scholarly journals Integrating Ocean Subsurface Temperatures in Statistical ENSO Forecasts

2005 ◽  
Vol 18 (17) ◽  
pp. 3571-3586 ◽  
Author(s):  
Jose Eric Ruiz ◽  
Ian Cordery ◽  
Ashish Sharma
Keyword(s):  
Southern Oscillation ◽  
Heat Content ◽  
Enso Event ◽  
Empirical Orthogonal Functions ◽  
Boreal Winter ◽  
Orthogonal Functions ◽  
Subsurface Ocean ◽  
Prediction Scheme ◽  
Cold Events ◽  
The Tropical Pacific

Abstract Subsurface characteristics of oceans have recently become of interest to climate modelers. Here subsurface information has been linked to the evolution of the El Niño–Southern Oscillation (ENSO) in a simple statistical formulation. The hypothesis proposed is that the inclusion of subsurface ocean heat content in a persistence-based representation of ENSO results in an increase in prediction skill. The subsurface temperature field is represented by anomalies in the 20°C isotherm (Z20) in the Indian and Pacific Oceans. Using a cross-validation approach, the first two empirical orthogonal functions (EOFs) of the Z20 anomalies are derived, but only the second EOF is used as a predictor. The first EOF is found to be representative of the mature ENSO signal while the second EOF shows characteristics that are precursory to an ENSO event. When included in a persistence-based prediction scheme, the second EOF enhances the skill of ENSO hindcasts up to a lead time of 15 months. Results are compared with another model that uses the second EOF of the SST anomalies in the tropical Pacific Ocean and persistence as predictors. Cross-validated hindcasts from the isotherm-based scheme are generally more skillful than those obtained from the persistence and SST-based prediction schemes. Hindcasts of cold events are particularly close to the observed values even at long lags. Major improvements occur for predictions made during boreal winter and spring months when the addition of subsurface information resulted in predictions that are not greatly affected by the damping effect of the “spring barrier.”

An Assessment of Differences in ENSO Mechanisms in a Coupled GCM Simulation

2006 ◽  
Vol 19 (1) ◽  
pp. 69-87 ◽  
Author(s):  
Francisco Alvarez-Garcia ◽  
William Cabos Narvaez ◽  
Maria J. Ortiz Bevia
Keyword(s):  
Local Development ◽  
Southern Oscillation ◽  
Heat Content ◽  
Propagation Characteristic ◽  
Tropical Pacific ◽  
Wind Stress Curl ◽  
Coupled Gcm ◽  
Physical Mechanisms ◽  
Cold Events ◽  
The Tropical Pacific

Abstract This study investigates the physical mechanisms involved in the generation and decay of El Niño–Southern Oscillation episodes in a coupled GCM simulation. Warm and cold events found in a 100-yr-long record are separated into groups by means of a clustering technique that objectively discriminates common features in the evolution of the tropical Pacific heat content anomalies leading to the event’s peak. Through an analysis of the composites obtained from this classification, insight is gained as to the processes responsible for the presence of different behaviors. Three classes of warm events were identified. The first is characterized by the westward propagation of warm heat content anomalies north of the equator before the onset of the episode. This propagation characteristic of the delayed oscillator paradigm appears weakened in the decay of the episode. In the second class, local development of heat content anomalies in the northwest tropical Pacific, associated with overlying wind stress curl anomalies, dominates both the generation and the decay of the warm event. In addition, subsurface cold anomalies form in the equatorial western Pacific in association with the poleward flow considered by the recharge–discharge oscillator model. The third class is characterized by a relatively quick development of the warm episode. Attention is focused on the first two classes. The suitability of different conceptual models to explain them is addressed. Previous analyses of the simulation are reviewed throughout this work. Differences between the classes are related to a regime shift that occurs toward the middle of the record.

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 A Hierarchy of Data-Based ENSO Models

2005 ◽  
Vol 18 (21) ◽  
pp. 4425-4444 ◽  
Author(s):  
D. Kondrashov ◽  
S. Kravtsov ◽  
A. W. Robertson ◽  
M. Ghil
Keyword(s):  
El Niño ◽  
Additive Noise ◽  
Polynomial Regression ◽  
El Nino ◽  
Southern Oscillation ◽  
Model Performance ◽  
Empirical Orthogonal Functions ◽  
Quadratic Model ◽  
Orthogonal Functions ◽  
Optimizing Model

Abstract Global sea surface temperature (SST) evolution is analyzed by constructing predictive models that best describe the dataset’s statistics. These inverse models assume that the system’s variability is driven by spatially coherent, additive noise that is white in time and are constructed in the phase space of the dataset’s leading empirical orthogonal functions. Multiple linear regression has been widely used to obtain inverse stochastic models; it is generalized here in two ways. First, the dynamics is allowed to be nonlinear by using polynomial regression. Second, a multilevel extension of classic regression allows the additive noise to be correlated in time; to do so, the residual stochastic forcing at a given level is modeled as a function of variables at this level and the preceding ones. The number of variables, as well as the order of nonlinearity, is determined by optimizing model performance. The two-level linear and quadratic models have a better El Niño–Southern Oscillation (ENSO) hindcast skill than their one-level counterparts. Estimates of skewness and kurtosis of the models’ simulated Niño-3 index reveal that the quadratic model reproduces better the observed asymmetry between the positive El Niño and negative La Niña events. The benefits of the quadratic model are less clear in terms of its overall, cross-validated hindcast skill; this model outperforms, however, the linear one in predicting the magnitude of extreme SST anomalies. Seasonal ENSO dependence is captured by incorporating additive, as well as multiplicative forcing with a 12-month period into the first level of each model. The quasi-quadrennial ENSO oscillatory mode is robustly simulated by all models. The “spring barrier” of ENSO forecast skill is explained by Floquet and singular vector analysis, which show that the leading ENSO mode becomes strongly damped in summer, while nonnormal optimum growth has a strong peak in December.

scholarly journals Improving statistical prediction and revealing nonlinearity of ENSO using observations of ocean heat content in the tropical Pacific

2021 ◽  
Author(s):  
Aleksei Seleznev ◽  
Dmitry Mukhin
Keyword(s):  
Southern Oscillation ◽  
Nonlinear Models ◽  
Heat Content ◽  
Optimization Method ◽  
Tropical Pacific ◽  
Ocean Heat Content ◽  
Bayesian Optimization ◽  
Statistical Prediction ◽  
Seasonal Predictability ◽  
The Tropical Pacific

Abstract It is well-known that the upper ocean heat content (OHC) variability in the tropical Pacific contains valuable information about dynamics of El Niño–Southern Oscillation (ENSO). Here we combine sea surface temperature (SST) and OHC indices derived from the gridded datasets to construct a phase space for data-driven ENSO models. Using a Bayesian optimization method, we construct linear as well as nonlinear models for these indices. We find that the joint SST-OHC optimal models yield significant benefits in predicting both the SST and OHC as compared with the separate SST or OHC models. It is shown that these models substantially reduces seasonal predictability barriers in each variable – the spring barrier in the SST index and the winter barrier in the OHC index. We also reveal the significant nonlinear relationships between the ENSO variables manifesting on interannual scales, which opens prospects for improving yearly ENSO forecasting.

scholarly journals An Empirical Seasonal Rainfall Forecasting Model for the Northeast Region of Brazil

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1613
Author(s):  
Rodrigo Lins da Rocha Júnior ◽  
David Duarte Cavalcante Pinto ◽  
Fabrício Daniel dos Santos Silva ◽  
Heliofábio Barros Gomes ◽  
Helber Barros Gomes ◽  
...  
Keyword(s):  
Time Series ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Northern Region ◽  
Empirical Orthogonal Functions ◽  
Rainfall Forecasting ◽  
Orthogonal Functions ◽  
Northeast Region ◽  
Teleconnection Patterns ◽  
The North

The Northeast region of Brazil (NEB) is characterized by large climate variability that causes extreme and long unseasonal wet and dry periods. Despite significant model developments to improve seasonal forecasting for the NEB, the achievement of a satisfactory accuracy often remains a challenge, and forecasting methods aimed at reducing uncertainties regarding future climate are needed. In this work, we implement and assess the performance of an empirical model (EmpM) based on a decomposition of historical data into dominant modes of precipitation and seasonal forecast applied to the NEB domain. We analyzed the model’s performance for the February-March-April quarter and compared its results with forecasts based on data from the North American Multi-model Ensemble (NMME) project for the same period. We found that the first three leading precipitation modes obtained by empirical orthogonal functions (EOF) explained most of the rainfall variability for the season of interest. Thereby, this study focuses on them for the forecast evaluations. A teleconnection analysis shows that most of the variability in precipitation comes from sea surface temperature (SST) anomalies in various areas of the Pacific and the tropical Atlantic. The modes exhibit different spatial patterns across the NEB, with the first being concentrated in the northern half of the region and presenting remarkable associations with the El Niño-Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM), both linked to the latitudinal migration of the intertropical convergence zone (ITCZ). As for the second mode, the correlations with oceanic regions and its loading pattern point to the influence of the incursion of frontal systems in the southern NEB. The time series of the third mode implies the influence of a lower frequency mode of variability, probably related to the Interdecadal Pacific Oscillation (IPO). The teleconnection patterns found in the analysis allowed for a reliable forecast of the time series of each mode, which, combined, result in the final rainfall prediction outputted by the model. Overall, the EmpM outperformed the post-processed NMME for most of the NEB, except for some areas along the northern region, where the NMME showed superiority.

scholarly journals A Pacific Centennial Oscillation Predicted by Coupled GCMs*

2012 ◽  
Vol 25 (17) ◽  
pp. 5943-5961 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Jason E. Smerdon ◽  
Richard Seager ◽  
Jesús Fidel González-Rouco
Keyword(s):  
Time Scale ◽  
General Circulation ◽  
Southern Oscillation ◽  
Heat Content ◽  
General Circulation Models ◽  
Wave Pattern ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Centennial Time Scale ◽  
The Tropical Pacific

Abstract Internal climate variability at the centennial time scale is investigated using long control integrations from three state-of-the-art global coupled general circulation models. In the absence of external forcing, all three models produce centennial variability in the mean zonal sea surface temperature (SST) and sea level pressure (SLP) gradients in the equatorial Pacific with counterparts in the extratropics. The centennial pattern in the tropical Pacific is dissimilar to that of the interannual El Niño–Southern Oscillation (ENSO), in that the most prominent expression in temperature is found beneath the surface of the western Pacific warm pool. Some global repercussions nevertheless are analogous, such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows. Centennial variability in western equatorial Pacific SST is a result of the strong asymmetry of interannual ocean heat content anomalies, while the eastern equatorial Pacific exhibits a lagged, Bjerknes-like response to temperature and convection in the west. The extratropical counterpart is shown to be a flux-driven response to the hemispherically symmetric circulation anomalies emanating from the tropical Pacific. Significant centennial-length trends in the zonal SST and SLP gradients rivaling those estimated from observations and model simulations forced with increasing CO2 appear to be inherent features of the internal climate dynamics simulated by all three models. Unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties, beyond more traditional signal-to-noise estimates that do not account for natural variability on the centennial time scale.

scholarly journals Observed Ocean Variability in the Mindanao Dome Region

2011 ◽  
Vol 41 (2) ◽  
pp. 287-302 ◽  
Author(s):  
Yuji Kashino ◽  
Akio Ishida ◽  
Shigeki Hosoda
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Saline Water ◽  
Heat Content ◽  
Boreal Winter ◽  
Local Wind ◽  
Annual Variability ◽  
Mindanao Dome ◽  
Annual Signal

Abstract Ocean variations at semiannual, annual, and interannual time scales in the Mindanao Dome (MD) region of the southern Philippine Sea were examined using data derived from underwater sensors on Triangle Trans-Ocean Buoy Network (TRITON) buoys at 8°N, 137°E; 5°N, 137°E; and 8°N, 130°E. Annual signal dominated above 300-m depth in the MD region. At 5°N, 137°E, saline water exceeding 35 psu was observed at 100–200-m depth from boreal winter to spring, seemingly associated with the meridional migration of the North Equatorial Countercurrent during these seasons. Thermocline ascent, probably related to the MD, was also observed from boreal winter to spring. An important mechanism of the annual variation of the MD at 5°N seems to be the annual variability of local wind, as mentioned in past studies. However, annual variability at 8°N seems to be due to Rossby waves originating west of 150°W rather than to local wind effects. Semiannual variation was also observed, with its amplitude reaching 40%–70% of the annual signal. With regard to interannual variability, ocean variation on the time scale of the El Niño–Southern Oscillation (ENSO) was seen; upper heat content (above 300-m depth) in the Mindanao Dome region decreased during the 2002–03 and 2006–07 El Niño periods and increased between those periods. Increasing upper heat content in this region after 2005 was probably associated with large negative anomalies of Ekman pumping (downwelling) that appeared from 2005 to 2006 east of 150°E and north of 5°N.

scholarly journals Influence of Pacific Meridional Mode on ENSO evolution and predictability: Asymmetric modulation and ocean preconditioning

2020 ◽  
pp. 1-61
Author(s):  
Hanjie Fan ◽  
Bohua Huang ◽  
Song Yang ◽  
Wenjie Dong
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Enso Event ◽  
La Niña ◽  
Enso Events ◽  
La Nina ◽  
Meridional Mode ◽  
Pacific Meridional Mode

AbstractThis study investigates the mechanisms behind the Pacific Meridional Mode (PMM) in influencing the development of El Niño-Southern Oscillation (ENSO) event and its seasonal predictability. To examine the relative importance of various factors that may modulate the efficiency of the PMM influence, a series of experiments are conducted for selected ENSO events with different intensity using the Community Earth System Model, in which ensemble predictions are made from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. Overall, the matched PMM forcing to ENSO, i.e., a positive (negative) PMM prior to an El Niño (a La Niña), plays an enhancing role, while a mismatched PMM forcing plays a damping role. For the matched cases, a positive PMM event enhances an El Niño more strongly than a negative PMM event enhances a La Niña. This asymmetry in influencing ENSO largely originates from the asymmetry in intensity between the positive and negative PMM events in the tropics, which can be explained by the nonlinearity in the growth and equatorward propagation of the PMM-related anomalies of sea surface temperature (SST) and surface zonal wind through both wind-evaporation-SST feedback and summer deep convection response. Our model results also indicate that the PMM acts as a modulator rather than a trigger for the occurrence of ENSO event. Furthermore, the response of ENSO to an imposed PMM forcing is modulated by the preconditioning of the upper-ocean heat content, which provides the memory for the coupled low-frequency evolution in the tropical Pacific.

On associating significance levels with temporal changes in empirical orthogonal function analysis: a case study for ENSO

2020 ◽  
Author(s):  
Gabor Drotos
Keyword(s):  
Upper Bound ◽  
Null Hypothesis ◽  
Southern Oscillation ◽  
Function Analysis ◽  
Finite Size ◽  
Temporal Changes ◽  
Empirical Orthogonal Functions ◽  
Max Planck ◽  
Orthogonal Functions ◽  
Significance Level

<p>The availability of a large ensemble enables one to evaluate empirical orthogonal functions (EOFs) with respect to the ensemble without relying on temporal variability at all. Variability across the ensemble at any given time is supposed to represent the most relevant probability distribution for climate-related studies, and this distribution is presumably subject to temporal changes in the presence of time-dependent forcing. Such changes may be observable in spatial patterns of ensemble-based EOFs and associated eigenvalues. Unfortunately, estimates of these changes come with a considerable error due to the finite size of the ensemble, so that associating a significance level with the presence of a change (with respect to a null hypothesis about the absence of any change) should be the first step of analyzing the time evolution.</p><p>It turns out, however, that the conditions for the applicability of usual hypothesis tests about stationarity are not satisfied for the above-mentioned quantities. What proves to be feasible is to estimate an upper bound on the significance level for nonstationarity. This means that the true significance level would ideally be lower or equal to what is estimated, which would prevent unjustified confidence in the detection of nonstationarity (i.e., falsely rejecting the null hypothesis could not become more probable than claimed). Most importantly, one would avoid seriously overconfident conclusions about the sign of the change in this way. Notwithstanding, the estimate for the upper bound on the significance level is also affected by the finite number of the ensemble members. It nevertheless becomes more and more precise for increasing ensemble size and may serve as a first guidance for currently available ensemble sizes.</p><p>The details of the estimation are presented in the example of the EOF-based analysis of the El Niño–Southern Oscillation (ENSO) as it appears in the historical and RCP8.5 simulations of the Max Planck Institute Grand Ensemble. A comparison between results including and excluding ensemble members initialized with an incomplete spinup in system components with a long time scale is also given.</p>

Different Modes of Variability over the Tasman Sea: Implications for Regional Climate*

2014 ◽  
Vol 27 (22) ◽  
pp. 8466-8486 ◽  
Author(s):  
Stefan Liess ◽  
Arjun Kumar ◽  
Peter K. Snyder ◽  
Jaya Kawale ◽  
Karsten Steinhaeuser ◽  
...  
Keyword(s):  
New Zealand ◽  
Surface Temperature ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Empirical Orthogonal Functions ◽  
Seasonal Temperature ◽  
Orthogonal Functions ◽  
Tasman Sea ◽  
Eastern Australia ◽  
Precipitation Anomalies

Abstract A new approach is used to detect atmospheric teleconnections without being bound by orthogonality (such as empirical orthogonal functions). This method employs negative correlations in a global dataset to detect potential teleconnections. One teleconnection occurs between the Tasman Sea and the Southern Ocean. It is related to El Niño–Southern Oscillation (ENSO), the Indian Ocean dipole (IOD), and the southern annular mode (SAM). This teleconnection is significantly correlated with SAM during austral summer, fall, and winter, with IOD during spring, and with ENSO in summer. It can thus be described as a hybrid between these modes. Given previously found relationships between IOD and ENSO, and IOD’s proximity to the teleconnection centers, correlations to IOD are generally stronger than to ENSO. Increasing pressure over the Tasman Sea leads to higher (lower) surface temperature over eastern Australia (the southwestern Pacific) in all seasons and is related to reduced surface temperature over Wilkes Land and Adélie Land in Antarctica during fall and winter. Precipitation responses are generally negative over New Zealand. For one standard deviation of the teleconnection index, precipitation anomalies are positive over Australia in fall, negative over southern Australia in winter and spring, and negative over eastern Australia in summer. When doubling the threshold, the size of the anomalous high-pressure center increases and annual precipitation anomalies are negative over southeastern Australia and northern New Zealand. Eliassen–Palm fluxes quantify the seasonal dependence of SAM, ENSO, and IOD influences. Analysis of the dynamical interactions between these teleconnection patterns can improve prediction of seasonal temperature and precipitation patterns in Australia and New Zealand.

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