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Dynamically and kinematically consistent global ocean and sea-ice state estimates of the WOCE and satellite era

Monday, May 7, 3:30PM – 4:30PM
ACE 2.302 (AVAYA)

Patrick Heimbach

The advent of satellite altimetry in conjunction with the World Ocean Circulation (WOCE) necessitated a system for observation synthesis into decadal-scale global ocean circulation estimates which are dynamically and kinematically consistent. The emphasis on understanding time-evolving property budgets over climate time scales require closed property budgets and precludes the use of meteorological methods often referred to as "reanalyses." Instead, a state-of-the-art ocean general circulation model is brought to consistency with the diverse types of observations in a least-squares sense using the Lagrange multiplier or adjoint method. The adjoint model is generated through rigorous application of algorithmic differentiation. It can be readily kept up-to-date in a rapidly evolving model development environment and inherits the parallel structure of its parent (nonlinear forward) model. The system accommodates various types of observations, including Argo profiles, satellite SST, altimetry, scatterometry, and gravimetry, as well as hydrography collected from WOCE sections or marine mammals. The state estimates enable inference of climate diagnostics that are not available from individual observations in isolation or from model-only results.

Major current extensions comprise (1) the use of sea ice observations in a joint ocean-sea ice estimation system that covers the polar oceans, and (2) the use of second derivative information to provide formal posterior uncertainty estimates of the estimated state and derived climate indices. Secondary applications of the estimation system include comprehensive sensitivity studies, quantitative observing system design, and investigation of transient non-normal amplification of climate indices with implications for linear predictability.

Short bio:

Patrick Heimbach is a principal research scientist in MIT's department of Earth, Atmospheric and Planetary Sciences (EAPS), and affiliated with, among others, the Center for Computational Engineering, the Center for Global Change Science, the Program in Atmospheres, Oceans and Climate, and the MIT/WHOI Joint Program. Trained as a physicist, he has a wide range of interests, including physical oceanography, glaciology, and climate variability. An overarching theme of his research is the use of quantitative methods for optimal state and parameter estimation from sparse observations and models. Within the "Estimating the Circulation and Climate of the Ocean" (ECCO) consortium he directs the adjoint model development and the production of decadal climate state estimates. Dr. Heimbach is a co-chair of the US CLIVAR working group on Greenland Ice Sheet-Ocean interactions (GRISO), and a member of the US AMOC science team.

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