EASM-3: Collaborative Research: Quantifying Predictability Limits, Uncertainties, Mechanisms, and Regional Impacts of Pacific Decadal Climate Variability

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Climate in the Pacific region varies on decadal timescales, but the mechanisms that control these long-term climate variations are still unclear. If the mechanisms can be better understood, then the uncertainties associated with making climate predictions on these timescales can be assessed more accurately. Decadal variability over the Pacific is of particular interest in the United States due to its downstream influence over the western United States and its direct influence on climate in Alaska. This project addresses the fundamental question of what are the predictability limits, mechanisms, and regional impacts for decadal modes of the Pacific climate system using a hierarchy of climate models and modern statistical tools. The results of this project will be important in assessing how long-term changes in the environment drive changes in economically important variables such as rainfall, soil moisture, snowfall, temperatures, as well as oceanic temperatures, currents and sea levels, which impacts fisheries, agriculture, and coastal infrastructure along the U.S. West Coast and Asian Marginal Seas. The tools developed in this project should be transferable to other global sectors that also exhibit decadal variability. The project team will mentor graduate students and post-docs, whose educational experiences will include cross-disciplinary exposure to ocean science, atmospheric science, and societal impacts that will be unique in this context. Community outreach will include lectures and educational presentations in public forums, mentoring K-12 students, educating grass-roots climate action organizations, informing the media, and posting research results on web pages.There is clearly a large gap in our understanding of what controls Pacific decadal climate variability, what limits the predictability of the flows, and what practical skill might be useful in regional impacts on land and in the ocean. The project team proposes a coordinated research effort to better understand the basic physical dynamics of Pacific decadal variability and assess the skill of Pacific decadal predictability, along with its uncertainties and practical value. The research focuses on Community Earth System Model (CESM), with its vast repository of archived runs supplemented with targeted predictability experiments. The analysis focuses on using sophisticated statistical models (Linear Inverse Models) to identify statistical relations among variables, diagnose physical processes, and isolate potentially predictable components of the flows. It also involves using regional coupled atmosphere-ocean, along with uncoupled ocean and atmosphere models, to enhance the understanding of regional response and its potential for practical use in forecasting. The project brings together scientists skilled with developing decadal climate diagnostics, making both statistical and dynamical predictions, and executing regional coupled climate downscaling and regional high-resolution ocean modeling.