Tropical Pacific Decadal Variability and Its Impact on the Atmosphere in Climate Models

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Tropical Pacific decadal variability can have large impacts upon the global climate, and it complicates our ability to separate anthropogenically induced trends from natural climate variations. Improved understanding of the mechanisms responsible for such variability is, therefore, fundamental for assessing the predictability of the tropical oceans and their local and remote climate influences. This study will examine tropical Pacific decadal variability in the output of an ensemble of global climate models using runs carried out for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Relevant physical processes will be identified, along with their regions of origin, and these regional forcings will be related to the large-scale atmospheric circulation.The project will also examine the features of decadal variability likely to emerge in future climates, along with the impacts of this future variability on climate variations important to people, such as rainfall over the United States. The work will use a combination of in-depth diagnostics of existing model output and sensitivity experiments using an ocean model. Given the central role of surface wind forcing for decadal variations, these experiments will apply anomalous wind forcing in different areas, in order to identify key forcing regions and key aspects of the anomalous winds at decadal timescales. For climate models with more realistic decadal variations, the associated wind forcing will be related to the large-scale atmospheric circulation to identify precursors of that forcing and large-scale atmospheric anomalies resulting from the tropical sea surface temperature variations. Climate change simulations will be used to examine the characteristics of decadal variability in a warmer climate, along with its global influences.Broader impacts of this work include collaboration with a Ph.D. student at the University of Colorado. Improved understanding of tropical Pacific decadal variability in present and future climates will help in assessing the predictability of persistent droughts over the United States.