Comprehensive evaluation underscores the strengths and areas for improvement in current MITgcm-based Southern Ocean reanalyses.

Reporting by Helen Hill for MITgcm

The Southern Ocean, a critical component of Earth’s climate system, has long posed challenges for scientists aiming to accurately model its complex dynamics. A recent study led by Yoshihiro Nakayama (Dartmouth) set out to evaluate several MITgcm-based ocean reanalyses, among them ECCOv4r5, ECCO LLC270, B-SOSE, and GECCO3. The paper appears in the journal Geoscientific Model Development.

Broadly, the researchers found that the reanalyses under scrutiny generally excel in simulating the time-mean hydrography and ocean circulation of the open Southern Ocean. For instance, the Antarctic Circumpolar Current (ACC) was accurately represented with strengths around 149±11 Sverdrups (Sv), closely matching observational data. Additionally, the positions of the 2°C isotherms and the strengths of the Weddell and Ross Gyres were well-simulated, aligning with observation-based estimates.

However, the study also highlighted some limitations. The reanalyses struggled to accurately capture the temporal evolution of the Southern Ocean, often showing larger trends and excessive warming compared to observational data. Furthermore, all reanalyses failed to reproduce observed hydrographic features on the continental shelf, indicating potential inaccuracies in the simulated physics governing these regions.

Despite these challenges, Nakayama et al found that MITgcm-based ocean reanalyses remain valuable tools for generating ocean lateral boundary conditions for regional high-resolution simulations. The authors recommend that future users of these reanalyses be mindful of their limitations, particularly regarding temporal changes and continental shelf processes.

To find out more about this work​ contact Yoshihiro

Story image: Model-simulated potential temperature, salinity, and stream function for each of the reanalyses models with the World Atlas climatology for comparison – image courtesy the researchers.

About the Researcher

Yoshihiro Nakayama is an Assistant Professor of Engineering at Dartmouth College, specializing in oceanography, polar ocean observations, numerical modeling, and data assimilation. He holds a PhD in Natural Sciences from the University of Bremen, Germany, and has conducted extensive research on the Southern Ocean and Antarctic ice loss. Nakayama’s Lab has been developing ECCO the downscaling simulations for Antarctic continental regions (e.g., Amundsen-Bellingshausen, East Antarctic, etc)

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