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Advanced Spectral Methods for Climatic Time Series
, 2001
"... The analysis of uni- or multivariate time series provides crucial information to describe, understand, and predict climatic variability. The discovery and implementation of a number of novel methods for extracting useful information from time series has recently revitalized this classical eld of ..."
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Cited by 220 (35 self)
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The analysis of uni- or multivariate time series provides crucial information to describe, understand, and predict climatic variability. The discovery and implementation of a number of novel methods for extracting useful information from time series has recently revitalized this classical eld of study. Considerable progress has also been made in interpreting the information so obtained in terms of dynamical systems theory.
Resonance in bidecadal and pentadecadal climate oscillations over the North Pacific: Role in climatic regime shifts, Geophys
- Res. Lett
, 1999
"... Abstract. The roles of interdecadal oscillations in cli-matic regime shifts, which are observed as rapid strength changes in the Aleutian low in winter and spring sea-sons, have been analyzed. A regime shift results from simultaneous phase reversals between pentadecadal and bidecadal variations, whi ..."
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Cited by 73 (5 self)
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Abstract. The roles of interdecadal oscillations in cli-matic regime shifts, which are observed as rapid strength changes in the Aleutian low in winter and spring sea-sons, have been analyzed. A regime shift results from simultaneous phase reversals between pentadecadal and bidecadal variations, which synchronize with one an-other at a relative period of three. The pentadecadal variation, which is observed in both winter and spring seasons, provides the basic timescale of regime shifts, while the bidecadal variation, which is observed only in winter, characterizes the rapidity of the shifts. A Monte-Carlo simulation has shown that the simultaneous phase reversals or resonance between the pentadecadal and bidecadal variations reflect a physical linkage between them and do not coincide accidentally. The role of this synchronization feature for assessing and predicting regime shifts is discussed.
A review of analytical techniques for gait data. Part 2: neural network and wavelet methods
- GAIT AND POSTURE
, 2001
"... Multivariate gait data have traditionally been challenging to analyze. Part 1 of this review explored applications of fuzzy, multivariate statistical and fractal methods to gait data analysis. Part 2 extends this critical review to the applications of artificial neural networks and wavelets to gait ..."
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Cited by 64 (0 self)
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Multivariate gait data have traditionally been challenging to analyze. Part 1 of this review explored applications of fuzzy, multivariate statistical and fractal methods to gait data analysis. Part 2 extends this critical review to the applications of artificial neural networks and wavelets to gait data analysis. The review concludes with a practical guide to the selection of alternative gait data analysis methods. Neural networks are found to be the most prevalent non-traditional methodology for gait data analysis in the last 10 years. Interpretation of multiple gait signal interactions and quantitative comparisons of gait waveforms are identified as important data analysis topics in need of further research.
Neural activity when people solve verbal problems with insight. PLoS Biology
- PLoS Biology
, 2004
"... People sometimes solve problems with a unique process called insight, accompanied by an ‘‘Aha!’ ’ experience. It has long been unclear whether different cognitive and neural processes lead to insight versus noninsight solutions, or if solutions differ only in subsequent subjective feeling. Recent be ..."
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Cited by 52 (3 self)
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People sometimes solve problems with a unique process called insight, accompanied by an ‘‘Aha!’ ’ experience. It has long been unclear whether different cognitive and neural processes lead to insight versus noninsight solutions, or if solutions differ only in subsequent subjective feeling. Recent behavioral studies indicate distinct patterns of performance and suggest differential hemispheric involvement for insight and noninsight solutions. Subjects solved verbal problems, and after each correct solution indicated whether they solved with or without insight. We observed two objective neural correlates of insight. Functional magnetic resonance imaging (Experiment 1) revealed increased activity in the right hemisphere anterior superior temporal gyrus for insight relative to noninsight solutions. The same region was active during initial solving efforts. Scalp electroencephalogram recordings (Experiment 2) revealed a sudden burst of high-frequency (gamma-band) neural activity in the same area beginning 0.3 s prior to insight solutions. This right anterior temporal area is associated with making connections across distantly related information during comprehension. Although all problem solving relies on a largely shared cortical network, the sudden flash of insight occurs when solvers engage distinct neural and cognitive processes that allow them to see connections that previously eluded them.
Stochastic forcing of ENSO by the intraseasonal oscillation
- Journal of Climate
, 1999
"... Using the ideas of generalized linear stability theory, the authors examine the potential role that tropical variability on synoptic–intraseasonal timescales can play in controlling variability on seasonal–interannual timescales. These ideas are investigated using an intermediate coupled ocean–atmos ..."
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Cited by 46 (0 self)
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Using the ideas of generalized linear stability theory, the authors examine the potential role that tropical variability on synoptic–intraseasonal timescales can play in controlling variability on seasonal–interannual timescales. These ideas are investigated using an intermediate coupled ocean–atmosphere model of the El Niño– Southern Oscillation (ENSO). The variability on synoptic–intraseasonal timescales is treated as stochastic noise that acts as a forcing function for variability at ENSO timescales. The spatial structure is computed that the stochastic noise forcing must have in order to enhance the variability of the system on seasonal–interannual timescales. These structures are the so-called stochastic optimals of the coupled system, and they bear a good resemblence to variability that is observed in the real atmosphere on synoptic and intraseasonal timescales. When the coupled model is subjected to a stochastic noise forcing composed of the stochastic optimals, variability on seasonal–interannual timescales develops that has spectral characteristics qualitatively similar to those seen in nature. The stochastic noise forcing produces perturbations in the system that can grow rapidly. The response of the system to the stochastic optimals is to induce perturbations that bear a strong resemblence to westerly and easterly wind bursts frequently observed in the western tropical Pacific. In the model, these ‘‘wind bursts’’ can act as efficient precursors for ENSO episodes if conditions are favorable. The response of the system to
A tree‐ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567
- 5of6 TING ET AL.: ROBUST AMV PATTERNS L17705
, 2004
"... [1] We present a tree-ring based reconstruction of the Atlantic Multidecadal Oscillation (AMO) which demonstrates that strong, low-frequency (60–100 yr) variability in basin-wide (0–70°N) sea surface temperatures (SSTs) has been a consistent feature of North Atlantic climate for the past five centur ..."
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Cited by 42 (0 self)
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[1] We present a tree-ring based reconstruction of the Atlantic Multidecadal Oscillation (AMO) which demonstrates that strong, low-frequency (60–100 yr) variability in basin-wide (0–70°N) sea surface temperatures (SSTs) has been a consistent feature of North Atlantic climate for the past five centuries. Intervention analysis of reconstructed AMO indicates that 20th century modes were similar to those in the preceding 350 yr, and wavelet spectra show robust multidecadal oscillations throughout the reconstruction. Though the exact relationships between low-frequency SST modes, higher frequency ( 7–25 yr) atmospheric modes (e.g., North Atlantic Oscillation/Arctic Oscillation), and terrestrial climates must still be resolved, our results confirm that the AMO should be considered in assessments of past and future Northern Hemisphere
Correlates of alpha rhythm in functional magnetic resonance imaging and near infrared spectroscopy
- Neuroimage
, 2003
"... We used simultaneous electroencephalogram-functional magnetic resonance imaging (EEG-fMRI) and EEG-near infrared spectroscopy (NIRS) to investigate whether changes of the posterior EEG alpha rhythm are correlated with changes in local cerebral blood oxygenation. Cross-correlation analysis of slowly ..."
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Cited by 42 (2 self)
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We used simultaneous electroencephalogram-functional magnetic resonance imaging (EEG-fMRI) and EEG-near infrared spectroscopy (NIRS) to investigate whether changes of the posterior EEG alpha rhythm are correlated with changes in local cerebral blood oxygenation. Cross-correlation analysis of slowly fluctuating, spontaneous rhythms in the EEG and the fMRI signal revealed an inverse relationship between alpha activity and the fMRI-blood oxygen level dependent signal in the occipital cortex. The NIRS-EEG measurements demonstrated a positive cross-correlation in occipital cortex between alpha activity and concentration changes of deoxygenated hemoglobin, which peaked at a relative shift of about 8 s. Our data suggest that alpha activity in the occipital cortex is associated with metabolic deactivation. Mapping of spontaneously synchronizing distributed neuronal networks is thus shown to be feasible. © 2003 Elsevier Inc. All rights reserved.
Interdecadal climate variability and regime-scale shifts in
- Pacific North America, Geophys. Res. Lett
"... Abstract. A transect of climate sensitive tree ring-width chronologies from coastal western North America provides a useful proxy index of North Pacic ocean-atmosphere variability since 1600 AD. Here we use this high-resolution record to identify intervals of an enhanced interdecadal cli-mate signal ..."
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Cited by 40 (1 self)
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Abstract. A transect of climate sensitive tree ring-width chronologies from coastal western North America provides a useful proxy index of North Pacic ocean-atmosphere variability since 1600 AD. Here we use this high-resolution record to identify intervals of an enhanced interdecadal cli-mate signal in the North Pacic, and to assess the timing and magnitude of abrupt shifts in this system. In the con-text of this record, the step-like climate shift that occurred in 1976-1977 is not a unique event, with similar events having occurred frequently during the past 400 years. Furthermore, most of the pre-instrumental portion of this record is char-acterized by pronounced interdecadal variability, while the secular portion is more strongly interannual in nature. If the 1976-1977 event marks a return to this mode of variability there may be signicant consequences for natural resources management in the North Pacic Sector.
Wavelet-generalized least squares: a new BLU estimator of linear regression models with 1/f errors
- NeuroImage
, 2002
"... Long-memory noise is common to many areas of signal processing and can seriously confound estimation of linear regression model parameters and their standard errors. Classical autoregressive moving average (ARMA) methods can adequately address the problem of linear time invariant, short-memory error ..."
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Cited by 40 (0 self)
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Long-memory noise is common to many areas of signal processing and can seriously confound estimation of linear regression model parameters and their standard errors. Classical autoregressive moving average (ARMA) methods can adequately address the problem of linear time invariant, short-memory errors but may be inefficient and/or insufficient to secure type 1 error control in the context of fractal or scale invariant noise with a more slowly decaying autocorrelation function. Here we introduce a novel method, called wavelet-generalized least squares (WLS), which is (to a good approximation) the best linear unbiased (BLU) estimator of regression model parameters in the context of long-memory errors. The method also provides maximum likelihood (ML) estimates of the Hurst exponent
Patterns and sources of multidecadal oscillations in droughtsensitive tree-ring records from the central and southern Rocky Mountains
, 2003
"... [1] Tree-ring records spanning the past seven centuries from the central and southern Rocky Mountains were studied using wavelet analysis to examine multidecadal (>30–70 yr) patterns of drought variation. Fifteen tree-ring series were grouped into five regional composite chronologies based on sha ..."
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Cited by 36 (3 self)
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[1] Tree-ring records spanning the past seven centuries from the central and southern Rocky Mountains were studied using wavelet analysis to examine multidecadal (>30–70 yr) patterns of drought variation. Fifteen tree-ring series were grouped into five regional composite chronologies based on shared low-frequency behavior. Strong multidecadal phasing of moisture variation was present in all five regions during the late 16th century megadrought. Consistent oscillatory modes in the 30–70 yr domain persisted until the mid-19th century in two of the five regions, and wet-dry cycles were apparently synchronous at some sites until the 1950s drought. The 16th/17th century pattern of severe multidecadal drought followed by decades of unusually wet conditions resembles the 1950s drought and post-1976 wet period. The 16th century megadrought, which may have resulted from coupling of a decadal (20–30 yr) Pacific cool phase with a multidecadal warm phase in the subtropical North Atlantic, marked a substantial reorganization of climate variation in the Rocky Mountain region. INDEX TERMS:
