14 Jul 2023
 | 14 Jul 2023

Resolving the mesoscale at reduced computational cost with FESOM 2.5: efficient modeling approaches applied to the Southern Ocean

Nathan Beech, Thomas Rackow, Tido Semmler, and Thomas Jung

Abstract. Several cost-efficient, high-resolution modeling approaches are applied to simulations of the Southern Ocean in past, present, and future climates. The results are compared with an ensemble of medium-resolution, eddy-present simulations and evaluated based on their ability to reproduce observed mesoscale activity and to reveal a response to climate change distinct from natural variability. The high-resolution simulations reproduce the observed magnitude of Southern Ocean eddy kinetic energy (EKE) well, but differences remain in local magnitudes and the spatial distribution of EKE. The coarser, eddy-present ensemble simulates a similar pattern of EKE but underrepresents observed levels by 50 %. Five years of simulated data in each time period is found to produce consistent results when evaluating mean conditions and assessing change in the region as a whole. At 1 °C of warming, the high-resolution simulations produce no change in overall EKE, in contrast to the increase projected by the eddy-permitting ensemble and despite full ensemble agreement. At 4 °C of warming, both datasets produce consistent levels of EKE rise in relative terms, although not absolute magnitudes, as well as an increase in EKE variability. Simulated EKE rise is concentrated where flow interacts with topographic features in regions already known to be eddy-rich. Regional EKE change in the high-resolution simulations is consistent with changes seen in at least four of five eddy-permitting ensemble members at 1 °C of warming, and all ensemble members at 4 °C. However, substantial noise would make these changes difficult to distinguish from natural variability without an ensemble.

Nathan Beech et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1496', Mark R. Petersen, 27 Aug 2023
    • RC2: 'Reply on RC1', Mark R. Petersen, 27 Aug 2023
  • CEC1: 'Comment on egusphere-2023-1496', Juan Antonio Añel, 05 Sep 2023
    • CC1: 'Reply on CEC1', Thomas Rackow, 06 Sep 2023
      • CEC2: 'Reply on CC1', Juan Antonio Añel, 06 Sep 2023
  • RC3: 'Comment on egusphere-2023-1496', Anonymous Referee #2, 11 Sep 2023

Nathan Beech et al.

Data sets

Eddy kinetic energy from FESOM SO3 simulations Nathan Beech

Code used for data analysis and visualization Nathan Beech

Nathan Beech et al.


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Short summary
Ocean models struggle to simulate small-scale ocean flows due to the computational cost of high-resolution simulations. Several cost-reducing strategies are applied to simulations of the Southern Ocean and evaluated with respect to observations and traditional, lower-resolution modelling methods. The high-resolution simulations effectively reproduce small-scale flows seen in satellite data and are largely consistent with traditional model simulations regarding their response to climate change.