| 18 May 2026
A high-resolution, submesoscale-resolving ocean model of South East Queensland (ROMS v4.2)
Abstract. The ocean exhibits a continuum of motions spanning basin-scale circulation to micro-scale turbulence where between mesoscale eddies and small-scale turbulence lies the submesoscale (∼0.1–10 km, hours-days). The submesoscale is characterised by fronts, filaments and small coherent vortices that arise from instabilities of mesoscale currents, interactions with topography, and buoyancy forcing. These processes restratify the upper ocean while simultaneously enhancing vertical tracer exchange through intense vertical velocities concentrated at density gradients. In the East Australian Current, the western boundary current of the South Pacific Gyre, the jet accelerates and interacts with the continental shelf off South East Queensland, creating conditions favourable for submesoscale activity. Yet these processes remain unresolved and unexplored in existing regional simulations: mesoscale regional models do not resolve energetic frontal processes, high-resolution coastal models lack realistic offshore forcing, and observations alone are insufficient to constrain the three-dimensional subsurface circulation. Here, we present a submesoscale-permitting implementation of the Regional Ocean Modelling System (ROMS v4.2) for the EAC jet intensification region offshore of South East Queensland and northern New South Wales, Australia. We demonstrate that our model generates energetic fronts and filaments along the continental shelf edge, while maintaining surface and subsurface mesoscale hydrographic structure consistent with observations. Relative to mesoscale-resolving simulations, the configuration exhibits substantially increased hotspots of divergence, vorticity and vertical velocity variance, together with a flatter kinetic energy spectrum indicative of resolved submesoscale dynamics. A demonstration of the continental shelf break in the vicinity of K'gari shows the accelerating jet interacting with coastal promontories and the shelf break, producing localised and persistent submesoscale activity. This configuration enables investigation of submesoscale emergence and interaction with the mesoscale circulation, including jet-shelf modification, cross-shelf exchange and energy transfer across scales. This approach provides a pathway to quantify energy pathways and ocean dynamics, with applications extending beyond the East Australian Current to other western boundary current systems.
General comments
The manuscript, "A high-resolution, submesoscale-resolving ocean model of South East Queensland (ROMS v4.2)," presents a new high-resolution ocean model covering southeast Queensland and northern New South Wales, developed to realistically represent submesoscale processes in a region where the East Australian Current interacts with the continental shelf. The authors provide a comprehensive model evaluation using a wide range of both surface and subsurface observations. They also demonstrate that the high-resolution SEQld ROMS simulation captures substantially more kinetic energy within the mesoscale and submesoscale bands than coarser-resolution model and observation.
Although the evaluation identifies some model deficiencies, including a cold bias over the shelf and discrepancies in volume transport magnitude and phase relative to observations, these limitations are expected. As the model does not employ data assimilation, it is not intended to reproduce ocean features at their exact time and location. Rather, its purpose is to provide a dynamically consistent and realistic representation of the regional circulation and associated submesoscale processes.
Overall, this is a well-written and easy to follow manuscript describing a valuable modelling framework that will benefit future studies in the region. I recommend publication after the authors address the comments and suggestions provided below.
Specific comments
Introduction
L66 and L73: Regarding "intensification region" and "intensification zone", I find this terminology confusing. First, because your model domain covers much more than just the so-called intensification zone. The intensification zone is a specific area in the northern part of your domain. Second, it has been shown that the EAC jet intensifies poleward from 27.5°S to 32°S, reaching its maximum at 32°S (Kerry, 2020). Since your simulation only covers the year 2012, you do not have sufficient seasonal, interannual, and decadal variability to conclude that this is consistently the region where the jet intensifies. I recommend specifying the latitude where the intensification occurs, e.g. "jet intensification at 25°S" or "northern jet intensification", and using this terminology consistently throughout the manuscript.
L73: "... numerical ocean model of the EAC jet intensification zone." Again, your model covers almost the entire EAC jet, not only the region where it intensifies around 25°S. Please revise this throughout the manuscript wherever it appears.
Model description
L88: For a more logical structure, begin with the model simulation period (move the first sentence of the paragraph starting at L124, leaving the "Model spin-up..." sentence to be included with the forcing description). Then describe the model domain (L95–97: "The model domain..."). Move the descriptive paragraph beginning at L105 (key model features) to before the description of the vertical stretching. Then present the horizontal resolution, vertical stretching, lateral and surface forcing, initial conditions, and finally the model spin-up.
Model evaluation and results
L147, L153 and L180: In all three cases, the manuscript overlooks the fact that the model exhibits considerably cooler temperatures on the shelf between 27°S and 31°S, while attributing significant errors mainly to the coarse-resolution products. Although you used RAMSSA SST, OSTIA would likely be a better observational product for this region. Since you state in L159 that the model "may in fact be closer to reality than implied by the calculated RMSE...", I suggest repeating the SST comparison using OSTIA to determine whether the observed shelf cooling is also present in that product.
Submesoscale dynamics
Technical comments
Abstract
L1–5: This section is rather long for an abstract. It could be shortened by providing a more concise explanation of what submesoscale processes are and why they are important. Some of this material could instead be moved to the Introduction.
L6: "... the jet accelerates and interacts with the ..." Please provide more context. Where does it accelerate? Does it only interact with the shelf when it accelerates?
L8: "...in existing regional simulations" — do you mean simulations for southeast Queensland specifically, or for the broader region?
L11: "...for the EAC jet intensification region" Again, the model is not limited to the jet intensification region; it covers the entire jet extension. Consider rephrasing to something like "for the EAC jet-dominated region (latitude range)."
L14: "... increased hotspots of divergence ..." Divergence of what? Please clarify.
L15: "... flatter kinetic energy spectrum" Flatter where? Please provide more context.
L16: "... vicinity of K'gari" Please include the latitude.
L17: "This configuration" Which configuration? Please be specific.
L18: "...jet-shelf modification..." This expression is unclear. Please clarify what is meant.
L19: "This approach" Which approach? Please state it explicitly.
L19: "pathway" is repeated twice in close succession.
Introduction
L25: "... sustained observations of submesoscale processes remain challenging." Please briefly explain why they remain challenging.
L32: "... horizontal strain and extension" Please clarify what is meant by "extension".
L42–43: "... strongly influences ocean conditions ..." Please provide more context on how the EAC influences ocean conditions.
L44–50: Consider adding the circulation schematic to Figure 1 and referring to it here.
L54: The citation displayed as Sloyan et al. (2024) should be Chapman et al. (2024).
L65: "Yet" is repeated. Please reword.
Model description
L125: The hyperlink for Sloyan et al. (2024) points to Chapman et al. (2024). Please check this throughout the manuscript.
Model evaluation and results
Figure 2
L128: Since there is only one subsection, I recommend removing subsection 3.1.
L129: Remove "this" from "We evaluate the ability of this SEQld ROMS..."
L150: Include the region definitions in the text rather than only in the Figure 3 caption, and briefly justify the chosen boundaries.
L160: Add (Figure 1) at the end of the sentence.
Figure 3 caption
Figure 4
L179: Replace the parentheses around "The biases..." with commas, as this is relevant information and does not require parentheses.
Submesoscale dynamics
Figure 5
Caption
Paragraph beginning at L202
Figure 6
L208: Replace our model with SEQld ROMS.
L211: Delete "the" from "to expect time slices from the SEQld ROMS".
L212: End the sentence after metrics. Begin the following sentence with "We compare annual-mean fields..."
Move the magnitude strain equation from L218 to its first mention in L213.
L213: Explain why the analysis is averaged over the upper 100 m.
L215: Add respectively in (Figure 6a,d, respectively).
L262: Add respectively to (Figure 8a,b, respectively).
Discussion and conclusions