scholarly journals The seasonal relationship between intraseasonal tropical variability and ENSO in CMIP5

2018 ◽  
Vol 11 (6) ◽  
pp. 2373-2392 ◽  
Author(s):  
Tatiana Matveeva ◽  
Daria Gushchina ◽  
Boris Dewitte
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Ocean Dynamics ◽  
Central Pacific ◽  
Tropical Variability ◽  
Large Dispersion ◽  
Enso Diversity ◽  
Intraseasonal Tropical Variability

Abstract. The El Niño–Southern Oscillation (ENSO) is tightly linked to the intraseasonal tropical variability (ITV) that contributes to energise the deterministic ocean dynamics during the development of El Niño. Here, the relationship between ITV and ENSO is assessed based on models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) taking into account the so-called diversity of ENSO, that is, the existence of two types of events (central Pacific versus eastern Pacific El Niño). As a first step, the models' skill in simulating ENSO diversity is assessed. The characteristics of the ITV are then documented revealing a large dispersion within an ensemble of 16 models. A total of 11 models exhibit some skill in simulating the key aspects of the ITV for ENSO: the total variance along the Equator, the seasonal cycle and the characteristics of the propagation along the Equator of the Madden–Julian oscillation (MJO) and the convectively coupled equatorial Rossby (ER) waves. Five models that account realistically for both the two types of El Niño events and ITV characteristics are used for the further analysis of seasonal ITV ∕ ENSO relationship. The results indicate a large dispersion among the models and an overall limited skill in accounting for the observed seasonal ITV ∕ ENSO relationship. Implications of our results are discussed in light of recent studies on the forcing mechanism of ENSO diversity.

scholarly journals The relationship between intraseasonal tropical variability and ENSO and its modulation at seasonal to decadal timescales

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
Daria Gushchina ◽  
Boris Dewitte
Keyword(s):  
El Niño ◽  
General Circulation ◽  
Rossby Waves ◽  
El Nino ◽  
General Circulation Models ◽  
Wave Radiation ◽  
Boreal Summer ◽  
Central Pacific ◽  
Tropical Variability ◽  
Intraseasonal Tropical Variability

AbstractThe intraseasonal tropical variability (ITV) patterns in the tropical troposphere are documented using double space-time Fourier analysis. Madden and Julian oscillations (MJO) as well as equatorial coupled waves (Kelvin and Rossby) are investigated based on the NCEP/NCAR Reanalysis data for the 1977–2006 period and the outputs of an intermediate ocean-atmosphere coupled model named LODCA-OTCM. A strong seasonal dependence of the ITV/ENSO relationship is evidenced. The leading relationship for equatorial Rossby waves (with the correlation of the same order than for the MJO) is documented; namely, it is shown that intensification of Rossby waves in the central Pacific during boreal summer precedes by half a year the peak of El Niño. The fact that MJO activity in spring-summer is associated to the strength of subsequent El Niño is confirmed. It is shown that LODCA-QTCM is capable of simulating the convectively coupled equatorial waves in outgoing long wave radiation and zonal wind at 850 hPa fields with skill comparable to other Coupled General Circulation Models. The ITV/ENSO relationship is modulated at low frequency. In particular the periods of low ENSO amplitude are associated with weaker MJO activity and a cancellation of MJO at the ENSO development phase. In opposition, during the decaying phase, MJO signal is strong. The periods of strong ENSO activity are associated with a marked coupling between MJO, Kelvin and equatorially Rossby waves and ENSO; the precursor signal of MJO (Rossby waves) in the western (central) Pacific is obvious. The results provide material for the observed change in ENSO characteristics in recent years and question whether the characteristics of the ITV/ENSO relationship may be sensitive to the observed warming in the central tropical Pacific.

scholarly journals Effects of Tropical Cyclones on ENSO

2019 ◽  
Vol 32 (19) ◽  
pp. 6423-6443 ◽  
Author(s):  
Tao Lian ◽  
Jun Ying ◽  
Hong-Li Ren ◽  
Chan Zhang ◽  
Ting Liu ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Coupled Model ◽  
Enso Event ◽  
Central Pacific ◽  
Final State ◽  
Enso Dynamics

AbstractNumerous studies have investigated the role of El Niño–Southern Oscillation (ENSO) in modulating the activity of tropical cyclones (TCs) in the western Pacific on interannual time scales, but the effects of TCs on ENSO are less discussed. Some studies have found that TCs sharply increase surface westerly anomalies over the equatorial western–central Pacific and maintain them there for a few days. Given the strong influence of equatorial surface westerly wind bursts on ENSO, as confirmed by much recent literature, the effects of TCs on ENSO may be much greater than previously expected. Using recently released observations and reanalysis datasets, it is found that the majority of near-equatorial TCs (simply TCs hereafter) are associated with strong westerly anomalies at the equator, and the number and longitude of TCs are significantly correlated with ENSO strength. When TC-related wind stresses are added into an intermediate coupled model, the simulated ENSO becomes more irregular, and both ENSO magnitude and skewness approach those of observations, as compared with simulations without TCs. Adding TCs into the model system does not break the linkage between the heat content anomaly and subsequent ENSO event in the model, which manifest the classic recharge–discharge ENSO dynamics. However, the influence of TCs on ENSO is so strong that ENSO magnitude and sometimes its final state—that is, either El Niño or La Niña—largely depend on the number and timing of TCs during the event year. Our findings suggest that TCs play a prominent role in ENSO dynamics, and their effects must be considered in ENSO forecast models.

scholarly journals Will There Be a Significant Change to El Niño in the Twenty-First Century?

2012 ◽  
Vol 25 (6) ◽  
pp. 2129-2145 ◽  
Author(s):  
Samantha Stevenson ◽  
Baylor Fox-Kemper ◽  
Markus Jochum ◽  
Richard Neale ◽  
Clara Deser ◽  
...  
Keyword(s):  
Climate Change ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Ocean Dynamics ◽  
First Century ◽  
Climate System Model ◽  
Enso Variability ◽  
Tropical Variability ◽  
Twenty First Century

Abstract The El Niño–Southern Oscillation (ENSO) response to anthropogenic climate change is assessed in the following 1° nominal resolution Community Climate System Model, version 4 (CCSM4) Coupled Model Intercomparison Project phase 5 (CMIP5) simulations: twentieth-century ensemble, preindustrial control, twenty-first-century projections, and stabilized 2100–2300 “extension runs.” ENSO variability weakens slightly with CO2; however, various significance tests reveal that changes are insignificant at all but the highest CO2 levels. Comparison with the 1850 control simulation suggests that ENSO changes may become significant on centennial time scales; the lack of signal in the twentieth- versus twenty-first-century ensembles is due to their limited duration. Changes to the mean state are consistent with previous studies: a weakening of the subtropical wind stress curl, an eastward shift of the tropical convective cells, a reduction in the zonal SST gradient, and an increase in vertical thermal stratification take place as CO2 increases. The extratropical thermocline deepens throughout the twenty-first century, with the tropical thermocline changing slowly in response. The adjustment time scale is set by the relevant ocean dynamics, and the delay in its effect on ENSO variability is not diminished by increasing ensemble size. The CCSM4 results imply that twenty-first-century simulations may simply be too short for identification of significant tropical variability response to climate change. An examination of atmospheric teleconnections, in contrast, shows that the remote influences of ENSO do respond rapidly to climate change in some regions, particularly during boreal winter. This suggests that changes to ENSO impacts may take place well before changes to oceanic tropical variability itself become significant.

scholarly journals Improvement of ENSO Simulation Based on Intermodel Diversity

2015 ◽  
Vol 28 (3) ◽  
pp. 998-1015 ◽  
Author(s):  
Yoo-Geun Ham ◽  
Jong-Seong Kug
Keyword(s):  
Interannual Variability ◽  
El Niño ◽  
Climate Models ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Coupled Model ◽  
Global Climate Models ◽  
Climate Simulation ◽  
Central Pacific

Abstract In this study, a new methodology is developed to improve the climate simulation of state-of-the-art coupled global climate models (GCMs), by a postprocessing based on the intermodel diversity. Based on the close connection between the interannual variability and climatological states, the distinctive relation between the intermodel diversity of the interannual variability and that of the basic state is found. Based on this relation, the simulated interannual variabilities can be improved, by correcting their climatological bias. To test this methodology, the dominant intermodel difference in precipitation responses during El Niño–Southern Oscillation (ENSO) is investigated, and its relationship with climatological state. It is found that the dominant intermodel diversity of the ENSO precipitation in phase 5 of the Coupled Model Intercomparison Project (CMIP5) is associated with the zonal shift of the positive precipitation center during El Niño. This dominant intermodel difference is significantly correlated with the basic states. The models with wetter (dryer) climatology than the climatology of the multimodel ensemble (MME) over the central Pacific tend to shift positive ENSO precipitation anomalies to the east (west). Based on the model’s systematic errors in atmospheric ENSO response and bias, the models with better climatological state tend to simulate more realistic atmospheric ENSO responses. Therefore, the statistical method to correct the ENSO response mostly improves the ENSO response. After the statistical correction, simulating quality of the MME ENSO precipitation is distinctively improved. These results provide a possibility that the present methodology can be also applied to improving climate projection and seasonal climate prediction.

scholarly journals Impact of westerly wind burst on El Niño-sourthern oscillation

2020 ◽  
Author(s):  
◽  
Mohammad Alam
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Vital Role ◽  
Tropical Pacific ◽  
Westerly Wind ◽  
Central Pacific ◽  
Enso Events ◽  
The Tropical Pacific

Westerly wind bursts (WWBs), usually occurring in the tropical Pacific region, play a vital role in El Niño–Southern Oscillation (ENSO). In this study, we use a hybrid coupled model (HCM) for the tropical Pacific Ocean-atmosphere system to investigate WWBs impact on ENSO. To achieve this goal, two experiments are performed: (a) first, the standard version of the HCM is integrated for years without prescribed WWBs events; and (b) second, the WWBs are added into the HCM (HCM-WWBs). Results show that HCM-WWBs can generate not only more realistic climatology of sea surface temperature (SST) in both spatial structure and temporal amplitudes, but also better ENSO features, than the HCM. In particular, the HCM-WWBs can capture the central Pacific (CP) ENSO events, which is absent in original HCM. Furthermore, the possible physical mechanisms responsible for these improvements by WWBs are discussed.

Ocean dynamics are key to extratropical forcing of El Niño

2021 ◽  
pp. 1-34
Author(s):  
Soumi Chakravorty ◽  
Renellys C. Perez ◽  
Bruce T. Anderson ◽  
Sarah M. Larson ◽  
Benjamin S. Giese ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Ocean Dynamics ◽  
Positive Phase ◽  
Trade Wind ◽  
Atmospheric Variability ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Extratropical Forcing

AbstractThe El Niño/Southern Oscillation (ENSO) has been recently linked with extratropical-Pacific atmospheric variability. The two key mechanisms connecting the atmospheric variability of extratropical-Pacific with ENSO are the heat-flux driven “seasonal footprinting mechanism” (SFM) and the ocean-dynamics driven “trade wind charging” (TWC) mechanism. However, their relative contributions to ENSO are still unknown. Here we present modeling evidence that the positive phase of the SFM generates a weaker, short-lived central Pacific El Niño-like warming pattern in the fall, whereas the TWC positive phase leads to a wintertime eastern Pacific El Niño-like warming. When both mechanisms are active, a strong, persistent El Niño develops. While both mechanisms can trigger equatorial wind anomalies that generate an El Niño, the strength and persistence of the warming depends on the subsurface heat content buildup by the TWC mechanism. These results suggest that while dynamical-coupling associated with extratropical forcing is crucial to maintain an El Niño, thermodynamical-coupling is an extratropical source of El Niño diversity.

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 Two Leading ENSO Modes and El Niño Types in the Zebiak–Cane Model

2018 ◽  
Vol 31 (5) ◽  
pp. 1943-1962 ◽  
Author(s):  
Ruihuang Xie ◽  
Fei-Fei Jin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Coupled Model ◽  
Warm Pool ◽  
Central Pacific ◽  
El Niño Events ◽  
Instrumental Records ◽  
El Nino Events

Modern instrumental records reveal that El Niño events differ in their spatial patterns and temporal evolutions. Attempts have been made to categorize them roughly into two main types: eastern Pacific (EP; or cold tongue) and central Pacific (CP; or warm pool) El Niño events. In this study, a modified version of the Zebiak–Cane (MZC) coupled model is used to examine the dynamics of these two types of El Niño events. Linear eigenanalysis of the model is conducted to show that there are two leading El Niño–Southern Oscillation (ENSO) modes with their SST patterns resembling those of two types of El Niño. Thus, they are referred to as the EP and CP ENSO modes. These two modes are sensitive to changes in the mean states. The heat budget analyses demonstrate that the EP (CP) mode is dominated by thermocline (zonal advective) feedback. Therefore, the weak (strong) mean wind stress and deep (shallow) mean thermocline prefer the EP (CP) ENSO mode because of the relative dominance of thermocline (zonal advective) feedback under such a mean state. Consistent with the linear stability analysis, the occurrence ratio of CP/EP El Niño events in the nonlinear simulations generally increases toward the regime where the linear CP ENSO mode has relatively higher growth rate. These analyses suggest that the coexistence of two leading ENSO modes is responsible for two types of El Niño simulated in the MZC model. This model result may provide a plausible scenario for the observed ENSO diversity.

scholarly journals The relationship between intraseasonal tropical variability and ENSO simulated by the CMIP5

2017 ◽  
Author(s):  
Tatiana Matveeva ◽  
Daria Gushchina
Keyword(s):  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Southern Oscillation ◽  
Relative Size ◽  
Phase Lag ◽  
Intergovernmental Panel ◽  
Tropical Variability ◽  
Intraseasonal Tropical Variability ◽  
Equatorial Rossby Waves

Abstract. This study evaluates the simulation of relationship between intraseasonal tropical variability (ITV) and El Niño Southern Oscillation (ENSO) in 23 models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). As a first step, the models' skill in simulating ENSO diversity is assessed, which indicates that 16 models among 23 are able to simulate realistically the statistics of the relative size of two types of El Niño. The characteristics of the ITV are then documented revealing that only five models (CMCC-CM, CCSM4, BNU-ESM, INMCM4 and MIROC5) simulate realistically the parameters crucial for proper reproducing of ITV contribution to the El Niño, in particular the total variability, seasonal cycle and propagation along the equator of Madden-Julian oscillation (MJO) and convectively coupled equatorial Rossby waves (ER). At last step the ITV/ENSO relationship in the models are analyzed and compared to observation. It is shown that the key aspects of this interaction such as phase lag between ITV peak activity and El Niño peak and longitude localization of maximum correlation between ITV and ENSO is realistically simulated by CMCC-CM and MIROC5 for MJO and CMCC-CM and INMCM4 for equatorial Rossby waves. These models are capable to reproduce the distinct MJO and ER behavior associated to the two El Niño flavors. Aforementioned models may be used for the investigation of the sensitivity of the ITV/ENSO seasonal dependence to global warming.

scholarly journals Understanding Key Roles of Two ENSO Modes in Spatiotemporal Diversity of ENSO

2020 ◽  
Vol 33 (15) ◽  
pp. 6453-6469 ◽  
Author(s):  
Run Wang ◽  
Hong-Li Ren
Keyword(s):  
Spatial Patterns ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
High Amplitude ◽  
Life Cycles ◽  
Ocean Dynamics ◽  
Central Pacific ◽  
Enso Events

AbstractEl Niño–Southern Oscillation (ENSO) events exhibit a diversity of amplitudes, spatial patterns, and life cycles, with the main ENSO periods concentrated in the 3–7-yr [low-frequency (LF)] and 2–3-yr [quasi-biennial (QB)] bands. In this study, the spatiotemporal diversity of ENSO is quantitatively examined by extracting the two ENSO modes, namely, the LF and QB components of ENSO, from the traditional Niño-3.4 index and connecting them with the spatial types of ENSO. El Niño events can be regrouped as the QB-dominated central-Pacific ENSO-like (QB-CP), LF-dominated eastern-Pacific ENSO-like (LF-EP), and LF-dominated mixing (LF-mixing) types. La Niña events with vague spatial patterns can also have the same categorization. The QB-CP and LF-EP El Niño types both have a high-amplitude QB component. Meanwhile, the former is less affected by its powerless LF component, but the latter is controlled by its strong LF component. Ocean dynamics of the two El Niño types are distinct from each other. The thermocline feedback dominates the growth of the two El Niño types and contributes to the phase transition of the LF-EP type, while the zonal advective feedback is of increasing importance in the QB-CP El Niño and mainly contributes to the phase transitions of the two El Niño types. Additionally, the LF-mixing type with ambiguous spatial features and complex life cycles is distinguished from the other two types. These results indicate that the two ENSO modes coexist in the tropical Pacific air–sea system, and their combination with changing amplitude is the key to explaining the spatiotemporal diversity of ENSO.

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