scholarly journals Interactive Feedback between ENSO and the Indian Ocean

2006 ◽  
Vol 19 (9) ◽  
pp. 1784-1801 ◽  
Author(s):  
Jong-Seong Kug ◽  
In-Sik Kang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Western Pacific ◽  
Easterly Wind ◽  
Mature Phase ◽  
La Nina ◽  
The Indian Ocean ◽  
The Western Pacific

Abstract A feedback process of the Indian Ocean SST on ENSO is investigated by using observed data and atmospheric GCM. It is suggested that warming in the Indian Ocean produces an easterly wind stress anomaly over Indonesia and the western edge of the Pacific during the mature phase of El Niño. The anomalous easterly wind in the western Pacific during El Niño helps a rapid termination of El Niño and a fast transition to La Niña by generating upwelling Kelvin waves. Thus, warming in the Indian Ocean, which is a part of the El Niño signal, operates as a negative feedback mechanism to ENSO. This Indian Ocean feedback appears to operate mostly for relatively strong El Niños and results in a La Niña one year after the mature phase of the El Niño. This 1-yr period of phase transition implies a possible role of Indian Ocean–ENSO coupling in the biennial tendency of the ENSO. Atmospheric GCM experiments show that Indian Ocean SST forcing is mostly responsible for the easterly wind anomalies in the western Pacific.

The Influence of the Indian Ocean on ENSO Stability and Flavor

2017 ◽  
Vol 30 (7) ◽  
pp. 2601-2620 ◽  
Author(s):  
Claudia E. Wieners ◽  
Henk A. Dijkstra ◽  
Will P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
Spatial Pattern ◽  
El Niño ◽  
East Coast ◽  
El Nino ◽  
La Niña ◽  
Enso Cycle ◽  
Central Pacific ◽  
La Nina ◽  
The Indian Ocean

The effect of long-term trends and interannual, ENSO-driven variability in the Indian Ocean (IO) on the stability and spatial pattern of ENSO is investigated with an intermediate-complexity two-basin model. The Pacific basin is modeled using a fully coupled (i.e., generating its own background state) Zebiak–Cane model. IO sea surface temperature (SST) is represented by a basinwide warming pattern whose strength is constant or varies at a prescribed lag to ENSO. Both basins are coupled through an atmosphere transferring information between them. For the covarying IO SST, a warm IO during the peak of El Niño (La Niña) dampens (destabilizes) ENSO, and a warm IO during the transition from El Niño to La Niña (La Niña to El Niño) shortens (lengthens) the period. The influence of the IO on the spatial pattern of ENSO is small. For constant IO warming, the ENSO cycle is destabilized because stronger easterlies induce more background upwelling, more thermocline steepening, and a stronger Bjerknes feedback. The SST signal at the east coast weakens or reverses sign with respect to the main ENSO signal [i.e., ENSO resembles central Pacific (CP) El Niños]. This is due to a reduced sensitivity of the SST to thermocline variations in case of a shallow background thermocline, as found near the east coast for a warm IO. With these results, the recent increase in CP El Niño can possibly be explained by the substantial IO (and west Pacific) warming over the last decades.

scholarly journals The Seasonal Development of an SST Anomaly in the Indian Ocean and Its Relationship to ENSO

2007 ◽  
Vol 20 (1) ◽  
pp. 38-52 ◽  
Author(s):  
Motoki Nagura ◽  
Masanori Konda
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
La Niña ◽  
Seasonal Development ◽  
La Nina ◽  
The Indian Ocean ◽  
Dipole Pattern ◽  
Sst Anomaly

Abstract The seasonal development of the sea surface temperature (SST) anomaly in the Indian Ocean is investigated in relation to El Niño–Southern Oscillation (ENSO), using NOAA optimally interpolated SST and NCEP reanalysis data. The result shows that the onset season of El Niño affects the seasonal development of surface wind anomalies over the equatorial eastern Indian Ocean (EEIO); these surface wind anomalies, in turn, determine whether the SST anomaly in the EEIO evolves into the eastern pole of the dipole pattern. In years when the dipole pattern develops, surface zonal wind anomalies over the EEIO switch from westerly to easterly in spring as La Niña switches to El Niño. The seasonal zonal wind over the EEIO also switches from westerly to easterly in spring, and the anomalous wind strengthens seasonal wind from winter to summer. Stronger winds and resultant thermal forcings produce the negative SST anomaly in the EEIO in winter, and its amplitude increases in summer. The SST anomaly becomes the eastern pole of the dipole pattern in fall. In contrast, if the change from La Niña to El Niño is delayed until late summer/fall or if La Niña persists throughout the year, a westerly anomaly persists from winter to summer over the EEIO. The persistent westerly anomaly strengthens the wintertime climatological westerlies and weakens the summertime easterlies. Therefore, negative SST anomalies are produced in the EEIO in winter, but the amplitude decreases in summer, and the eastern pole is not present in fall. The above explanation also applies to onset years of La Niña if the signs of the anomalies are reversed.

scholarly journals Representation of MJO Variability in the NCEP Climate Forecast System

2011 ◽  
Vol 24 (17) ◽  
pp. 4676-4694 ◽  
Author(s):  
Scott J. Weaver ◽  
Wanqiu Wang ◽  
Mingyue Chen ◽  
Arun Kumar
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
La Nina ◽  
The Indian Ocean ◽  
Ncep Climate Forecast System

The Madden–Julian oscillation (MJO) is arguably the most important intraseasonal mode of climate variability, given its significant modulation of global climate variations and attendant societal impacts. Advancing the current understanding and simulation of the MJO using state-of-the-art climate data and modeling systems is thus a necessary goal for improving MJO prediction capability. MJO variability is assessed in NOAA/NCEP reanalyses and two versions of the Climate Forecast System (CFS), CFS version 1 (CFSv1) and its update version 2 (CFSv2). The analysis leans on a variety of diagnostic procedures and includes MJO sensitivity to varying El Niño–Southern Oscillation (ENSO) phases. It is found that significant improvements have been realized in the representation of MJO variations in the new NCEP Climate Forecast System reanalysis (CFSR) as evidenced by outgoing longwave radiation (OLR) power spectral analysis and more coherent propagation characteristics of precipitation and 850-hPa zonal winds over the Eastern Hemisphere in CFSR-only depictions. Conversely, while modest improvements are realized in the CFSv2 as compared to CFSv1, in general the simulation of the MJO continues to be a challenge. Both versions produce strong eastward propagating variance of convection and wind fields in the intraseasonal frequency band. However, the simulated MJO propagates slower than the observed with difficulties traversing the Maritime Continent into the western Pacific, as noted in many previous modeling studies. The CFS shows robust intraseasonal simulations over the west Pacific during El Niño years with diminished simulation capability over the Indian Ocean during La Niña years. This is likely a manifestation of the preference for La Niña MJO activity to occur over the Indian Ocean and the simulation challenges over that domain.

scholarly journals Biophysical responses near equatorial islands in the Western Pacific Ocean during El Niño/La Niña transitions

2013 ◽  
Vol 40 (20) ◽  
pp. 5473-5479 ◽  
Author(s):  
Michelle M. Gierach ◽  
Monique Messié ◽  
Tong Lee ◽  
Kristopher B. Karnauskas ◽  
Marie-Hélène Radenac
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Western Pacific ◽  
Western Pacific Ocean ◽  
La Nina ◽  
The Western Pacific

The Influence of Atmospheric Convection on the Interaction between the Indian Ocean and ENSO

2017 ◽  
Vol 30 (24) ◽  
pp. 10155-10178 ◽  
Author(s):  
Claudia E. Wieners ◽  
Henk A. Dijkstra ◽  
Will P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Western Pacific ◽  
Water Volume ◽  
Maritime Continent ◽  
Enso Events ◽  
The Indian Ocean ◽  
The Western Pacific

In recent years it has been proposed that a negative (positive) Indian Ocean dipole (IOD) in boreal autumn favors an El Niño (La Niña) at a lead time of 15 months. Observational analysis suggests that a negative IOD might be accompanied by easterly anomalies over the western Pacific. Such easterlies can enhance the western Pacific warm water volume, thus favoring El Niño development from the following boreal spring onward. However, a Gill-model response to a negative IOD forcing would lead to nearly zero winds over the western Pacific. The authors hypothesize that a negative IOD—or even a cool western Indian Ocean alone—leads to low-level air convergence and hence enhanced convectional heating over the Maritime Continent, which in turn amplifies the wind convergence so as to cause easterly winds over the western Pacific. This hypothesis is tested by coupling an idealized Indian Ocean model and a convective feedback model over the Maritime Continent to the Zebiak–Cane model. It is found that, for a sufficiently strong convection feedback, a negative (positive) IOD indeed forces easterlies (westerlies) over the western Pacific. The contribution from the eastern IOD pole dominates. IOD variability is found to destabilize the El Niño–Southern Oscillation (ENSO) mode, whereas Indian Ocean basinwide warming (IOB) variability dampens ENSO, even in the presence of convection. The influence of the Indian Ocean on the spectral properties of ENSO is dominated by the IOB, while the IOD is a better predictor for individual ENSO events.

scholarly journals Links between Tropical Pacific SST and Cholera Incidence in Bangladesh: Role of the Western Tropical and Central Extratropical Pacific

2009 ◽  
Vol 22 (7) ◽  
pp. 1641-1660 ◽  
Author(s):  
Benjamin A. Cash ◽  
Xavier Rodó ◽  
James L. Kinter
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Monsoon Circulation ◽  
Global Response ◽  
The Indian Ocean ◽  
The Western Pacific ◽  
Sst Anomalies

Abstract Recent studies arising from both statistical analysis and dynamical disease models demonstrate a link between the incidence of cholera, a paradigmatic waterborne bacterial illness endemic to Bangladesh, and the El Niño–Southern Oscillation (ENSO). The physical significance of this relationship was investigated by examining links between the regional climate of Bangladesh and western Pacific sea surface temperatures (SST) associated with ENSO using a pacemaker configuration of the Center for Ocean–Land–Atmosphere Studies atmospheric general circulation model. The global SST response to ENSO SST anomalies in the western Pacific alone is found to be relatively weak and unrealistic when compared to observations, indicating that the global response to ENSO is driven primarily by anomalies in the central and eastern tropical Pacific. Despite the weak global response to western Pacific SST anomalies, however, a signal is found in summer rainfall over India and Bangladesh. Specifically, reduced rainfall typically follows winter El Niño events. In the absence of warm SST anomalies in the eastern Pacific, cold anomalies in the western Pacific produce a La Niña–like response in the model circulation. Cold SST anomalies suppress convection over the western Pacific. Large-scale convergence shifts into the eastern Indian Ocean and modifies the summer monsoon circulation over India and Bangladesh. The probabilistic relationship between Bangladesh rainfall and SST is also explored using a nonparametric statistical technique. Decreased rainfall is strongly associated with cold SST in the western Pacific, while associations between SST and enhanced rainfall are substantially weaker. Also found are strong associations between rainfall and SST in the Indian Ocean in the absence of differences in forcing from the western Pacific. It thus appears that the Indian Ocean may represent an independent source of predictability for the monsoon and cholera risk. Likewise, under certain circumstances, the western Pacific may also exert a significant influence on Bangladesh rainfall and cholera risk.

scholarly journals Interactive Feedback between ENSO and the Indian Ocean in an Interactive Ensemble Coupled Model

2006 ◽  
Vol 19 (24) ◽  
pp. 6371-6381 ◽  
Author(s):  
Jong-Seong Kug ◽  
Ben P. Kirtman ◽  
In-Sik Kang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Coupled Model ◽  
Walker Circulation ◽  
Western Pacific ◽  
The Indian Ocean ◽  
Oceanic Upwelling ◽  
Interactive Feedback ◽  
The Western Pacific

Abstract An interactive feedback between ENSO and the Indian Ocean is investigated using a Center for Ocean–Land–Atmosphere Studies (COLA) interactive ensemble coupled model. From a long-term simulation of the coupled GCM, it is shown that El Niño events terminate relatively rapidly when the Indian Ocean SST is anomalously warm. The anomalous Indian Ocean warming induces the anomalous easterlies over the western Pacific by modulating the Walker circulation. In turn, the anomalous easterlies generate oceanic-upwelling Kelvin waves over the western Pacific, which propagate eastward and accelerate the decay of the warm SST in the eastern Pacific. As a result, El Niño terminates relatively quickly, and the phase transition from El Niño to La Niña progresses rapidly. These interactive processes are consistent with those derived from the previous observational analyses.

scholarly journals Differences in the Reaction of North Equatorial Countercurrent to the Developing and Mature Phase of ENSO Events in the Western Pacific Ocean

Climate ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 57
Author(s):  
Yusuf Jati Wijaya ◽  
Yukiharu Hisaki
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Enso Event ◽  
Western Pacific ◽  
Western Pacific Ocean ◽  
Mature Phase ◽  
La Nina ◽  
La Nina Event ◽  
The Western Pacific

The North Equatorial Countercurrent (NECC) is an eastward zonal current closely related to an El Niño Southern Oscillation (ENSO) event. This paper investigated the variations of NECC in the Western Pacific Ocean over 25 years (1993–2017) using satellite data provided by the Copernicus Marine Environment Monitoring Service (CMEMS) and the Remote Sensing System (RSS). The first mode of empirical orthogonal function (EOF) analysis showed that the NECC strengthened or weakened in each El Niño (La Niña) event during the developing or mature phase, respectively. We also found that the NECC shifting was strongly coincidental with an ENSO event. During the developing phase of an El Niño (La Niña) event, the NECC shifted southward (northward), and afterward, when it entered the mature phase, the NECC tended to shift slightly northward (southward). Moreover, the NECC strength was found to have undergone a weakening during the 2008–2017 period.

scholarly journals The unique mean seasonal cycle in the Indian Ocean anchors its various air-sea coupled modes across the basin

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Xinqiang Xu ◽  
Lei Wang ◽  
Weidong Yu
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
La Niña ◽  
Trade Wind ◽  
Coupled Modes ◽  
La Nina ◽  
The Indian Ocean

AbstractThe interannual variability of the sea surface temperature (SST) in the Indian Ocean is complex and characterized by various air-sea coupled modes, which occur around El Niño/La Niña's peak phase (i.e. December–January–February, DJF). Indian Ocean Dipole Mode (IODM) develops over the tropical Indian Ocean and peaks in September–October–November (SON), while Ningaloo Niño, Subtropical Indian Ocean Dipole (SIOD) and Indian Ocean Basin Mode (IOBM) occur respectively over northwest off Australia, subtropical and tropical Indian Ocean, during boreal winter to spring. The apparent contrast between their divergent regionality and convergent seasonality around DJF triggers the present study to examine the interaction between the local mean monsoonal cycle and the anomalous forcing from El Niño/La Niña. The diagnosis confirms that the Indian Ocean’s unique complexity, including the monsoonal circulation over the tropics and the trade wind over the subtropical southern Indian Ocean, plays the fundamental role in anchoring the various regional air-sea coupled modes across the basin. The SST anomalies can be readily explained by the wind-evaporation-SST (WES) mechanism, which works together with other more regional-dependent dynamic and thermodynamic mechanisms. This implies that El Niño/La Niña brings much predictability for the Indian Ocean variations.

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