Collaborative Research: The Role of Basin Modes in Pacing Pacific Decadal Variability

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project will investigate the hypothesis that Rossby basin modes play a significant role in Pacific Decadal Variability (PDV). Baroclinic Rossby basin modes are natural oscillations of the ocean with very large spatial scales and periods of up to a decade or more, making them of clear interest for understanding climate variability. The proposed work will consist of three main tasks. The first task will be to systematically determine the periods, decay-rates and spatial patterns of basin modes in the presence of the combined effects of (i) basin geometry and bottom topography, (ii) background circulation and stratification, and (iii) Rossby wave instability. As part of this project the Rossby basin modes of a full three-dimensional primitive equation model of the ocean will be computed for the first time. The proposed work will thus push the frontier of how ocean general circulation models are used to understand the climate system. The second task will be to try to detect basin modes in a combination of available data sets including observations, data-constrained model integrations, and unconstrained model integrations. A novel projection technique will be used to detect modal structures in noisy data. The third task will be to test the hypothesis that basin modes play a significant role in PDV by studying the imprint of baroclinic basin modes on the surface heat budget, sea surface temperature and thermocline depth in the tropics , a place of strong coupling between the ocean and the atmosphere, and so determine if the Pacific basin modes modulate the tropical air-sea interaction and ENSO at decadal time scales. Intellectual Merit: The project aims to elevate the concept of basin modes above its roots in Geophysical Fluid Dynamics, and to bring its relevance for decadal climate variability to the test. A novel projection technique will be used (and further developed) to detect dynamically-consistent modal structures in noisy data. In addition, advanced numerical analysis techniques will be applied to the most advanced and realistic ocean models to date, hence pushing the limits of computational analysis.Broader Impacts: The project will enhance the predictability of Pacific Decadal Variability by unequivocally identifying the role of low-frequency Rossby wave basin modes. By improving our understanding of low-frequency variability in the Pacific ocean this project has the potential of greatly enhancing the ability to predict climate and to better manage fisheries. The investigators are committed to integrating their research activities into teaching and educational outreach. Basin-scale waves with oscillation periods of more than a decade are ideally suited to capture the imagination of a public whose acquaintance with ocean waves is likely to be limited to the high-frequency phenomenon of the surf crashing on the beach. At the University of California, Irvine (UCI), Dr. Primeau will continue to contribute to UCI CAMP (promoting minority-student participation in science), and to the NSF-sponsored UCI FOCUS! (Faculty Outreach Collaborations Uniting Scientists, Students, and Schools) program by training elementary-school teachers from minority, high-need school districts. A graduate student at UC Irvine and a post-doc at the New Mexico Consortium will receive training in ocean modeling, advanced numerical analysis, data analysis and statistical methods.