Modeling and Observational Study of Decadal El Nino-Southern Oscillation (ENSO) Modulation and Tropical Pacific Decadal Variability

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The El Nino-Southern Oscillation (ENSO) phenomenon provides an important source of climate predictability on interannual time scales. The research aims for mechanistic understanding of the processes important to the decadal modulation of ENSO and tropical Pacific decadal variability through model experiments and observational analysis. It is hypothesized that the low frequency components of stochastic atmospheric variability in the North and South Pacific, namely, the North Pacific Oscillation (NPO) and Pacific-South American (PSA) variability, independently drive tropical Pacific decadal variability. Furthermore the tropical Pacific decadal variability driven by NPO interacts with ENSO and modulates its amplitude through meridional displacement of the mean intertropical convergence zone (ITCZ). The PSA variability, on the other hand, appears to drive ENSO-like decadal variability associated with the Pacific Decadal Oscillation (PDO), affecting precipitation in the South Pacific convergence zone (SPCZ). These hypotheses will be tested through detailed analysis of climate and atmospheric model experiments. The model results will also be validated with observational analysis of various instrumental data and paleoclimate proxy records for the past 100-200 years. The observational analysis will show if the ITCZ and SPCZ vary independently on decadal-interdecadal time scales and how their decadal variability is associated with the decadal ENSO modulation. The results obtained from the project will not only shed light on the nature of tropical Pacific climate variability but also provide guidance in understanding the uncertainty of future ENSO behavior and in interpreting paleoclimate proxy records of ENSO.