Evaluation of global ocean–sea-ice model simulations based on the experimental protocols of the Ocean Model Intercomparison Project phase 2 (OMIP-2)

Abstract

Abstract. We present a new framework for global ocean–sea-ice model simulations based on phase 2 of the Ocean Model Intercomparison Project (OMIP-2), making use of the surface dataset based on the Japanese 55-year atmospheric reanalysis for driving ocean–sea-ice models (JRA55-do). We motivate the use of OMIP-2 over the framework for the first phase of OMIP (OMIP-1), previously referred to as the Coordinated Ocean–ice Reference Experiments (COREs), via the evaluation of OMIP-1 and OMIP-2 simulations from 11 state-of-the-science global ocean–sea-ice models. In the present evaluation, multi-model ensemble means and spreads are calculated separately for the OMIP-1 and OMIP-2 simulations and overall performance is assessed considering metrics commonly used by ocean modelers. Both OMIP-1 and OMIP-2 multi-model ensemble ranges capture observations in more than 80 % of the time and region for most metrics, with the multi-model ensemble spread greatly exceeding the difference between the means of the two datasets. Many features, including some climatologically relevant ocean circulation indices, are very similar between OMIP-1 and OMIP-2 simulations, and yet we could also identify key qualitative improvements in transitioning from OMIP-1 to OMIP-2. For example, the sea surface temperatures of the OMIP-2 simulations reproduce the observed global warming during the 1980s and 1990s, as well as the warming slowdown in the 2000s and the more recent accelerated warming, which were absent in OMIP-1, noting that the last feature is part of the design of OMIP-2 because OMIP-1 forcing stopped in 2009. A negative bias in the sea-ice concentration in summer of both hemispheres in OMIP-1 is significantly reduced in OMIP-2. The overall reproducibility of both seasonal and interannual variations in sea surface temperature and sea surface height (dynamic sea level) is improved in OMIP-2. These improvements represent a new capability of the OMIP-2 framework for evaluating process-level responses using simulation results. Regarding the sensitivity of individual models to the change in forcing, the models show well-ordered responses for the metrics that are directly forced, while they show less organized responses for those that require complex model adjustments. Many of the remaining common model biases may be attributed either to errors in representing important processes in ocean–sea-ice models, some of which are expected to be reduced by using finer horizontal and/or vertical resolutions, or to shared biases and limitations in the atmospheric forcing. In particular, further efforts are warranted to resolve remaining issues in OMIP-2 such as the warm bias in the upper layer, the mismatch between the observed and simulated variability of heat content and thermosteric sea level before 1990s, and the erroneous representation of deep and bottom water formations and circulations. We suggest that such problems can be resolved through collaboration between those developing models (including parameterizations) and forcing datasets. Overall, the present assessment justifies our recommendation that future model development and analysis studies use the OMIP-2 framework.

Impact of horizontal resolution on global ocean–sea ice model simulations based on the experimental protocols of the Ocean Model Intercomparison Project phase 2 (OMIP-2)

“…The emphasis is on the key metrics used in climate modeling -SST, OHC, sea level, salinity, sea ice extent and volume, and circulations that tend to have global impacts (MOC, ACC, ITF) on the modeled climate. Here these metrics are assessed in a suite of four pairs of low-resolution-high-resolution ocean and sea ice models forced with the latest JRA55-do dataset (Tsujino et al, 2018). These results will provide a useful baseline for future process-focused analyses and ocean model development activities at diverse resolutions.…”

“…The OMIP protocol is an outcome of the Coordinated Ocean-ice Reference Experiments (COREs), which assessed the performance of ocean-sea ice models (Griffies et al, 2009(Griffies et al, , 2014Danabasoglu et al, 2014Danabasoglu et al, , 2016Downes et al, 2015;Farneti et al, 2015;Wang et al, 2016a, b;Ilicak et al, 2016;Tseng et al, 2016;Rahaman et al, 2020) using the atmospheric and river runoff dataset of Large and Yeager (2009). However, this dataset has not been updated since 2009, and a new dataset (JRA55-do; Tsujino et al, 2018) has been developed for the OMIP based on the Japanese Reanalysis (JRA-55) product from Kobayashi et al (2015) to ensure that it is regularly updated. This raw reanalysis product has been substantially adjusted to match reference states based on observations or the ensemble mean of other atmospheric reanalysis products as detailed in Tsujino et al (2018) to create a suitable forcing dataset for ocean and sea ice models, referred to as JRA55do.…”

“…However, this dataset has not been updated since 2009, and a new dataset (JRA55-do; Tsujino et al, 2018) has been developed for the OMIP based on the Japanese Reanalysis (JRA-55) product from Kobayashi et al (2015) to ensure that it is regularly updated. This raw reanalysis product has been substantially adjusted to match reference states based on observations or the ensemble mean of other atmospheric reanalysis products as detailed in Tsujino et al (2018) to create a suitable forcing dataset for ocean and sea ice models, referred to as JRA55do. The continental river discharge is provided by a riverrouting model forced by input runoff from the land surface component of JRA-55 adjusted to ensure similar long-term variabilities as in the CORE dataset (Suzuki et al, 2018).…”

CAS-ESM2.0 Model Datasets for the CMIP6 Ocean Model Intercomparison Project Phase 1 (OMIP1)

“…In the OMIP experiments, the ocean model is coupled with the sea-ice model forced by prescribed atmospheric fields. There are 11 model groups participating in the OMIP experiments according to Tsujino et al (2020). The Co-ordinated Ocean-Ice Reference Experiment II (CORE II) datasets (Large and Yeager, 2009) are applied to force the global ocean/sea-ice models, which is denoted as phase 1 of the physical part of OMIP (OMIP1).…”

A Mechanistic Analysis of Tropical Pacific Dynamic Sea Level in GFDL-OM4 under OMIP-I and OMIP-II Forcings

“…Comparisons to satellite altimeter measurements support an understanding of the processes underlying tropical Pacific sea level variability and trends. Recent studies have shown improved model performance due to updated surface forcing, with particular improvements in the wind field (Taboada et al, 2018), and from refined grid spacing and improved model numerics and physics (Tsujino et al, 2020;Adcroft et al, 2019). Griffies et al (2014) studied model performance and sea level biases for CMIP5-era ocean climate models forced by OMIP-I (CORE).…”