Collaborative Research: Using ocean data assimilation to explore Arctic/subarctic climate variability

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Intellectual merit: Recent decades have seen profound changes in higher latitude climate. This project addresses two goals responding to these changes. The first goal is to develop improved understanding of what past oceanic changes have occurred at high latitude during the past century through application of data assimilation to the sparse historical record of meteorological and oceanic measurements. The first task associated with this goal will be to improve the Simple Ocean Data Assimilation (SODA) data assimilation ocean reanalysis as a tool for high latitude research. This task builds directly on work funded by the predecessor to this grant. This special high latitude effort is required because of the complexities of the region's topography, water masses and currents, the sparse, inhomogeneous oceanic and meteorological observational network, and the important role of sea ice and haline processes. The second task will be to explore the limits the historical data sampling and surface meteorology place on what can be learned about past climate variability through experiments testing the credibility of long ocean reanalyses.The second goal is to examine these results to explore the processes governing interaction between the high latitude ocean, the lower latitude ocean, and the overlying atmosphere, and how these interactions may contribute to climate variability. The remarkable warming the Nordic Seas and Arctic has experienced in the last decade bears similarity to a warm period in the 1920s-1930s. How similar are these two periods, both in magnitude and in impact on the subpolar North Atlantic and on the overlying atmosphere? On shorter decadal timescales the Atlantic Water flowing into the Nordic Seas shows substantial variability partially related to large-scale patterns in meteorology. Related to this are the anomalies of surface salinity such as the Great Salinity Anomaly. What is the origin of this variability, its relationship to the atmosphere, and what is its climate significance? Addressing this second goal will require exploring these mechanisms in coupled atmosphere/ocean/ice models, and in particular the new IPCC-class model runs, using the results of the assimilation studies as guidance. Coupled climate models have complete physics that allow the tracking of the movement of properties such as freshwater and heat through the climate system, while the comparisons to SODA and the historical observations provides information about the realism of the models.Broader impacts: This project will provide the scientific community with an improved analysis of past changes in the upper ocean temperature, salinity, and circulation at high latitude through development and dissemination of an improved SODA ocean reanalysis and improved understanding of its uncertainties. The project?s involvement in the Arctic Ocean Model Intercomparison Project and other venues will help promote the greater knowledge and use of ocean reanalyses generally, and SODA in particular. The second part of this research project, improving understanding of the role of oceanic basin exchanges is a process that needs to be understood in order to develop predictive models. The project will have a substantial educational component by making the data sets, analyses, and computer resources developed as part of this work freely available to the graduate students in the department.