An Assessment of Global and Regional Sea Level for Years 1993–2007 in A Suite of Interannual CORE-II Simulations
There are a growing number of observation-based measures of sea level related patterns with the advent of the Argo floats (since the early 2000s) and satellite altimeters (since 1993). These measures provide a valuable means to evaluate aspects of global model simulations, such as the global ocean-sea ice simulations run as part of the interannual Coordinated Ocean-ice Reference Experiments (Griffies et al., 2009, Danabasoglu et al., 2013). In addition, these CORE-II simulations provide a means for evaluating the likely mechanisms causing sea level variations, particularly when models with different skill are compared against each other and observations. We have conducted an assessment of CORE-II simulations from 13 model configurations (Griffies et al., 2013), with a focus on their ability to capture observed trends in ocean heat content as well as the corresponding dynamic sea level over the period 1993-2007.
The CORE-II simulations are designed primarily for studies of interannual variability (Doney et al., 2007, Large and Yeager, 2012). The atmospheric state of Large and Yeager (2009), used as part of the CORE-II air-sea flux calculations, contains interannual satellite-based radiation only after 1983. Over the 15 year period from 1993-2007, observed sea level variations have a large component due to natural variability e.g., Zhang and Church (2012), Meyssignac et al (2012). The CORE-II simulations thus provide a useful means to evaluate interannual variability in ocean-ice models against observations of sea level.
Assessment of the multi-model mean result shares strong similarities with the spatial pattern and the global mean response of dynamic and thermosteric sea level changes respectively. There is a strong similarity between individual model simulations and the multi-model mean, and is suggestive that current generation ocean models are converging on their simulation realism. These results suggest that current ocean-ice only model simulations accurately represent the large-scale ocean circulation and variability that current observing systems are able to measure.
This work provides an important baseline study for which an ocean-centric satellite MIP in CMIP6 may be based.
The utility of ocean sea-ice models to accurately reproduce observed ocean changes over decadal timescales is an open question in climate research. This question has been addressed in the new analysis of Griffies et al. (2014), who have undertaken an assessment of 13 ocean sea-ice models forced using the CORE-II simulation protocol.
Ocean models are very sensitive to the imposed boundary fluxes of heat, water and momentum, which they require in order to replicate observed ocean changes. The study has further extended upon the CORE (Coordinated Ocean-ice Reference Experiments) protocol to allow a direct observation-model Intercomparison, as boundary fluxes from observed and reanalyzed sources are used to replicate observed ocean changes over the 1948-2007 period.
By focusing on the last 15-year period (1993-2007) of the simulations, for which both in-situ and satellite based estimates of ocean state exist, the global mean thermosteric sea level along with the pattern of dynamic sea level changes can be assessed. As models are forced with “observed” boundary fluxes, the modes of atmospherically-forced intrinsic variability are imposed on the models and the observed and modeled fields can be directly compared.
The WCRP/CLIVAR Working Group on Ocean Model Development (WGOMD) is responsible for organizing the Coordinated Ocean-sea ice Reference Experiments. The conceptual and technical details associated with global ocean-sea ice model comparisons have comprised the majority of the group’s deliberations since its inception in 1999. We thank Anna Pirani from the CLIVAR staff for her tireless and gracious support of WGOMD activities.
Much of the analysis in this paper made use of the free software package Ferret, developed at NOAA-PMEL. We thank Frank Bryan, Carolina Dufour, Matthew England, Andy Hogg, Robert Kopp, Angelique Melet, and Ron Stouffer for comments and discussions that have greatly helped this paper. We thank Christophe Cassou for comments on the possible effects from wind errors in their relation to biases in equatorial Pacific sea level patterns. Finally, we thank the critical input from three anonymous reviewers.
NCAR is sponsored by the US National Science Foundation. The ACCESS model is supported by the Australian Government Department of the Environment, the Bureau of Meteorology and CSIRO through the Australian Climate Change Science Programme. E. Fernandez was supported by the BNP-Paribas foundation via the PRECLIDE project under the CNRS research convention agreement 30023488. P.J. Durack was supported by the Regional and Global Climate Modeling Program of the U.S. Department of Energy Office of Science, and his research was performed at LLNL under Contract DE-AC52-07NA27344. A.M. Treguier acknowledges support of the European Commission’s 7th Framework Programme, under Grant Agreement number 282672, EMBRACE project. J. Yin and P. Goddard are supported by NOAA CPO under Grant NA13OAR4310128. D.M. Holland was supported by NYU Abu Dhabi grant G1204.