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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 37 (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 socalled 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
LongLead Prediction of Pacific SSTs via Bayesian Dynamic Modeling
, 2000
"... Tropical Pacific sea surface temperatures (SST) and the accompanying El Niño Southern Oscillation (ENSO) phenomenon are recognized as significant components of climate behavior. The atmospheric and oceanic processes involved display highly complicated variability over both space and time. Researcher ..."
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Cited by 19 (6 self)
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Tropical Pacific sea surface temperatures (SST) and the accompanying El Niño Southern Oscillation (ENSO) phenomenon are recognized as significant components of climate behavior. The atmospheric and oceanic processes involved display highly complicated variability over both space and time. Researchers have applied both physically derived modeling and statistical approaches to develop longlead predictions of tropical Pacific SSTs. The comparative successes of these two approaches are a subject of substantial inquiry and some controversy. In this article, we present a new procedure for longlead forecasting tropical Pacific SST fields that expresses qualitative aspects of scientific paradigms for SST dynamics in a statistical manner. Through this combining of substantial physical understanding and statistical modeling and learning, our procedure acquires considerable predictive skill. Specifically, a Markov model, applied to a loworder (EOFbased) dynamical system of tropical Paci...
Quantifying Persistence in ENSO
 J. Atmos. Sci
, 1999
"... The seasonal dependence of predictability in ENSO manifests itself in the socalled spring barrier found in the cyclostationary lag autocorrelations, or persistence. This work examines the statistics of persistence, with particular focus on the phaseofyeardependent pattern found in ENSO data, t ..."
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The seasonal dependence of predictability in ENSO manifests itself in the socalled spring barrier found in the cyclostationary lag autocorrelations, or persistence. This work examines the statistics of persistence, with particular focus on the phaseofyeardependent pattern found in ENSO data, the barrier. Simple time series of one sine wave produce a barrier if the frequency is a biennial cycle or one of its harmonics. Time series of two sine waves produce a barrier if one frequency is a biennial cycle or a harmonic thereof. They additionally produce a barrier if their frequencies sum to unity. Time series with continuous but narrow spectral peaks at barrierproducing frequencies produce barriers only if the phase angles vary slowly or coherently across the peaks. The shape of the barrier seen in these simple time series is used to construct a model persistence map, which is a combination of an idealized barrier and the persistence of a rednoise process. A nonlinear least ...
PARTICLE FILTERS FOR SYSTEM IDENTIFICATION WITH APPLICATION TO CHAOS PREDICTION
"... Abstract: The theory of the particle filter, or sequential Monte Carlo methods, has made substantial progress the last decade. The number of applications has increased substantially the last three years, in particular in navigation and telecommunication areas. In this contribution, we will first poi ..."
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Abstract: The theory of the particle filter, or sequential Monte Carlo methods, has made substantial progress the last decade. The number of applications has increased substantially the last three years, in particular in navigation and telecommunication areas. In this contribution, we will first point out how the particle filter can be used for system identification, using a quite general problem formulation, and it is pointed out in which kind of application the particle filter can be an attractive alternative to classical system identification methods. This is then demonstrated on prediction of time series arising from chaotic dynamical systems. The specific dynamical system considered is the so called logistical map with an unknown parameter, which belongs to the chaotic regime.
Locking of El Niño’s Peak Time to the End of the Calendar Year in the Delayed Oscillator Picture of ENSO
, 1996
"... El Niño events owe their name to their tendency to be locked to the seasonal cycle. A simple explanation is proposed here for the locking of the peak of ENSO’s basinscale warming to the end of the calendar year. The explanation is based on incorporating a seasonally varying coupled ocean–atmosphere ..."
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El Niño events owe their name to their tendency to be locked to the seasonal cycle. A simple explanation is proposed here for the locking of the peak of ENSO’s basinscale warming to the end of the calendar year. The explanation is based on incorporating a seasonally varying coupled ocean–atmosphere instability strength into the delayed oscillator mechanism for the ENSO cycle. It is shown that the seasonally varying amplification of the Rossby and Kelvin ocean waves by the coupled instability forces the events to peak when this amplification is at its minimum strength, at the end of the calendar year. The mechanism is demonstrated using a simple delayed oscillator model and is further analyzed using the Cane–Zebiak model. Being based on the oversimplified delayed oscillator paradigm of ENSO, the proposed mechanism cannot be expected to fully explain the locking of observed events to the end of the year. However, the wave dynamics perspective it offers to approaching the ENSO phaselocking problem may serve as a first step toward a fuller explanation based on more realistic models and additional data analysis. 1.
ON THE ROLE OF INTERNAL ATMOSPHERIC VARIABILITY IN ENSO DYNAMICS
, 2005
"... ... develop a quantitative test to validate the null hypothesis that lowfrequency variation of ENSO predictability may be caused by stochastic processes. Three “perfect model scenario ” prediction experiments are carried out, where the model is forced either solely by stochastic forcing or additi ..."
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... develop a quantitative test to validate the null hypothesis that lowfrequency variation of ENSO predictability may be caused by stochastic processes. Three “perfect model scenario ” prediction experiments are carried out, where the model is forced either solely by stochastic forcing or additionally by decadalvarying backgrounds with different amplitudes. These experiments indicate that one can not simply reject the null hypothesis unless the decadalvarying backgrounds are unrealistically strong. The second part of this dissertation investigates the extent to which internal atmospheric variability (IAV) can influence ENSO variation, and examines the underlying physical mechanisms linking IAV to ENSO variability with the aid of a newly developed coupled model consisting of an atmospheric general circulation model and a ZebiakCane type of reduced gravity ocean model. A novel noise filter algorithm is developed to suppress IAV in the coupled model. A long control coupled simulation, where the filter is not employed, demonstrates that the coupled model captures many statistical properties of the observed ENSO behavior. It further shows that the development of El Niño is linked to a boreal spring