niño events, the poleward extension and increased strength of the South Pacific convergence zone favor an enhancement of planetary wave activity during September–November. On average, these conditions lead to higher polar stratospheric temperatures and a weakening of the Antarctic polar jet in November and December, as compared with neutral ENSO years. The phase of the quasi-biennial oscillation (QBO) modulates the stratospheric response to warm pool El Niño events; the strongest planetary wave driving events are coincident with the easterly phase of the QBO.

scholarly journals The Annual-Cycle Modulation of Meridional Asymmetry in ENSO’s Atmospheric Response and Its Dependence on ENSO Zonal Structure

2015 ◽  
Vol 28 (14) ◽  
pp. 5795-5812 ◽  
Author(s):  
Wenjun Zhang ◽  
Haiyan Li ◽  
Fei-Fei Jin ◽  
Malte F. Stuecker ◽  
Andrew G. Turner ◽  
...  
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Atmospheric Response ◽  
Central Pacific ◽  
Cp El Niño ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Previous studies documented that a distinct southward shift of central Pacific low-level wind anomalies occurring during the ENSO decaying phase is caused by an interaction between the western Pacific annual cycle and El Niño–Southern Oscillation (ENSO) variability. The present study finds that the meridional movement of the central Pacific wind anomalies appears only during traditional eastern Pacific El Niño (EP El Niño) events rather than in central Pacific El Niño (CP El Niño) events in which sea surface temperature (SST) anomalies are confined to the central Pacific. The zonal structure of ENSO-related SST anomalies therefore has an important effect on meridional asymmetry in the associated atmospheric response and its modulation by the annual cycle. In contrast to EP El Niño events, the SST anomalies of CP El Niño events extend farther west toward the warm pool region with its climatological warm SSTs. In the warm pool region, relatively small SST anomalies are thus able to excite convection anomalies on both sides of the equator, even with a meridionally asymmetric SST background state. Therefore, almost meridionally symmetric precipitation and wind anomalies are observed over the central Pacific during the decaying phase of CP El Niño events. The SST anomaly pattern of La Niña events is similar to CP El Niño events with a reversed sign. Accordingly, no distinct southward displacement of the atmospheric response occurs over the central Pacific during the La Niña decaying phase. These results have important implications for ENSO climate impacts over East Asia, since the anomalous low-level anticyclone over the western North Pacific is an integral part of the annual cycle–modulated ENSO response.

Different responses of Central Asian precipitation to strong and weak El Niño events

2021 ◽  
pp. 1-60
Keyword(s):  
Soil Moisture ◽  
Central Asia ◽  
El Niño ◽  
El Nino ◽  
Moisture Flux ◽  
The Arctic ◽  
Central Asian ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events

Abstract The present study investigated impacts of strong and weak El Niño events on Central Asian precipitation variability from El Niño developing years to decaying years. It is found that strong El Niño events persistently enhance Central Asian precipitation from the mature winter to decaying summer. Large warm sea surface temperature (SST) anomalies in the tropical central-eastern Pacific induce anomalous upper-level divergence and updraft over Central Asia through large-scale convergence and divergence in the mature winter and decaying spring. Meanwhile, the associated wind anomalies induce anomalous eastward and northeastward moisture flux from the North Atlantic and Arabian Sea to Central Asia. Both anomalous ascent and moisture flux convergence favor above-normal precipitation over Central Asia in the mature winter and decaying spring. The El Niño events induced Central Asian precipitation anomalies are extended to the decaying summer due to the role of soil moisture. Increased rainfall in winter and spring enhances soil moisture in the following summer, which in turn, contributes to more precipitation in summer through modulating regional evaporation. During weak El Niño events, significant wet anomalies are only seen in the developing autumn, which result from anomalous southeastward moisture flux from the Arctic Ocean, and the abnormal signals are weak in the other seasons. The different responses of Central Asian precipitation to strong and weak El Niño events may be attributed to the difference in intensity of tropical SST anomalies between the two types of events.

El Niño Modoki Impacts on Australian Rainfall

2009 ◽  
Vol 22 (11) ◽  
pp. 3167-3174 ◽  
Author(s):  
Andréa S. Taschetto ◽  
Matthew H. England
Keyword(s):  
El Niño ◽  
El Nino ◽  
Central Pacific ◽  
Maximum Rainfall ◽  
El Niño Modoki ◽  
El Niño Events ◽  
The Impact ◽  
Sst Anomalies ◽  
Australian Rainfall ◽  
El Nino Events

Abstract This study investigates interseasonal and interevent variations in the impact of El Niño on Australian rainfall using available observations from the postsatellite era. Of particular interest is the difference in impact between classical El Niño events wherein peak sea surface temperature (SST) anomalies appear in the eastern Pacific and the recently termed El Niño “Modoki” events that are characterized by distinct warm SST anomalies in the central Pacific and weaker cold anomalies in the west and east of the basin. A clear interseasonal and interevent difference is apparent, with the maximum rainfall response for Modoki events occurring in austral autumn compared to austral spring for classical El Niños. Most interestingly, the Modoki and non-Modoki El Niño events exhibit a marked difference in rainfall impact over Australia: while classical El Niños are associated with a significant reduction in rainfall over northeastern and southeastern Australia, Modoki events appear to drive a large-scale decrease in rainfall over northwestern and northern Australia. In addition, rainfall variations during March–April–May are more sensitive to the Modoki SST anomaly pattern than the conventional El Niño anomalies to the east.

Indian Ocean Variability in the GFDL Coupled Climate Model

2007 ◽  
Vol 20 (13) ◽  
pp. 2895-2916 ◽  
Author(s):  
Qian Song ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Deep Convection ◽  
Warm Pool ◽  
Surface Winds ◽  
Pacific Warm Pool ◽  
El Niño Events ◽  
The Indian Ocean ◽  
El Nino Events

Abstract The interannual variability of the Indian Ocean, with particular focus on the Indian Ocean dipole/zonal mode (IODZM), is investigated in a 250-yr simulation of the GFDL coupled global general circulation model (CGCM). The CGCM successfully reproduces many fundamental characteristics of the climate system of the Indian Ocean. The character of the IODZM is explored, as are relationships between positive IODZM and El Niño events, through a composite analysis. The IODZM events in the CGCM grow through feedbacks between heat-content anomalies and SST-related atmospheric anomalies, particularly in the eastern tropical Indian Ocean. The composite IODZM events that co-occur with El Niño have stronger anomalies and a sharper east–west SSTA contrast than those that occur without El Niño. IODZM events, whether or not they occur with El Niño, are preceded by distinctive Indo-Pacific warm pool anomaly patterns in boreal spring: in the central Indian Ocean easterly surface winds, and in the western equatorial Pacific an eastward shift of deep convection, westerly surface winds, and warm sea surface temperature. However, delayed onsets of the anomaly patterns (e.g., boreal summer) are often not followed by IODZM events. The same anomaly patterns often precede El Niño, suggesting that the warm pool conditions favorable for both IODZM and El Niño are similar. Given that IODZM events can occur without El Niño, it is proposed that the observed IODZM–El Niño relation arises because the IODZM and El Niño are both large-scale phenomena in which variations of the Indo-Pacific warm pool deep convection plays a central role. Yet each phenomenon has its own dynamics and life cycle, allowing each to develop without the other. The CGCM integration also shows substantial decadal modulation of the occurrence of IODZM events, which is found to be not in phase with that of El Niño events. There is a weak, though significant, negative correlation between the two. Moreover, the statistical relationship between the IODZM and El Niño displays strong decadal variability.

scholarly journals On the role of the south Pacific subtropical high at the onset of El Niño events

2018 ◽  
Author(s):  
Youjia Zou ◽  
Xiangying Xi
Keyword(s):  
El Niño ◽  
El Nino ◽  
South Pacific ◽  
Warm Pool ◽  
Equatorial Pacific ◽  
Subtropical High ◽  
Trade Winds ◽  
Southward Shift ◽  
El Niño Events ◽  
El Nino Events

Abstract. Previous studies have suggested that an eastward propagation of the warm pool in the western Pacific during El Niño events may be induced by a weakening of the easterly Trade Winds (Alexander et al., 2002; Bjerknes, 1969). However, the dynamic mechanism of the Trade Winds weakening is not well understood. Here we use a model and other published proxy records to demonstrate that the anomalous southward shift of the south Pacific subtropical high (SPSH) may play a crucial role at the onset of El Niño events. By analyzing the relationship between the Trade Winds, the Equatorial Currents, the Eastern Boundary Currents and the SPSH, we find that an anomalous southward shift of the SPSH can result in a weakening of the SE Trade Winds and a southward intrusion of the NE Trade Winds, leading to a southward migration of the Trade Wind-induced Equatorial Currents, including the Equatorial Countercurrent (from ~5°–8° N to ~0°). The warm pool in the western equatorial Pacific is therefore forced to propagate eastward by the enhanced Equatorial Countercurrent and, thus, a warm phase in the central or the eastern equatorial Pacific. Moreover, the equatorward upwelling in the eastern South Pacific, usually recurving along the equator, shifts southward along with the SPSH, in turn diverts towards the west at ~15° S to feed the westward South Equatorial Currents, resulting in a failure of cooling sea surface in the eastern tropical Pacific, thus a flattening of the thermocline. The model experiments indicate that the meridional position and intensity of the Equatorial Countercurrent in the Pacific are some of the determining factors in giving rise to El Niño diversity, suggesting that there should be more frequent warm events due to a meridional expansion of the warm pool under global warming.

scholarly journals Maximizing ENSO as a source of western US hydroclimate predictability

2019 ◽  
Vol 54 (1-2) ◽  
pp. 351-372 ◽  
Author(s):  
Christina M. Patricola ◽  
John P. O’Brien ◽  
Mark D. Risser ◽  
Alan M. Rhoades ◽  
Travis A. O’Brien ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Global Climate Model ◽  
Western Us ◽  
El Niño Events ◽  
Fixed Region ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Until recently, the El Niño–Southern Oscillation (ENSO) was considered a reliable source of winter precipitation predictability in the western US, with a historically strong link between extreme El Niño events and extremely wet seasons. However, the 2015–2016 El Niño challenged our understanding of the ENSO-precipitation relationship. California precipitation was near-average during the 2015–2016 El Niño, which was characterized by warm sea surface temperature (SST) anomalies of similar magnitude compared to the extreme 1997–1998 and 1982–1983 El Niño events. We demonstrate that this precipitation response can be explained by El Niño’s spatial pattern, rather than internal atmospheric variability. In addition, observations and large-ensembles of regional and global climate model simulations indicate that extremes in seasonal and daily precipitation during strong El Niño events are better explained using the ENSO Longitude Index (ELI), which captures the diversity of ENSO’s spatial patterns in a single metric, compared to the traditional Niño3.4 index, which measures SST anomalies in a fixed region and therefore fails to capture ENSO diversity. The physically-based ELI better explains western US precipitation variability because it tracks the zonal shifts in tropical Pacific deep convection that drive teleconnections through the response in the extratropical wave-train, integrated vapor transport, and atmospheric rivers. This research provides evidence that ELI improves the value of ENSO as a predictor of California’s seasonal hydroclimate extremes compared to traditional ENSO indices, especially during strong El Niño events.

The Late Fall Extratropical Response to ENSO: Sensitivity to Coupling and Convection in the Tropical West Pacific

2008 ◽  
Vol 21 (23) ◽  
pp. 6101-6118 ◽  
Author(s):  
Ileana Bladé ◽  
Matthew Newman ◽  
Michael A. Alexander ◽  
James D. Scott
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Surface Cooling ◽  
West Pacific ◽  
The North ◽  
Late Fall ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events

Abstract The extratropical response to El Niño in late fall departs considerably from the canonical El Niño signal. Observational analysis suggests that this response is modulated by anomalous forcing in the tropical west Pacific (TWP), so that a strong fall El Niño teleconnection is more likely when warm SST conditions and/or enhanced convection prevail in the TWP. While these TWP SST anomalies may arise from noise and/or long-term variability, they may also be generated by differences between El Niño events, through variations in the tropical “atmospheric bridge.” This bridge typically drives subsidence west of the date line and enhanced trade winds over the far TWP, which cool the ocean. In late fall, however, some relatively weaker and/or more eastward-shifted El Niño events produce a correspondingly weakened and displaced tropical bridge, which results in no surface cooling and enhanced convection in the TWP. Because the North Pacific circulation is very sensitive to forcing from the TWP at this time of year, the final outcome is a strong extratropical El Niño teleconnection. This hypothesis is partly supported by regionally coupled ensemble GCM simulations for the 1950–99 period, in which prescribed observed El Niño SST anomalies in the eastern/central equatorial Pacific and an oceanic mixed layer model elsewhere coexist, so that the TWP is allowed to interact with the El Niño atmospheric bridge. To separate the deterministic signal driven by TWP coupling from that associated with inter–El Niño differences and from the “noise” due to intrinsic TWP convection variability (not induced by local SST anomalies), a second large-ensemble (100) simulation of the 1997/98 El Niño event, with coupling limited to the TWP and tropical Indian Ocean, is carried out. Together, the model findings suggest that the extratropical El Niño teleconnection during late fall is very sensitive to convective forcing in the TWP and that coupling-induced warming in the TWP may enhance this El Niño teleconnection by promoting convection in this critical TWP region. A more general implication is that diagnostic studies using December–February (DJF) seasonal averages may obscure some important aspects of climate anomalies associated with forcing in the tropical Pacific.

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