This project extends an on-going effort (SODA: Simple Ocean Data Assimilation) to explore the potential as well as the limitations of modeling and data assimilation directed toward reconstruction of a centennial analysis of ocean circulation using the Parallel Ocean program (POP). The domain is the global ocean, with an emphasis on the upper ocean where the observational record is more substantial. The main time period is the second half of the last century (1950-2007) with an eye to expand it to the last century if it can established that there are enough observations in the first half of the century to provide reliable estimate of the state of the ocean.. The first effort is to assemble the observations and surface forcing data sets needed for this reanalysis. Indeed, the project is motivated by a corresponding effort by meteorologists to produce a centennial atmospheric reanalysis. A thorough investigation of the error statistics of information that goes into the assimilation will be conducted. The second effort is to explore a change to a more sophisticated assimilation scheme based on the Local Ensemble Transform Kalman Filter. This change would allow properties of the data assimilation such as temperature-salinity error covariances to evolve throughout the reanalysis period, rather than being fixed a priori. Attention will also be focused on improving representation of the structure of the mixed layer. The results of the reanalysis experiments will then be used to explore the structure and evolution of a variety of ocean climate signals such as the El Nino?Southern Oscillation (ENSO) in the Pacific Ocean and decadal variability in the global oceans. The overall goal is to explore the extent to which ocean data assimilation may be used to produce a reference climate for the oceans that in turn can serve as the basis for examining other physical, chemical, and biological analysis products, for providing the large-scale context for observation sets, as well as for studies of the ocean?s contribution to climate variability.
Intellectual merit: This research will result in understanding of the potential of a centennial reanalysis of the physical state of the ocean with emphasis on the upper 1000m. Centennial reanalyses will be produced and made available to the community, along with the forcing and ocean data sets. The intellectual merit lies in the potential of this kind of reanalysis to open up new questions regarding the ocean?s role in climate variability. The results will be used to carry out diagnostic examination of variability on seasonal, interannual, and decadal timescales including examination of covariations of atmospheric climate variability. Finally, the ocean reanalysis product will be compared to independent observation sets in order to learn about the uncertainties in the reanalysis.
Broader impacts: SODA reanalyses are currently being used by researchers from around the world and there should be considerable interest in these new reanalyses, both because of the longer period of coverage and because of the new assimilation scheme. The set of reanalysis experiments resulting from this work will be made available to the community and will offer many opportunities for students and researchers to explore ocean climate variability. In addition to training graduate students at the University of Maryland and at Texas A&M University in ocean data assimilation, the reanalysis can be used as the foundation for graduate students at other institutions and as a resource for classroom teaching.
