Orthogonal PDO and ENSO Indices

2016 ◽  
Vol 29 (10) ◽  
pp. 3883-3892 ◽  
Author(s):  
Xianyao Chen ◽  
John M. Wallace
Keyword(s):  
Decadal Variability ◽  
Spatial Regression ◽  
Power Spectra ◽  
Enso Cycle ◽  
Orthogonal Axis ◽  
Sst Variability ◽  
Dimensional Phase Space ◽  
Highly Correlated ◽  
The Time Domain ◽  
Enso Indices

Abstract A framework for interpreting the Pacific decadal oscillation (PDO) and ENSO indices is presented. The two leading principal components (PCs) of sea surface temperature [SST; strictly speaking, the departure from globally averaged SST (SST*)] over the entire Pacific basin comprise a two-dimensional phase space. A linear combination of these pan-Pacific PCs corresponding to a +45° rotation (designated by P) is nearly identical to the PDO, the leading PC of Pacific SST* poleward of 20°N. Both P and the PDO index exhibit apparent “regime shifts” on the interdecadal time scale. The orthogonal axis (rotated by −45° and designated by T′) is highly correlated with conventional ENSO indices, but its spatial regression pattern is more equatorially focused. SST variability along these two rotated axes exhibits sharply contrasting power spectra, the former (i.e., P) suggestive of “red noise” on time scales longer than a decade and the latter (i.e., T′) exhibiting a prominent spectral peak around 3–5 years. Hence, orthogonal indices representative of the ENSO cycle and ENSO-like decadal variability can be generated without resorting to filtering in the time domain. The methodology used here is the same as that used by Takahashi et al. to quantify the diversity of equatorial SST patterns in ENSO; they rotated the two leading EOFs of tropical Pacific SST, whereas the two leading EOFs of pan-Pacific SST* are rotated here.

ENSO-Like Variability: 1900–2013*

2015 ◽  
Vol 28 (24) ◽  
pp. 9623-9641 ◽  
Author(s):  
Xianyao Chen ◽  
John M. Wallace
Keyword(s):  
Sea Level ◽  
Spatial Regression ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Late Nineteenth Century ◽  
Enso Cycle ◽  
Mode Decomposition ◽  
The Pacific ◽  
Background Continuum ◽  
Highly Correlated

Abstract ENSO-like variability is examined using a set of univariate indices based on unfiltered monthly global sea surface temperature (SST), sea level pressure (SLP), outgoing longwave radiation (OLR), sea level, and the three-dimensional ocean temperature (OT) fields. These indices, many of which correspond to the leading principal components (PCs) of the respective global fields, are highly correlated with each other. In combination with their spatial regression patterns, they provide a comprehensive description of ENSO-like variability in the atmosphere and ocean across time scales ranging from months to decades, from 1950 onward. The SLP and SST indices are highly correlated with one another back to the late nineteenth century. The interdecadal-scale shifts in the prevailing polarity of ENSO that occurred in the 1940s, the 1970s, and around the year 2000 are clearly evident in low-pass-filtered time series of these indices. On the basis of empirical mode decomposition, ENSO-like variability is partitioned into an interannual “ENSO cycle,” to which equatorial ocean wave dynamics imparts a distinctive equatorial signature, and a red noise background continuum, most prominent on the interdecadal time scale, which resembles the ENSO-like variability in some models in which the atmosphere is coupled to a slab ocean. The background continuum bears the imprint of the Pacific–North American (PNA) pattern, the leading mode of the Northern Hemisphere wintertime variability of the atmospheric circulation over the Pacific sector. The superposition of the ENSO cycle and the background continuum imparts a distinctive frequency dependence to the patterns of ENSO-like climate variability.

scholarly journals Random time series in astronomy

2013 ◽  
Vol 371 (1984) ◽  
pp. 20110549 ◽  
Author(s):  
Simon Vaughan
Keyword(s):  
Time Series ◽  
Black Holes ◽  
Time Domain ◽  
Gamma Ray ◽  
Power Spectra ◽  
Polarization Angle ◽  
Noise Power ◽  
Future Challenges ◽  
Nearby Galaxies ◽  
The Time Domain

Progress in astronomy comes from interpreting the signals encoded in the light received from distant objects: the distribution of light over the sky (images), over photon wavelength (spectrum), over polarization angle and over time (usually called light curves by astronomers). In the time domain, we see transient events such as supernovae, gamma-ray bursts and other powerful explosions; we see periodic phenomena such as the orbits of planets around nearby stars, radio pulsars and pulsations of stars in nearby galaxies; and we see persistent aperiodic variations (‘noise’) from powerful systems such as accreting black holes. I review just a few of the recent and future challenges in the burgeoning area of time domain astrophysics, with particular attention to persistently variable sources, the recovery of reliable noise power spectra from sparsely sampled time series, higher order properties of accreting black holes, and time delays and correlations in multi-variate time series.

scholarly journals Clustering revisited: A spectral analysis of microseismic events

Geophysics ◽  
2013 ◽  
Vol 78 (2) ◽  
pp. KS41-KS49 ◽  
Author(s):  
Deborah Fagan ◽  
Kasper van Wijk ◽  
James Rutledge
Keyword(s):  
Oil Recovery ◽  
Time Domain ◽  
Power Spectra ◽  
Fault System ◽  
Microseismic Events ◽  
The Fourier Transform ◽  
The Time Domain ◽  
The Relationship ◽  
Single Cluster ◽  
Full Body

Identifying individual subsurface faults in a larger fault system is important to characterize and understand the relationship between microseismicity and subsurface processes. This information can potentially help drive reservoir management and mitigate the risks of natural or induced seismicity. We have evaluated a method of statistically clustering power spectra from microseismic events associated with an enhanced oil recovery operation in southeast Utah. Specifically, we were able to provide a clear distinction within a set of events originally designated in the time domain as a single cluster and to identify evidence of en echelon faulting. Subtle time-domain differences between events were accentuated in the frequency domain. Power spectra based on the Fourier transform of the time-domain autocorrelation function were used, as this formulation results in statistically independent intensities and is supported by a full body of statistical theory upon which decision frameworks can be developed.

North Atlantic SST variability and high impact storms affecting the Iberian Peninsula

2020 ◽  
Author(s):  
Fátima Ferreira ◽  
Margarida L. R. Liberato ◽  
Alexandre M. Ramos ◽  
Raquel Nieto
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Decadal Variability ◽  
High Impact ◽  
Average Intensity ◽  
Weather Extremes ◽  
The North ◽  
Sst Variability ◽  
Extreme Precipitation Events ◽  
The North Atlantic

<p>The Iberian Peninsula has experienced on recent years an increasing number of high impact cyclones (e.g. Klaus, 23-24 January 2009 and Xynthia, 27-28 February 2010; Liberato et al. 2011; 2013) associated with extreme precipitation events, flooding and damage to infrastructure. Recent examples are cyclones Elsa and Fabien, on December 2019, which forced more than 250 people to be evacuated from their homes in Mondego region villages, in central Portugal, due to rising river waters and infrastructure disruption .</p><p>However until now not enough evidence has been gathered to confirm a general and significant increase in the frequency and intensity of these events in the north-eastern Atlantic. In fact, according to Karremann et al. (2016) the maximum in recent years is comparable to other stormy periods in the 1960s and 1980s, suggesting that their frequency of occurrence undergoes strong multi-decadal variability.</p><p>In this study a high impact extratropical cyclones dataset developed in the framework of project “WEx-Atlantic - Weather Extremes in the Euro Atlantic Region: Assessment and Impacts” is used to assess the variability in frequency and intensity of these events over the last decades in the Iberian Peninsula. A ranking of daily precipitation days for the Iberian Peninsula taking into account not only the area affected but also its average intensity (Ramos et al. 2014) is also used. Additionally, a spatio-temporal variability of sea surface temperature (SST) is performed in the North Atlantic, using ECMWF ERA5 reanalysis data for the period 1979-2019. Finally the relevance of the North Atlantic SST variability on the intensity of these extreme events affecting the Iberian Peninsula on recent winter seasons is discussed.  </p><p><strong>Acknowledgements</strong></p><p>The authors would like to acknowledge the financial support by Fundação para a Ciência e a Tecnologia, Portugal (FCT), through projects PTDC/CTA-MET/29233/2017 and UIDB/50019/2020 – IDL. A.M. Ramos is supported by Scientific Employment Stimulus 2017 from FCT (CEECIND/00027/2017).</p><p><strong>References</strong></p><p>Karremann et al. (2016) Atmos. Sci. Let., 17: 354-361 DOI: 10.1002/asl.665</p><p>Liberato et al. (2011) Weather, 66: 330-334 DOI: 10.1002/wea.755</p><p>Liberato et al. (2013) Nat. Hazards Earth Syst. Sci., 13: 2239-2251 DOI: 10.5194/nhess-13-2239-2013</p><p>Ramos et al. (2014) Atmos. Sci. Let., 15: 328–334, DOI: 10.1002/asl2.507</p>

Automatic assessment of electromyogram quality

1995 ◽  
Vol 79 (5) ◽  
pp. 1803-1815 ◽  
Author(s):  
C. Sinderby ◽  
L. Lindstrom ◽  
A. E. Grassino
Keyword(s):  
Gastroesophageal Junction ◽  
Power Spectra ◽  
Center Frequency ◽  
High Signal ◽  
Computer Algorithms ◽  
Automatic Assessment ◽  
Intramuscular Electrodes ◽  
The Common ◽  
The Time Domain ◽  
Selection Of

Power spectrum analysis of the diaphragm electromyogram (EMGdi) is time consuming, and no criteria have been developed to objectively quantify contamination of the signal. The present work describes a set of computer algorithms that automatically select EMGdi free of the electrocardiogram and numerically quantify the common artifacts that affect the EMGdi. The algorithms were tested 1) on human EMGdi (n = 5) obtained with esophageal electrodes positioned at the level of the gastroesophageal junction, 2) on EMGdi obtained in mongrel dogs (n = 5) with intramuscular electrodes in the costal diaphragm, and 3) on computer-simulated power spectra. For authentic and simulated power spectra, indexes were obtained by the algorithms and were able to quantify signal disturbances induced by noise, electrode motion, esophageal peristalsis (in humans), and non-QRS complex-related electrocardiogram activity. With the index inclusion thresholds set to levels that allowed for a high signal acceptance rate with relatively small artifact-induced fluctuations (10–15%) of the EMGdi center frequency, the computer algorithms were found to be as reliable as or more reliable than other methods, including careful visual selection of the time domain signals by experienced analysts. In conclusion, the frequency domain application of computer algorithms offers a reliable and reproducible means to objectively quantify the sources that contaminate the interference pattern EMG.

scholarly journals The Contribution of the Interannual ENSO Cycle to the Spatial Pattern of Decadal ENSO-Like Variability*

2005 ◽  
Vol 18 (12) ◽  
pp. 2080-2092 ◽  
Author(s):  
Daniel J. Vimont
Keyword(s):  
Spatial Structure ◽  
Spatial Information ◽  
Decadal Variability ◽  
Enso Event ◽  
Enso Cycle ◽  
Physical Explanation ◽  
Enso Variability ◽  
Physical Mechanisms ◽  
Spatial Features

Abstract A defining feature of Pacific decadal ENSO-like variability is the similarity between its spatial expression in sea surface temperature (SST) and the spatial structure of interannual ENSO variability. This similarity may indicate that the decadal variability is merely a long-term average over interannual ENSO variability. In contrast, subtle differences (namely the meridionally broadened tropical SST signature and emphasized midlatitude SST anomalies for the decadal ENSO-like pattern) may indicate that fundamentally different processes are responsible for generating variability on the decadal to interdecadal time scale. The present study attempts to reconcile the subtly different spatial structures of interannual ENSO and decadal ENSO-like variability by relating the decadal pattern to various SST patterns associated with the development of the interannual ENSO cycle. First, a statistical analysis is used to reconstruct the decadal ENSO-like SST pattern as a linear combination of interannual SST patterns. It is shown that the decadal ENSO-like pattern is well reconstructed in the absence of decadal spatial information. Next, these interannual patterns are physically interpreted in relation to the interannual ENSO cycle. The analysis reveals that the decadal ENSO-like SST pattern is obtained by averaging over three SST patterns associated with ENSO precursors, the peak of an ENSO event, and ENSO “leftovers.” The study provides a plausible physical explanation for the spatial structure of ENSO-like decadal variability as an average over variations in the interannual ENSO cycle. The results indicate that the prominent spatial features of decadal ENSO-like variability are generated by physical mechanisms that operate through the interannual ENSO cycle. This does not imply, however, that decadal processes are unimportant in altering the decadal properties of ENSO. Results may provide a framework for interpreting modeled decadal ENSO-like variability and for constraining plausible mechanisms of tropical decadal variability.

scholarly journals Factors Associated with Decadal Variability in Great Plains Summertime Surface Temperatures

2013 ◽  
Vol 26 (1) ◽  
pp. 343-350 ◽  
Author(s):  
Scott J. Weaver
Keyword(s):  
Surface Temperature ◽  
Great Plains ◽  
Decadal Variability ◽  
Atlantic Multidecadal Oscillation ◽  
Regional Warming ◽  
Factors Associated ◽  
Sst Variability ◽  
The Pacific ◽  
Low Level Jet ◽  
Decadal Climate

Abstract Decadal variability of summertime Great Plains surface temperature is probed from the perspective of the Great Plains low-level jet (GPLLJ). GPLLJ variability modes 2 and 5 are shown to be most influential on the evolution and magnitude of Great Plains surface temperature anomalies over the latter half of the twentieth century, including the development of the summertime warming hole and are further linked to the Pacific decadal oscillation (PDO) and Atlantic multidecadal oscillation (AMO), respectively. The connection between GPLLJ variability and Great Plains surface temperature is strongest when the PDO and AMO are oppositely phased, and in the case of the warming hole, a preference for a positive (negative) PDO (AMO). The influence of remote SST variability on the central U.S. warming hole is broadly consistent with previous modeling studies. However, the pivotal role that GPLLJ variability plays in linking the hemispheric-wide SST variability (through the AMO and PDO) to the regional warming hole is an expanded and clarified perspective. These findings unify the results of recent studies from the U.S. Climate Variability and Predictability (CLIVAR) Drought Working Group and have implications for decadal climate prediction efforts.

Observed and simulated (CMIP5 and CMIP6) early- to late-winter evolution of North Atlantic atmospheric variability and links to the ocean

2020 ◽  
Author(s):  
Thomas Bracegirdle
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Climate Models ◽  
Decadal Variability ◽  
Low Frequency ◽  
Late Winter ◽  
Atmospheric Variability ◽  
Sst Variability ◽  
Early Results ◽  
Depth Analysis

<p>Research to date has shown strong multi-decadal variability of the North Atlantic Oscillation (NAO) in late winter, particularly in March when correlations to North Atlantic (NA) ocean variability (Atlantic multi-decadal variability (AMV)) are particularly strong. This late-winter low-frequency atmospheric variability appears too weak in the majority of climate models across a range of indices of North Atlantic large-scale atmospheric circulation. It appears that models do not successfully reproduce responses to either (or both) proximal sea-surface temperature (SST) variability at mid-latitudes or teleconnections to SST variability in the sub tropics. </p><p>Here, an in-depth analysis of the winter evolution of multiple indices of North Atlantic mid-latitude atmospheric circulation will be presented based on both re-analysis data and historical simulations of coupled climate models (CMIP5 and CMIP6). The atmospheric indices assessed will include the NAO, speed and latitude of the NA eddy driven jet and lower-tropospheric westerly wind strength in a region of maximum variability to the west of the UK. Results so far indicate that the CMIP6 models do not exhibit a clear change from CMIP5 in terms of the representation of low-frequency late-winter atmospheric variability. To diagnose in more detail possible origins of differences between observed and simulated variability, a detailed evaluation of early- to late-winter evolution in variability of the above indices will be presented, with an initial focus on observations (re-analysis and SST re-constructions) and incorporating the following questions:  <br>- Are there significant differences in the relative strength of linkages to tropical and extra-tropical SST variability across the different atmospheric indices? <br>- Is the observed late-winter maximum in correlations between NA atmospheric indices and North Atlantic SSTs still apparent at sub-decadal timescales?<br>Initial results indicate that there are stronger tropical linkages for jet speed and that at sub-decadal timescales late winter is does not dominate in terms of correlations between atmospheric and SST variability. Updates on these early results will be presented along with implications of the results for differences between observed and simulated variability. </p>

scholarly journals Implications of Both Statistical Equilibrium and Global Warming Simulations with CCSM3. Part I: On the Decadal Variability in the North Pacific Basin

2009 ◽  
Vol 22 (20) ◽  
pp. 5277-5297 ◽  
Author(s):  
Marc d’Orgeville ◽  
W. Richard Peltier
Keyword(s):  
Global Warming ◽  
North Pacific ◽  
Time Scale ◽  
Decadal Variability ◽  
Sea Surface ◽  
The North ◽  
Sst Variability ◽  
Pacific Decadal Variability ◽  
The North Pacific ◽  
North Pacific Basin

Abstract In the low-resolution version of the Community Climate System Model, version 3 (CCSM3), the modeled North Pacific decadal variability is demonstrated to be independent of the epoch for which a statistically steady control simulation is constructed, either preindustrial or modern; however, it is demonstrated to be significantly affected by the different global warming scenarios investigated. In the control simulations, the North Pacific basin is shown to be dominated by sea surface temperature (SST) variability with a time scale of approximately 20 yr. This mode of variability is in close accord with the observed characteristics of the Pacific decadal oscillation (PDO). A detailed analysis of the statistical equilibrium runs is performed based on other model variables as well [sea surface salinity (SSS), barotropic circulation, freshwater and heat fluxes, wind stress curl, sea ice, and snow coverage]. These analyses confirm that the underlying mechanism of the PDO involves a basin-scale mode of ocean adjustment to changes of the atmospheric forcing associated with the Aleutian low pressure system. However, they also suggest that the observed sign reversal of the PDO arises from a feedback in the northern part of the basin. In this novel hypothesis, the advection to the Bering Sea of “spice” anomalies formed in the central and western Pacific sets up a typical 10-yr time scale for the triggering of the PDO reversal. In all of the global warming simulations described in this paper, the signal represented by the detrended SST variability in the North Pacific displays significant power at multidecadal frequencies. In these simulations, the natural North Pacific decadal variability, as characterized in the control simulations (the PDO), remains the leading mode of variability only for moderate forcing. If the warming is too strong, then the typical 20-yr time scale of the canonical PDO can no longer be detected, except in terms of SSS variability and only prior to a significant change that occurs in the Bering Strait Throughflow.

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