A critical need for the modeling community in the context of glacier-ocean modeling, and particularly for the WAIS, is the availability of an easily accessible, data set with which to drive the models. Prior to forcing with climate-change scenarios, we will establish a climatological, annually-repeating simulation, forced by a ‘common-year’ forcing data set. This data set will consist of appropriate atmospheric, oceanic, glaciological, and bathymetric inputs that will be used as initial and boundary conditions to drive all models. The availability of such standardized, reference forcing data sets, such as the CORE [Large & Yeager, 2009] used to drive global ocean models is common and highly successful in other modeling communities [Griffies et al., 2009].
Our first milestone will be to bring the community together to define and create such a common-year, ice-ocean reference experiment (CIORE) forcing data set. Many of the data sets needed already exist in existing well-known data bases [e.g., NCEP/NCAR, BEDMAP-2, SODA, etc.]. The major gaps are in the oceanography, glaciology, meteorology, and bathymetry along the critical ice-ocean grounding zone of the WAIS.
Past experience with defining ‘common-year’ forcing in other modeling communities has highlighted the issue of dealing with natural, interannual variability. Such communities are often data rich with sufficient observational data to quantify the mean and variance of the initial and boundary conditions of the forcing data set. For the WAIS system, we do not have such data – in fact in the grounding zone there are no observations, with only limited observations further out on the shelf, or inland on the glacier. We plan to work with those who have or will collect relevant observations and to integrate those data sets into our COIRE. Our efforts to define a ‘common-year’ will provide a better baseline than is currently available.
All models will run with COIRE to give us insight into intermodel differences, given identical initial and boundary conditions. This will be instructive, and with dozen or so models in place, we will begin to establish estimates of simulation robustness, and a measure of the variance in our ensemble of models. Later stages of our modeling work will involve the application of IPCC forcing scenarios grafted onto our CIORE forcing data set, so that we can address our key target question.
The first product will be a common-year forcing data set, hosted on an appropriate website. First simulations will focus on steady-state simulations from the various models. Effort will be spent on identifying the commonalities and differences in physics and numerics among all models, as a pathway to understand the similarities and differences in the sea-level change produced by each model under common-year forcing. The next simulations will focus on model runs under climate-change scenarios, and interannual forcing. Recommendations on incorporating best-practices in physics and numerics of ice-sheet – ocean interaction will be shared with global climate modeling centers.