Submitted as: model experiment description paper
25 Apr 2022
Submitted as: model experiment description paper | 25 Apr 2022
Status: this preprint is currently under review for the journal GMD.

Observing system simulation experiments reveal that subsurface temperature observations improve estimates of circulation and heat content in a dynamic western boundary current

David E. Gwyther1, Colette Kerry1, Moninya Roughan1, and Shane R. Keating2 David E. Gwyther et al.
  • 1Coastal and Regional Oceanography Lab, School of Biological, Earth and Environmental Sciences, UNSW Sydney, Sydney, NSW, Australia
  • 2School of Mathematics and Statistics, UNSW Sydney, Sydney, NSW, Australia

Abstract. Western boundary currents (WBCs), form the narrow, fast-flowing poleward return flows of the great subtropical ocean gyres and are sources of rapidly varying mesoscale eddies. Accurate simulation of the vertical structure, separation latitude, and ocean heat content of WBCs is important for understanding the poleward transport of heat in the global ocean. However, state estimation and forecasting in WBC regions, such as the East Australian Current (EAC), the WBC of the South Pacific subtropical gyre, is challenging due to their dynamic nature and lack of observations at depth. Here we use Observing System Simulation Experiments to show that subsurface temperature observations in a high eddy kinetic energy region yield large improvement in representation of key EAC circulation features, both downstream and 600 km upstream of the observing location. These subsurface temperature observations (in concert with sea surface temperature and height measurements) are also critical for correctly representing ocean heat content along the length of the EAC. Furthermore, we find that a more poleward separation latitude leads to an EAC and eddy field that is represented with far reduced error, compared to when the EAC separates closer to the equator. Our results demonstrate the importance of subsurface observations for accurate state estimation of the EAC and ocean heat content that can lead to marine heatwaves. These results provide useful suggestions for observing system design under different oceanographic regimes, for example, adaptive sampling to target high energy states with more observations and low energy states with fewer observations.

David E. Gwyther et al.

Status: open (until 22 Jun 2022)

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David E. Gwyther et al.

David E. Gwyther et al.


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Short summary
The ocean flows southward along the south-eastern coast of Australia in a narrow, rapid current called the East Australian Current (EAC) before meandering and forming rotating bodies of water called eddies. Using computer simulations we tested how different kinds of ocean measurements and locations might improve models of the EAC. We suggest future observing strategies and highlight the importance of subsurface observations for understanding western boundary currents.