The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO

2010 ◽  
Vol 23 (5) ◽  
pp. 1095-1110 ◽  
Author(s):  
Soon-Il An ◽  
Yoo-Geun Ham ◽  
Jong-Seong Kug ◽  
Axel Timmermann ◽  
Jung Choi ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Western Pacific ◽  
Max Planck ◽  
Central Pacific ◽  
Enso Variability ◽  
Cycle Amplitude ◽  
State Changes ◽  
The Western Pacific ◽  
Background State ◽  
Mean State

Abstract The influence of the tropical Pacific annual-mean state on the annual-cycle amplitude and El Niño–Southern Oscillation (ENSO) variability is studied using the Max Planck Institute for Meteorology coupled general circulation model (CGCM) ECHAM5/Max Planck Institute Ocean Model (MPI-OM1). In a greenhouse warming experiment, an intensified annual cycle of sea surface temperature (SST) in the eastern tropical Pacific is associated with reduced ENSO variability, and vice versa. Analysis showed that the annual-mean states, especially the surface warming in the western Pacific and the thermocline deepening in the central Pacific, which is concurrent with the strong annual cycle, act to suppress ENSO amplitude and to intensify the annual-cycle amplitude, and vice versa. The western Pacific warming acts to reduce air–sea coupling strength and to shorten the ocean adjustment time scale, and the deepening of central Pacific thermocline acts to diminish vertical advection of the anomalous ocean temperature by the annual-mean upwelling. Consequently, ENSO activity is suppressed by the annual-mean states during the strong annual-cycle decades, and the opposite case associated with the weak annual-cycle decades is also true. Furthermore, the time integration of an intermediate ENSO model forced with different background state configurations, and a stability analysis of its linearized version, show that annual-mean background states during the weak (strong) annual-cycle decades are characterized by an enhanced (reduced) linear growth rate of ENSO or similarly large (small) variability of ENSO. However, the annual-cycle component of the background state changes cannot significantly modify ENSO variability. Using a hybrid coupled model, it is demonstrated that diagnosed annual-mean background states corresponding to a reduced (enhanced) annual cycle suppress (enhance) the development of the annual cycle of SST in the eastern equatorial Pacific, mainly through the weakening (intensifying) of zonal temperature advection of annual-mean SST by the annual-cycle zonal current. The above results support the idea that climate background state changes control both ENSO and the annual-cycle amplitude in opposing ways.

scholarly journals Changes in Independency between Two Types of El Niño Events under a Greenhouse Warming Scenario in CMIP5 Models

2015 ◽  
Vol 28 (19) ◽  
pp. 7561-7575 ◽  
Author(s):  
Yoo-Geun Ham ◽  
Yerim Jeong ◽  
Jong-Seong Kug
Keyword(s):  
Global Warming ◽  
El Niño ◽  
El Nino ◽  
Western Pacific ◽  
Cmip5 Models ◽  
Greenhouse Warming ◽  
Central Pacific ◽  
El Niño Events ◽  
The Western Pacific ◽  
El Nino Events

Abstract This study uses archives from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to investigate changes in independency between two types of El Niño events caused by greenhouse warming. In the observations, the independency between cold tongue (CT) and warm pool (WP) El Niño events is distinctively increased in recent decades. The simulated changes in independency between the two types of El Niño events according to the CMIP5 models are quite diverse, although the observed features are simulated to some extent in several climate models. It is found that the climatological change after global warming is an essential factor in determining the changes in independency between the two types of El Niño events. For example, the independency between these events is increased after global warming when the climatological precipitation is increased mainly over the equatorial central Pacific. This climatological precipitation increase extends convective response to the east, particularly for CT El Niño events, which leads to greater differences in the spatial pattern between the two types of El Niño events to increase the El Niño independency. On the contrary, in models with decreased independency between the two types of El Niño events after global warming, climatological precipitation is increased mostly over the western Pacific. This confines the atmospheric response to the western Pacific in both El Niño events; therefore, the similarity between them is increased after global warming. In addition to the changes in the climatological state after global warming, a possible connection of the changes in the El Niño independency with the historical mean state is discussed in this paper.

scholarly journals Western Pacific SST Prediction with an Intermediate El Niño Prediction Model

2005 ◽  
Vol 133 (5) ◽  
pp. 1343-1352 ◽  
Author(s):  
Jong-Seong Kug ◽  
In-Sik Kang ◽  
Jong-Ghap Jhun
Keyword(s):  
Prediction Model ◽  
El Niño ◽  
El Nino ◽  
Vertical Mixing ◽  
Western Pacific ◽  
Central Pacific ◽  
Modified Model ◽  
Sst Variability ◽  
Predictive Skill ◽  
The Western Pacific

Abstract To improve forecasting skills in the western Pacific sea surface temperature (SST), the authors utilized and modified an intermediate El Niño prediction model. The original model does not have the major SST thermodynamics for western Pacific SST variability, so it cannot simulate interannual variation in the western Pacific correctly. Therefore, the authors have introduced some modifications, such as heat flux and vertical mixing, into the dynamical model in order to capture SST thermodynamics more realistically. The modified model has better forecast skill than the original one, not only for the western Pacific but also for the eastern-central Pacific. The model has predictive skill up to 6-months lead time as judged by a correlation exceeding 0.5.

scholarly journals Evolution of the Madden–Julian Oscillation in Two Types of El Niño

2016 ◽  
Vol 29 (5) ◽  
pp. 1919-1934 ◽  
Author(s):  
Xiong Chen ◽  
Jian Ling ◽  
Chongyin Li
Keyword(s):  
El Niño ◽  
El Nino ◽  
Moisture Flux ◽  
Early Summer ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Central Pacific ◽  
Cp El Niño ◽  
Ep El Niño ◽  
The Western Pacific

Abstract Evolution characteristics of the Madden–Julian oscillation (MJO) during the eastern Pacific (EP) and central Pacific (CP) types of El Niño have been investigated. MJO activities are strengthened over the western Pacific during the predeveloping and developing phases of EP El Niño, but suppressed during the mature and decaying phases. In contrast, MJO activities do not show a clear relationship with CP El Niño before their occurrence over the western Pacific, but they increase over the central Pacific during the mature and decaying phases of CP El Niño. Lag correlation analyses further confirm that MJO activities over the western Pacific in boreal spring and early summer are closely related to EP El Niño up to 2–11 months later, but not for CP El Niño. EP El Niño tends to weaken the MJO and lead to a much shorter range of its eastward propagation. Anomalous descending motions over the Maritime Continent and western Pacific related to El Niño can suppress convection and moisture flux convergence there and weaken MJO activities over these regions during the mature phase of both types of El Niño. MJO activities over the western Pacific are much weaker in EP El Niño due to the stronger anomalous descending motions. Furthermore, the MJO propagates more continuously and farther eastward during CP El Niño because of robust moisture convergence over the central Pacific, which provides adequate moisture for the development of MJO convection.

scholarly journals Winter-to-Spring Transition in East Asia: A Planetary-Scale Perspective of the South China Spring Rain Onset

2008 ◽  
Vol 21 (13) ◽  
pp. 3081-3096 ◽  
Author(s):  
L. H. LinHo ◽  
Xianglei Huang ◽  
Ngar-Cheung Lau
Keyword(s):  
East Asia ◽  
South China ◽  
Stationary Wave ◽  
Rapid Expansion ◽  
Western Pacific ◽  
Monsoon Circulation ◽  
Jet Stream ◽  
The South ◽  
Central Pacific ◽  
The Western Pacific

Abstract Analysis of observations from 1979 to 2002 shows that the seasonal transition from winter to spring in East Asia is marked with a distinctive event—the onset of the south China spring rain (SCSR). In late February, the reduced thermal contrast between ocean and land leads to weakening of the Asian winter monsoon as well as the Siberian high and the Aleutian low. Meanwhile, convection over Australia and the western Pacific Maritime Continent is suppressed on the passage of the dry phase of a Madden–Julian oscillation (MJO). In conjunction with the seasonal march of monsoon circulation in the Indonesian–Australian sector, this MJO passage weakens the local thermally direct cell in the East Asia–Australia sector. This development is further accompanied by a series of adjustments in both the tropics and midlatitudes. These changes include attenuation of the planetary stationary wave, considerable weakening of the westerly jet stream over much of the central Pacific adjacent to Japan, and reduction of baroclinicity near the East Asian trough. The influence of concurrent local processes in midlatitudes on the SCSR onset is also important. The weakened jet stream is associated with confinement of frontal activities to the coastal regions of East Asia as well as with rapid expansion of the subtropical Pacific high from the eastern Pacific to the western Pacific. A parallel analysis using output from an experiment with a GFDL-coupled GCM shows that the above sequence of circulation changes is well simulated in that model.

scholarly journals Evolution and forcing mechanisms of ENSO over the last 300,000 years in CCSM3

2017 ◽  
Author(s):  
Zhengyao Lu ◽  
Zhengyu Liu ◽  
Guangshan Chen ◽  
Jian Guan
Keyword(s):  
Annual Cycle ◽  
Southern Oscillation ◽  
Linear Part ◽  
Ice Sheets ◽  
Nonlinear Frequency ◽  
Enso Variability ◽  
Thermocline Feedback ◽  
Acceleration Technique ◽  
Cycle Amplitude ◽  
Continental Ice Sheets

Abstract. The responses of El Niño-Southern Oscillation (ENSO) and the equatorial Pacific annual cycle to external forcing changes are studied in three 3,000-year-long NCAR-CCSM3 model simulations. The simulations represent the period from 300 thousand years before present (ka BP) to present day. The first idealized simulation is forced only with accelerated orbital variations, and the rest are conducted more realistically by further adding on the time-varying boundary conditions of greenhouse gases (GHGs) and continental ice sheets. It is found that orbital forcing dominates slow ENSO evolution, while the effects of GHGs and ice-sheet forcing tend to compensate each other. On the orbital time scales, ENSO variability and annual cycle amplitude change in-phase and both have pronounced precessional cycles (~ 21,000 years) modulated by variations of eccentricity. Orbital forced ENSO intensity is dominated linearly by the change of the coupled ocean-atmosphere instability, notably the Ekman upwelling feedback and the thermocline feedback; and is also possibly affected during ENSO intrinsic developing season by the remote (or extratropical) influences of the short-scale stochastic weather noises. The acceleration technique is found to dampen the precessional signal in ENSO intensity. In glacial-interglacial cycles, additionally, the weakening/strengthening of ENSO owning to a more concentrated/depleted GHGs level leaves little net signal as compensated by the effect coherent change of decaying/expanding ice sheets. They influence the ENSO variability through changes in annual cycle amplitude via a common nonlinear frequency entrainment mechanism while the GHGs effect might has an additional linear part.

scholarly journals Zonal SST Difference as a Potential Environmental Factor Supporting the Longevity of the Madden–Julian Oscillation

2018 ◽  
Vol 31 (18) ◽  
pp. 7549-7564 ◽  
Author(s):  
Tamaki Suematsu ◽  
Hiroaki Miura
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Low Frequency ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Central Pacific ◽  
The Indian Ocean ◽  
The Difference ◽  
The Western Pacific ◽  
Sst Gradient

An environment favorable for the development of the Madden–Julian oscillation (MJO) was investigated by classifying MJO-like atmospheric patterns as MJO and regionally confined convective (RCC) events. Comparison of MJO and RCC events showed that even when preceded by a major convective suppression event, convective events did not develop into an MJO when large-scale buildup of moist static energy (MSE) was inhibited. The difference in the MSE accumulation between MJO and RCC is related to the contrasting low-frequency basic-state sea surface temperature (SST) pattern; the MJO and RCC events were associated with anomalously warm and cold low-frequency SSTs prevailing over the western to central Pacific, respectively. Differences in the SST anomaly field were absent from the intraseasonal frequency range of 20–60 days. The basic-state SST pattern associated with the MJO was characterized by a positive zonal SST gradient from the Indian Ocean to the western Pacific, which provided a long-standing condition that allowed for sufficient buildup of MSE across the Indian Ocean to the western Pacific via large-scale low-level convergence over intraseasonal and longer time scales. The results of this study suggest the importance of such a basic-state SST, with a long-lasting positive zonal SST gradient, for enhancing convection over a longer than intraseasonal time scale in realizing a complete MJO life cycle.

scholarly journals Modulation of North Pacific Tropical Cyclone Activity by Three Phases of ENSO

2011 ◽  
Vol 24 (6) ◽  
pp. 1839-1849 ◽  
Author(s):  
Hye-Mi Kim ◽  
Peter J. Webster ◽  
Judith A. Curry
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Wind Shear ◽  
Monsoon Trough ◽  
Western Pacific ◽  
Northwestern Part ◽  
Westerly Wind ◽  
Central Pacific ◽  
East Pacific ◽  
The Western Pacific

Abstract Tropical Pacific Ocean warming has been separated into two modes based on the spatial distribution of the maximum sea surface temperature (SST) anomaly: an east Pacific warming (EPW) and a central Pacific warming (CPW). When combined with east Pacific cooling (EPC), these three regimes are shown to have different impacts on tropical cyclone (TC) activity over the North Pacific by differential modulation of both local thermodynamic factors and large-scale circulation patterns. In EPW years, the genesis and the track density of TCs tend to be enhanced over the southeastern part and suppressed in the northwestern part of the western Pacific by strong westerly wind shear. The extension of the monsoon trough and the weak wind shear over the central Pacific increases the likelihood of TC activity to the east of the climatological mean TC genesis location. In CPW years, the TC activity is shifted to the west and is extended through the northwestern part of the western Pacific. The westward shifting of CPW-induced heating moves the anomalous westerly wind and monsoon trough through the northwestern part of the western Pacific and provides a more favorable condition for TC landfall. The CPW, on the other hand, produces a large suppression of TC activity in the eastern Pacific basin. In EPC years, all of the variables investigated show almost a mirror image of the EPW.

Change in Coherence of Summer Rainfall Variability over the Western Pacific around the Early 2000s: ENSO Influence

2020 ◽  
Vol 33 (3) ◽  
pp. 1105-1119 ◽  
Author(s):  
Zhuoqi He ◽  
Weiqiang Wang ◽  
Renguang Wu ◽  
In-Sik Kang ◽  
Chao He ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Rainfall Anomaly ◽  
Western Pacific ◽  
Northern Indian Ocean ◽  
Central Pacific ◽  
Enso Events ◽  
The Western Pacific ◽  
Sst Anomalies

AbstractThis study is the second part of a two-part series investigating a recent decadal modulation of interannual variability over the western Pacific Ocean around the early 2000s. Observational evidence shows that the anomalous Philippine Sea cyclonic circulation retreats eastward, with the western Pacific rainfall anomaly distribution changing from a north–south tripole pattern to an east–west dipole pattern after 2003–04. These changes are attributed to a change in El Niño–Southern Oscillation (ENSO) properties and the associated Indo-Pacific sea surface temperature (SST) anomaly pattern. Before the early 2000s, slow-decaying ENSO events induce large SST anomalies in the northern Indian Ocean during the following summer. The northern Indian Ocean SST anomalies act together with the opposite-sign SST anomalies in the tropical central Pacific, leading to a zonally extended anomalous lower-level cyclonic (anticyclonic) circulation and an elongated rainfall anomaly band over the western Pacific. After the early 2000s, ENSO events have a shortened period and a weakened amplitude, and the eastern Pacific SST anomalies tend to undergo a phase transition from winter to summer. Consequently, the influence of ENSO on the Indian Ocean SST anomalies is weakened and the contribution of the northern Indian Ocean SST anomalies to the western Pacific summer rainfall variability becomes insignificant. In this case, the western North Pacific summer rainfall is mainly dominated by the well-developed tropical Pacific SST forcing following the early decay of ENSO events. The potential physical mechanism for the two types of ENSO influences is validated with regional decoupled Community Earth System Model experiments.

Recent Changes in ENSO Teleconnection over the Western Pacific Impacts the Eastern China Precipitation Dipole

2016 ◽  
Vol 29 (21) ◽  
pp. 7587-7598 ◽  
Author(s):  
Dachao Jin ◽  
Saji N. Hameed ◽  
Liwei Huo
Keyword(s):  
Eastern China ◽  
Tropical Pacific ◽  
The Other ◽  
Western Pacific ◽  
Asia Pacific ◽  
Boreal Summer ◽  
Central Pacific ◽  
Western Tropical Pacific ◽  
Enso Teleconnections ◽  
The Western Pacific

Abstract The eastern China precipitation dipole (ECPD) features an out-of-phase relationship between boreal summer precipitation over the middle and lower reaches of the Yangtze River and the Hetao region to its northwest. The precipitation dipole is strongly influenced by ENSO teleconnections over the western tropical Pacific. Here it is shown that a pronounced weakening of both the rainfall variability over eastern China as well as the precipitation dipole structure occurred around the mid-1990s. The changes have been analyzed by considering two epochs: one during 1979–95 and the other during 1996–2009. The characteristic feature of the circulation anomaly during the first epoch is the well-known East Asia–Pacific/Pacific–Japan (EAP/PJ) pattern, a quasi-meridional teleconnection pattern emanating from the western tropical Pacific. On the other hand, during the latter epoch eastern China precipitation variability occurs as an integral part of the circulation anomalies over the western Pacific. In contrast to the more meridionally restricted anomalies during canonical ENSO episodes, the western Pacific circulation has a significantly larger meridional scale. Intriguingly correlation of the precipitation dipole with Pacific sea surface temperature flips in sign during the second epoch, with enhanced precipitation over southeastern China associated with La Niña–like variability, in contrast to the co-occurrence of enhanced precipitation over this region with El Niño during the first epoch. The results suggest that the dominance of Modoki or central Pacific El Niños, and the altered structure of ENSO teleconnections associated with these, may play a role in the weakened ECPD structure during the latter epoch.

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