scholarly journals A waveform skewness index for measuring time series nonlinearity and its applications to the ENSO–Indian monsoon relationship

2022 ◽  
Vol 29 (1) ◽  
pp. 1-15
Author(s):  
Justin Schulte ◽  
Frederick Policelli ◽  
Benjamin Zaitchik
Keyword(s):  
Time Series ◽  
El Niño ◽  
Indian Monsoon ◽  
El Nino ◽  
Southern Oscillation ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Nonlinear Character ◽  
Indian Rainfall ◽  
Time Periods

Abstract. Many geophysical time series possess nonlinear characteristics that reflect the underlying physics of the phenomena the time series describe. The nonlinear character of times series can change with time, so it is important to quantify time series nonlinearity without assuming stationarity. A common way of quantifying the time evolution of time series nonlinearity is to compute sliding skewness time series, but it is shown here that such an approach can be misleading when time series contain periodicities. To remedy this deficiency of skewness, a new waveform skewness index is proposed for quantifying local nonlinearities embedded in time series. A waveform skewness spectrum is proposed for determining the frequency components that are contributing to time series waveform skewness. The new methods are applied to the El Niño–Southern Oscillation (ENSO) and the Indian monsoon to test a recently proposed hypothesis that states that changes in the ENSO–Indian monsoon relationship are related to ENSO nonlinearity. We show that the ENSO–Indian rainfall relationship weakens during time periods of high ENSO waveform skewness. The results from two different analyses suggest that the breakdown of the ENSO–Indian monsoon relationship during time periods of high ENSO waveform skewness is related to the more frequent occurrence of strong central Pacific El Niño events, supporting arguments that changes in the ENSO–Indian rainfall relationship are not solely related to noise.

scholarly journals A Waveform Skewness Index for Measuring Time Series Nonlinearity and its Applications to the ENSO-Indian Monsoon Relationship

2020 ◽  
Author(s):  
Justin Schulte ◽  
Frederick Policelli ◽  
Benjamin Zaitchik
Keyword(s):  
Time Series ◽  
El Niño ◽  
Indian Monsoon ◽  
El Nino ◽  
Southern Oscillation ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Nonlinear Character ◽  
Indian Rainfall ◽  
Time Periods

Abstract. Many geophysical time series possess nonlinear characteristics that reflect the underlying physics of the phenomena the time series describe. The nonlinear character of times series can change with time, so it is important to quantify time series nonlinearity without assuming stationarity. A common way to quantify the time-evolution of time series nonlinearity is to compute sliding skewness time series, but it is shown here that such an approach can be misleading when time series contain periodicities. To remedy this deficiency of skewness, a new waveform skewness index is proposed for quantifying local nonlinearities embedded in time series. A waveform skewness spectrum is proposed for determining the frequency components that are contributing to time series waveform skewness. The new methods are applied to the El Niño/ Southern Oscillation (ENSO) and the Indian monsoon to test a recently proposed hypothesis that states that changes in the ENSO-Indian Monsson relationship are related to ENSO nonlinearity. We show that the ENSO-Indian rainfall relationship weakens during time periods of high ENSO waveform skewness. The results from two different analyses suggest that the breakdown of the ENSO-Indian monsoon relationship during time periods of high ENSO waveform skewness is related to the more frequent occurrence of strong central Pacific El Niño events, supporting arguments that changes in the ENSO-Indian rainfall relationship are not solely related to noise.

scholarly journals A Skewed perspective of the Indian rainfall-ENSO Relationship

2019 ◽  
Author(s):  
Justin Schulte ◽  
Fredrick Policielli ◽  
Benjamin Zaitchik
Keyword(s):  
Time Series ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wavelet Coherence ◽  
Drought Severity ◽  
Nonlinear Phenomenon ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Highly Nonlinear

Abstract. The application of higher-order wavelet analysis to India rainfall and the El Niño/Southern Oscillation (ENSO) is presented. An auto-bicoherence analysis is used to extract the frequency modes contributing to the skewness of India rainfall and ENSO. A nonlinear wavelet coherence method is proposed for diagnosing why the time-domain correlation between two time series temporally changes when at least one time series has changing nonlinear characteristics. The results indicate the India rainfall and ENSO are highly nonlinear phenomenon. It is also demonstrated that the sea surface temperature (SST) patterns associated with different nonlinear ENSO modes depend on the frequency components participating in the nonlinear phase coupling. The SST pattern associated with coupling between ENSO modes with periods of 31 and 15.5 months is reminiscent of a central Pacific El Niño and intensifies around 1995, contrasting with the coupling between the 62- and 31-month modes that became active around the 1970s ENSO regime shift. A nonlinear coherence analysis showed that the skewness of India rainfall is weakly correlated with that of 4 ENSO time series after the 1970s, indicating that increases in ENSO skewness after 1970's at least partially contributed to the weakening India rainfall-ENSO relationship in recent decades. The implication of this result is that the intensity of skewed El Niño events is likely to overestimate India drought severity, which was the case in the 1997 monsoon season, a time point when the nonlinear wavelet coherence between All-India rainfall and ENSO reached its lowest value in the 1871–2016 period.

scholarly journals ENSO flavors in a tree-ring δ<sup>18</sup>O record of <i>Tectona grandis</i> from Indonesia

2015 ◽  
Vol 11 (10) ◽  
pp. 1325-1333 ◽  
Author(s):  
K. Schollaen ◽  
C. Karamperidou ◽  
P. Krusic ◽  
E. Cook ◽  
G. Helle
Keyword(s):  
Tree Ring ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Enso Events ◽  
Proxy Records ◽  
El Niño Events ◽  
El Nino Events

Abstract. Indonesia's climate is dominated by the equatorial monsoon system, and has been linked to El Niño-Southern Oscillation (ENSO) events that often result in extensive droughts and floods over the Indonesian archipelago. In this study we investigate ENSO-related signals in a tree-ring δ18O record (1900–2007) of Javanese teak. Our results reveal a clear influence of Warm Pool (central Pacific) El Niño events on Javanese tree-ring δ18O, and no clear signal of Cold Tongue (eastern Pacific) El Niño events. These results are consistent with the distinct impacts of the two ENSO flavors on Javanese precipitation, and illustrate the importance of considering ENSO flavors when interpreting palaeoclimate proxy records in the tropics, as well as the potential of palaeoclimate proxy records from appropriately selected tropical regions for reconstructing past variability of. ENSO flavors.

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 Three-Region Conceptual Model for Central Pacific El Niño Including Zonal Advective Feedback

2018 ◽  
Vol 31 (13) ◽  
pp. 4965-4979 ◽  
Author(s):  
Xiang-Hui Fang ◽  
Mu Mu
Keyword(s):  
Surface Temperature ◽  
Conceptual Model ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Eastern Equatorial Pacific

The simple zonal two-region framework of the recharge paradigm can accurately manifest the traditional eastern Pacific (EP) type of El Niño–Southern Oscillation (ENSO), as its major warming center is located in the EP and the anomalous sea surface temperature (SST) changes monotonically from west to east along the equatorial Pacific. However, it cannot fully depict the variations of the central Pacific (CP) type of ENSO, whose major warming center is mainly situated in the CP. Therefore, to better investigate the characteristics of the CP type of ENSO, the recharge paradigm is extended to a three-region conceptual model to describe the entire western, central, and eastern equatorial Pacific. The results show that the extended conceptual model can depict the different variations between the CP and EP well. Specifically, with increasing magnitude of the zonal advective feedback over the CP (i.e., imitating the situation for CP ENSO), the period of the system and SST magnitude over the CP and EP both decrease. However, the decreasing amplitude is more intense over the EP, indicating an enlargement of the SST differences between the CP and EP. These results are all consistent with the observational characteristics of CP ENSO.

scholarly journals Interannual and Decadal Variability in Tropical Pacific Chlorophyll from a Statistical Reconstruction: 1958–2008

2017 ◽  
Vol 30 (18) ◽  
pp. 7293-7315 ◽  
Author(s):  
Stephanie Schollaert Uz ◽  
Antonio J. Busalacchi ◽  
Thomas M. Smith ◽  
Michael N. Evans ◽  
Christopher W. Brown ◽  
...  
Keyword(s):  
El Niño ◽  
Decadal Variability ◽  
El Nino ◽  
Southern Oscillation ◽  
Ocean Color ◽  
Sea Surface ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Equatorial Undercurrent ◽  
Statistical Reconstruction

Abstract Historical understanding of marine biological dynamics has been limited by sparse in situ observations and the fact that dedicated ocean color satellite remote sensing only began in 1997. From these observations, it has become clear that physical oceanography controls biological variability over seasonal to interannual time scales. To quantify how multidecadal, climate-scale patterns impact biological productivity, the strong correlation with sea surface temperature and sea surface height is utilized to reconstruct a retrospective 51-yr time series of surface chlorophyll, the pigment measured by ocean color satellites. The canonical correlation analysis statistical reconstruction demonstrates greatest skill away from land and within about 10° of the equator where chlorophyll variance is greatest and predominantly associated with El Niño–Southern Oscillation dynamics. Differences in chlorophyll patterns between east or central Pacific El Niño events are observed, with larger declines east of 180° for east Pacific events and west of 180° for central Pacific events. Additionally, small but significant decadal variations in chlorophyll patterns are observed corresponding to the Pacific decadal oscillation. Decadal changes in chlorophyll west of 180° are consistent with increased stratification, whereas changes between 110°–140°W may be related to long-term shoaling of the nutrient-bearing equatorial undercurrent.

scholarly journals ENSO flavors in a tree-ring δ<sup>18</sup>O record of <i>Tectona grandis</i> from Indonesia

2014 ◽  
Vol 10 (5) ◽  
pp. 3965-3987 ◽  
Author(s):  
K. Schollaen ◽  
C. Karamperidou ◽  
P. J. Krusic ◽  
E. R. Cook ◽  
G. Helle
Keyword(s):  
Tree Ring ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tectona Grandis ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Enso Events ◽  
El Niño Events ◽  
El Nino Events

Abstract. Indonesia's climate is dominated by the equatorial monsoon system, and has been linked to El Niño–Southern Oscillation (ENSO) events that often result in extensive droughts and floods over the Indonesian archipelago. In this study we investigate ENSO-related signals in a tree-ring δ18O record (1900–2007) of Javanese teak. Our results reveal a clear influence of Warm Pool (central Pacific) El Niño events on Javanese tree-ring δ18O, and no clear signal of Cold Tongue (eastern Pacific) El Niño events. These results are consistent with the distinct impacts of the two ENSO flavors on Javanese precipitation, and illustrate the importance of considering ENSO flavors when interpreting palaeoclimate proxy records in the tropics.

scholarly journals Seasonal Synchronization of a Simple Stochastic Dynamical Model Capturing El Niño Diversity

2017 ◽  
Vol 30 (24) ◽  
pp. 10047-10066 ◽  
Author(s):  
Sulian Thual ◽  
Andrew Majda ◽  
Nan Chen
Keyword(s):  
El Niño ◽  
Cloud Cover ◽  
El Nino ◽  
Southern Oscillation ◽  
Eastern Pacific ◽  
Dynamical Model ◽  
Boreal Winter ◽  
Convective Activity ◽  
Central Pacific ◽  
Central Pacific El Niño

Recently, a simple stochastic dynamical model was developed that automatically captures the diversity and intermittency of El Niño–Southern Oscillation (ENSO) in nature, where state-dependent stochastic wind bursts and nonlinear advection of sea surface temperature (SST) are coupled to simple ocean–atmosphere processes that are otherwise deterministic, linear, and stable. In the present article, it is further shown that the model can reproduce qualitatively the ENSO synchronization (or phase locking) to the seasonal cycle in nature. This goal is achieved by incorporating a cloud radiative feedback that is derived naturally from the model’s atmosphere dynamics with no ad hoc assumptions and accounts in simple fashion for the marked seasonal variations of convective activity and cloud cover in the eastern Pacific. In particular, the weak convective response to SSTs in boreal fall favors the eastern Pacific warming that triggers El Niño events while the increased convective activity and cloud cover during the following spring contributes to the shutdown of those events by blocking incoming shortwave solar radiations. In addition to simulating the ENSO diversity with realistic non-Gaussian statistics in different Niño regions, the eastern Pacific moderate and super El Niño and the central Pacific El Niño and La Niña show a realistic chronology with a tendency to peak in boreal winter as well as decreased predictability in spring consistent with the persistence barrier in nature. The incorporation of other possible seasonal feedbacks in the model is also documented for completeness.

scholarly journals Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Guojian Wang ◽  
Wenju Cai
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Greenhouse Warming ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Positive Indian Ocean Dipole ◽  
The Future ◽  
Rainfall Anomalies

Abstract The 2019/20 Australian black summer bushfires were particularly severe in many respects, including its early commencement, large spatial coverage, and large number of burning days, preceded by record dry and hot anomalies. Determining whether greenhouse warming has played a role is an important issue. Here, we examine known modes of tropical climate variability that contribute to droughts in Australia to provide a gauge. We find that a two-year consecutive concurrence of the 2018 and 2019 positive Indian Ocean Dipole and the 2018 and 2019 Central Pacific El Niño, with the former affecting Southeast Australia, and the latter influencing eastern and northeastern Australia, may explain many characteristics of the fires. Such consecutive events occurred only once in the observations since 1911. Using two generations of state-of-the-art climate models under historical and a business-as-usual emission scenario, we show that the frequency of such consecutive concurrences increases slightly, but rainfall anomalies during such events are stronger in the future climate, and there are drying trends across Australia. The impact of the stronger rainfall anomalies during such events under drying trends is likely to be exacerbated by greenhouse warming-induced rise in temperatures, making such events in the future even more extreme.

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