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  • American Meteorological Society  (9)
  • 2005-2009  (9)
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  • American Meteorological Society  (9)
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  • 2005-2009  (9)
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  • 1
    Online Resource
    Online Resource
    Two Types of El Niño Events: Cold Tongue El Niño and Warm Pool El Niño
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 6 ( 2009-03-15), p. 1499-1515
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 6 ( 2009-03-15), p. 1499-1515
    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.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2008JCLI2624.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    El Niño–La Niña Asymmetry in the Coupled Model Intercomparison Project Simulations*
    American Meteorological Society ; 2005
    In:  Journal of Climate Vol. 18, No. 14 ( 2005-07-15), p. 2617-2627
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 18, No. 14 ( 2005-07-15), p. 2617-2627
    Abstract: The El Niño–La Niña asymmetry was estimated in the 10 different models participating in the Coupled Model Intercomparison Project (CMIP). Large differences in the “asymmetricity” (a variance-weighted skewness) of SST anomalies are found between models and observations. Most of the coupled models underestimate the nonlinearity and only a few exhibit the positively skewed SST anomalies over the tropical eastern Pacific as seen in the observation. A significant association between the nonlinear dynamical heating (NDH) and asymmetricity in the model–ENSO indices is found, inferring that asymmetricity is caused mainly by NDH. Among the 10 models, one coupled GCM simulates the asymmetricity of the tropical SST realistically, and its simulation manifests a strong relationship between the intensity and the propagating feature of ENSO—the strong ENSO events moving eastward and the weak ENSO events moving westward—which is consistent with the observation. Interestingly, the coupled general circulation models, of which the ocean model is based on the one used by Bryan and Cox, commonly showed the reasonably positive skewed ENSO. The decadal changes in the skewness, variance, and NDH of the model-simulated ENSO are also observed. These three quantities over the tropical eastern Pacific are significantly correlated to each other, indicating that the decadal change in ENSO variability is closely related to the nonlinear process of ENSO. It is also found that these decadal changes in ENSO variability are related to the decadal variation in the tropical Pacific SST, implying that the decadal change in the El Niño–La Niña asymmetry could manifest itself as a rectified change in the background state.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI3433.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    Interannual Variations of the Tropical Ocean Instability Wave and ENSO
    American Meteorological Society ; 2008
    In:  Journal of Climate Vol. 21, No. 15 ( 2008-08-01), p. 3680-3686
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 21, No. 15 ( 2008-08-01), p. 3680-3686
    Abstract: Using ocean data assimilation products, variability of eastern Pacific Ocean tropical instability waves (TIWs) and their interaction with the El Niño–Southern Oscillation (ENSO) were analyzed. TIWs are known to heat the cold tongue through horizontal advection. Conversely, variability of the cold tongue influences TIW variability (TIWV). During La Niña, TIWs are more active and contribute to anomalous warming. During El Niño, TIWs are suppressed and induce an anomalous cooling. TIWV thus acts as negative feedback to ENSO. Interestingly, this feedback is stronger during La Niña than during El Niño. To investigate this negative/asymmetric feedback, a simple parameterization for the horizontal thermal flux convergence due to TIWs was incorporated into a simple ENSO model. The model results suggested that asymmetric thermal heating associated with TIWs can explain the El Niño–La Niña asymmetry (with larger-amplitude El Niños).
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2008JCLI1701.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
    Online Resource
    Online Resource
    The Influence of ENSO on the Generation of Decadal Variability in the North Pacific*
    American Meteorological Society ; 2007
    In:  Journal of Climate Vol. 20, No. 4 ( 2007-02-15), p. 667-680
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 20, No. 4 ( 2007-02-15), p. 667-680
    Abstract: This diagnostic study explores the generation of decadal variability in the North Pacific resulting from the asymmetry of the El Niño–Southern Oscillation phenomenon and the nonlinearity of the atmospheric tropical–extratropical teleconnection. Nonlinear regression analysis of the North Pacific sea surface temperatures and atmospheric fields with respect to the ENSO index reveals that the main teleconnection centers shift between El Niño and La Niña years. This asymmetry in the ENSO response, together with the skewed probabilistic distribution of ENSO itself, may contribute to the generation of the long-term decadal variability of sea surface temperatures in the extratropical North Pacific. It is argued that this hypothesis may explain the significant variance of the observed Pacific decadal oscillation in the extratropics.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI4017.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 5
    Online Resource
    Online Resource
    Successive Modulation of ENSO to the Future Greenhouse Warming
    American Meteorological Society ; 2008
    In:  Journal of Climate Vol. 21, No. 1 ( 2008-01-01), p. 3-21
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 21, No. 1 ( 2008-01-01), p. 3-21
    Abstract: The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2007JCLI1500.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Interactive Feedback between the Tropical Pacific Decadal Oscillation and ENSO in a Coupled General Circulation Model
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 24 ( 2009-12-15), p. 6597-6611
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 24 ( 2009-12-15), p. 6597-6611
    Abstract: The output from a coupled general circulation model (CGCM) is used to develop evidence showing that the tropical Pacific decadal oscillation can be driven by an interaction between the El Niño–Southern Oscillation (ENSO) and the slowly varying mean background climate state. The analysis verifies that the decadal changes in the mean states are attributed largely to decadal changes in ENSO statistics through nonlinear rectification. This is seen because the time evolutions of the first principal component analysis (PCA) mode of the decadal-varying tropical Pacific SST and the thermocline depth anomalies are significantly correlated to the decadal variations of the ENSO amplitude (also skewness). Its spatial pattern resembles the residuals of the SST and thermocline depth anomalies after there is uneven compensation from El Niño and La Niña events. In addition, the stability analysis of a linearized intermediate ocean–atmosphere coupled system, for which the background mean states are specified, provides qualitatively consistent results compared to the CGCM in terms of the relationship between changes in the background mean states and the characteristics of ENSO. It is also shown from the stability analysis as well as the time integration of a nonlinear version of the intermediate coupled model that the mean SST for the high-variability ENSO decades acts to intensify the ENSO variability, while the mean thermocline depth for the same decades acts to suppress the ENSO activity. Thus, there may be an interactive feedback consisting of a positive feedback between the ENSO activity and the mean state of the SST and a negative feedback between the ENSO activity and the mean state of the thermocline depth. This feedback may lead to the tropical decadal oscillation, without the need to invoke any external mechanisms.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2009JCLI2782.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    The Forced and Intrinsic Low-Frequency Modes in the North Pacific*
    American Meteorological Society ; 2005
    In:  Journal of Climate Vol. 18, No. 6 ( 2005-03-15), p. 876-885
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 18, No. 6 ( 2005-03-15), p. 876-885
    Abstract: Conditional maximum covariance analysis is applied to investigate the coherent patterns between the tropical and North Pacific SST and the North Pacific 500-hPa geopotential height anomalies. Two leading modes are identified. One is an intrinsic midlatitude mode, the North Pacific (NP) mode, for which SST anomalies are mainly confined to the extratropical North Pacific. The other is a tropical ocean–atmosphere coupled mode, the ENSO mode, in which an ENSO-like SST pattern dominates the Tropics but extratropical SST anomalies are relatively weak. The NP and ENSO modes exhibit distinct spatial and temporal characteristics. For the NP mode, atmospheric variation leads to changes in SST, while for the ENSO mode the opposite is true. The NP mode displays a persistence barrier during August–September whereas the ENSO mode has a March–April persistence barrier. The upper-tropospheric jet stream associated with the NP and ENSO mode intensifies, respectively, over the central North Pacific and the subtropical northeastern Pacific; consequently, the transient activities maximize in their corresponding jet exit regions. The expansion coefficients of the 500-hPa geopotential height associated with the two modes appear to be significantly correlated. However, by reducing the high-frequency part (e.g., shorter than the interannual time scale) in expansion coefficients, the correlation becomes insignificant, indicating that the significant correlation results from high-frequency signals that are unrelated to the corresponding SST variation. The results presented here suggest that the intrinsic coupled mode in the midlatitude North Pacific may be distinguished from the forced mode by remote ENSO, especially on the interannual time scale.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI-3298.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 8
    Online Resource
    Online Resource
    Interaction between Near-Annual and ENSO Modes in a CGCM Simulation: Role of the Equatorial Background Mean State
    American Meteorological Society ; 2007
    In:  Journal of Climate Vol. 20, No. 6 ( 2007-03-15), p. 1035-1052
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 20, No. 6 ( 2007-03-15), p. 1035-1052
    Abstract: A 260-yr-long coupled general circulation model (CGCM) simulation is used to investigate the interaction between ENSO mode and near-annual variability and its sensitivity to the equatorial background mean stratification and seasonal cycles. Although the thermocline mean vertical structure of the model favors the high-order baroclinic modes that are associated with the slow time scales of the coupled variability, the simulated ENSO oscillates at a dominant quasi-biennial frequency. Biases of the climatological velocity field are favorable to the dominance of the zonal advective feedback over the thermocline feedback, the model exhibiting an overenergetic westward seasonal zonal current in the central-western equatorial Pacific, and an upwelling rate that is about half the observations. This sets the conditions for the enhancement of a near-annual mode that is observed to oscillate at an 8-month period in the model. Using an intermediate coupled model of the tropical Pacific where the climatological fields are prescribed to the ones derived from the CGCM, it is demonstrated that the quasi-biennial ENSO variability simulated by the CGCM is mostly due to the biases in the climatological currents of the CGCM. These biases favor the dominance of the fast “zonal advective feedback” over the slow “thermocline feedback” in the coupled system and enhance a fast coupled basin mode. This fast mode differs from the theoretical Pacific Ocean basin mode in that, besides mean temperature advection by the zonal current anomalies, it is also driven by anomalous temperature advection by the total current. Results suggest that the near-annual mode destabilizes the ENSO mode to produce overenergetic quasi-biennial oscillations in the model. It also contributes to the ENSO asymmetry and the cold bias of the CGCM mean state by nonlinear accumulation of temperature zonal advection, which works toward the cold in the western Pacific more than the warm in the east. It is suggested that the model equilibrium results from the interaction between the ENSO mode, the near-annual mode, and the mean state.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI4060.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 9
    Online Resource
    Online Resource
    A Nonlinear Analysis of the ENSO Cycle and Its Interdecadal Changes*
    American Meteorological Society ; 2005
    In:  Journal of Climate Vol. 18, No. 16 ( 2005-08-15), p. 3229-3239
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 18, No. 16 ( 2005-08-15), p. 3229-3239
    Abstract: The nonlinear principal component analysis (NLPCA), via a neural network approach, was applied to thermocline anomalies in the tropical Pacific. While the tropical sea surface temperature (SST) anomalies had been nonlinearly mapped by the NLPCA mode 1 onto an open curve in the data space, the thermocline anomalies were mapped to a closed curve, suggesting that ENSO is a cyclic phenomenon. The NLPCA mode 1 of the thermocline anomalies reveals the nonlinear evolution of the ENSO cycle with much asymmetry for the different phases: The weak heat accumulation in the whole equatorial Pacific is followed by the strong El Niño, and the subsequent strong drain of equatorial heat content toward the off-equatorial region precedes a weak La Niña. This asymmetric ENSO evolution implies that the nonlinear instability enhances the growth of El Niño, but dwarfs the growth of La Niña. The nonlinear ENSO cycle was found to have changed since the late 1970s. For the pre-1980s the ENSO cycle associated with the thermocline is less asymmetrical than that during the post-1980s, indicating that the nonlinearity of the ENSO cycle has become stronger since the late 1970s.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI3466.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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