Origins of prolonged ocean temperature extremes in the North Pacific

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During the winters of 2013/14 and 2014/15 the Northeast Pacific experienced the warmest ocean temperatures ever recorded in this region. The warm water mass anomaly spread initially throughout the Gulf of Alaska region and later reached the North American coast, covering an area larger than the size of the continental United States. This prolonged multi-year ocean extreme caused dramatic changes in the marine ecosystems including bird and mammal die offs, and harmful algal blooms that contaminated shellfish across Washington, Oregon, and California. The atmospheric changes associated with this extreme event were also implicated in the 2014/2015 strong drought conditions over western North America. The research proposed here is to diagnose the mechanisms underlying the generation and persistence of ocean temperature extremes ('ocean heat waves') in the Northeast Pacific, and to investigate whether these events will become more intense under greenhouse forcing. This proejct will provide a broad range of interdisciplinary scientists with new understandings of the dynamics controlling the 2014/15 North Pacific warming, and of its possible links to climate change. Project investigator Di Lorenzo has acted and will continue to act as interdisciplinary communicator to bridge the climate, physical and biological oceanography communities by making the results of this research available to marine ecosystem scientists through his ties to the California Current Ecosystem LTER (long-Term Ecological Research) and the PICES (North Pacific Marine Science Organization) community. Given the strong interest of resource managers and public in the 2014/15 North Pacific extreme, the principal investigator will compile a set of outreach videos to explain the findings of this research to a broader non-scientific audience. These videos will be posted on the project website and advertised through social media. The model and analyses data will be made available through the Georgia Tech data server and the project website. The project will support the training of female graduate student.By diagnosing the basin- and regional-scale forcing dynamics of multi-year ocean temperature extremes, this project will develop a mechanistic framework to understand the generation, persistence, and evolution of ocean extremes in the Northeast Pacific. This mechanistic framework will not only allow us to interpret the dynamics of recent climate extremes in the Northeast Pacific, but will also provide a physical basis for understanding how such climate extremes will evolve under greenhouse forcing. This proposal aims at (1) diagnosing the basin- and regional-scale mechanisms underlying the generation and persistence of ocean temperature extremes in the Northeast Pacific, including the role of tropical/extratropical climate teleconnections and Pacific decadal variability, and (2) investigating whether there are physical links between these multi-year ocean extremes and greenhouse forcing. The primary tools for this investigation will be observational reanalysis datasets from operational meteorological centers like National Center for Environmental Prediction (NCEP) and the European Centre for Medium-range Weather Forecasts (ECMWF), sensitivity simulations with the NCAR Community Earth System Model (CESM), and the CESM Large Ensemble (LE) data. The CESM ensemble will allow us to clearly separate the internal vs. the anthropogenic-forced changes in North Pacific climate variance, and quantify its significance. Guided by our diagnostic understanding of North Pacific climate in the CESM-LE analyses, we will explore whether our findings are robust across a select set of climate models used for the fifth assessment of the Intergovernmental Panel on Climate Change (IPCC), using both control and carbon-forced simulations available in the Climate Modeling Inter-comparison Project 5 (CMIP5) archive.