the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
FjordRPM v1.0: a reduced-physics model for efficient simulation of glacial fjords
Abstract. Interactions between ice masses and the ocean are key couplings in the global climate system. In many cases these interactions occur through glacial fjords, which are long, deep, and narrow troughs connecting the open ocean to marine-terminating glaciers. By controlling the fluxes of ocean heat towards the ice sheet and ice sheet freshwater towards the ocean, glacial fjords play an important role in modulating ice sheet mass loss and the impacts of freshwater on ocean circulation. Yet, these dynamics occur at small scales that are challenging to resolve in earth system models and so are they often ignored, represented in an ad-hoc manner, or studied using expensive high-resolution models that are limited in scope. Here, we propose a means of capturing glacial fjord dynamics at negligible computational expense in the form of a "reduced-physics" model (FjordRPM) that resembles a "1.5-dimensional" or box model. We describe the design and physical parameterisations in the model and demonstrate its ability to capture important modes of glacial fjord circulation by comparing it against a general circulation model in idealised and realistic simulations. We suggest that the model is a useful tool for understanding fjord dynamics and a promising approach for representing glacial fjord processes within large-scale models or climate and sea level projection efforts.
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Status: open (until 25 Mar 2025)
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RC1: 'Comment on egusphere-2024-3934', Kenneth Hughes, 30 Jan 2025
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Summary: I'd be perfectly happy as a reviewer to see this paper published as is. In fact, the reason I'm able to get my review in quickly is because the authors made it so easy to read and review.
The paper starts off with a great name for the new model (FjordRPM). Then comes a tidy and concise schematic in Figure 1 that makes clear what the paper is about. Section 2 cleanly layouts the internals of FjordRPM. It pulls together existing model pieces (like the plume model and aspects of iceberg melt), plus a few new things (like the shelf exchange idealization), into a coherent fjord box model. Section 3 gives a high-level overview of how it's implemented as Matlab code. Then Section 4 proves just how good the model is relative to its efficiency: compared to a full 3D MITgcm model, FjordRPM holds it own. (In fact, as someone who uses the MITgcm for fjord simulations, it's almost a bit disappointing that FjordRPM dynamics are captured so well.)
I can see this model (and future iterations alluded to in the paper) being very useful to folks interested in Greenland-wide scales who cannot simulate the fjords themselves, but want to include their effects. Indeed, the clean and clear Github repo with steps to reproduce all the experiments means it'll be easy for someone to pick this up and configure it for their own use.
Excellent work. Ken Hughes, January 2025
Suggestions for improvement
---------------------------As I say, I'm perfectly happy with the paper as is, but you may want to consider the following things
It's good practice to use upright text, not italics, in subscripts and superscripts when they are being used as labels: http://physics.nist.gov/cuu/pdf/typefaces.pdf. This is especially useful for improving the look of longer labels like 'eff', 'above', and 'melt'
Consider removing the Conclusion section. The text in the Discussion in more profound and interesting (and less a repeat of the early sections of the paper). It therefore seems, to me at least, to be a much stronger way to finish the paper. Change the heading 'Discussion' to 'Discussion and Conclusion'
Typo at 590 'that' > 'than'
Citation: https://doi.org/10.5194/egusphere-2024-3934-RC1
Model code and software
FjordRPM v1.0: a reduced-physics model for efficient simulation of glacial fjords Donald Slater, Eleanor Johnstone, Martim Mas e Braga, Neil Fraser, Tom Cowton, and Mark Inall https://doi.org/10.5281/zenodo.14536606
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