the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Studying multi-scale ocean dynamics and their contribution to water, heat and salt budgets in the South China Sea: evaluation of a high-resolution configuration of an online closed-budget hydrodynamical ocean model (SYMPHONIE version 249)
Ngoc Bich Trinh
Marine Herrmann
Caroline Ulses
Patrick Marsaleix
Thomas Duhaut
Thai To Duy
Claude Estournel
R. Kipp Shearman
Abstract. The South China Sea Throughflow (SCSTF) connects the South China Sea (SCS) with neighboring seas and oceans, transferring surface water of the global thermohaline circulation between the Pacific and Indian oceans. A high resolution (4 km, 50 vertical levels) configuration of the SYMPHONIE ocean model is implemented over this region, and a simulation is performed over a 10 year period (2009–2018). An online computation of each term of the water, heat and salt budgets over the SCS (surface, lateral, and river fluxes and internal variations) is moreover developed. Comparisons with in-situ and satellite data show that the model reproduces correctly the spatial and temporal (from seasonal to interannual) variability of the surface water characteristics and circulation over the SCS, and the vertical distribution of water masses. The added value of an online computation compared to an offline one of water, heat and salt budget is quantitatively demonstrated. Important discards are obtained when computing heat and salt lateral fluxes offline (relative bias of respectively 31 % and 52 % and NRMSE of 32 % and 8 %, for the net heat and salt annual fluxes through the SCS). Considerable differences are also obtained for lateral incoming and outgoing fluxes, with relative biases of 41 %, 38 % and 41 % and NRMSE of 352 %, 226 % and 338 % for annual lateral inflows and outflows of water, heat and salt, respectively.
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Ngoc Bich Trinh et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-547', Anonymous Referee #1, 18 Jun 2023
The authors utilized the SYMPHONIE model's kernel to conduct a simulation of higher resolution (4 km) compared to previous studies. They evaluated the performance of this simulation by comparing it with satellite and field measurements. The errors in online and offline computation of lateral fluxes were estimated. The logical flow of the manuscript is clear. However, based on my evaluation, this simulation did not provide new and insightful information about the dynamics of this large-area marginal sea. Therefore, I cannot support accepting this research in its current stage. I would like to highlight the following major concerns for the authors' consideration:
1) The authors claim that this simulation benefits from higher horizontal resolution, but it is unclear how. Were frequently used models like HYCOM, GLORYS12V1 from CMEMS, and OFES simulation shown to perform poorly compared to the regional simulation presented in the manuscript? It is essential to thoroughly compare this simulation with frequently used models, particularly when the circulations in the study area, such as the South China Sea (SCS), are influenced by complex internal and external forces. If these later simulations performed better than the configurated one, I don’t think a publication of this manuscript will contribute to the community.
2) The circulations in the SCS have not been adequately validated. For instance, the authors mention the significance of the SCS Throughflow, which plays a predominant role in defining the SCS circulation. It is crucial to further validate whether the intensity and structure of this flow are accurately represented in the simulation.
3) The simulation covers the period from 2009 to 2018, and the discussion also focuses on this period. Why was there no mention of the simulation requiring time to spin-up to eliminate distortions caused by abruptly imposed forcings?
4) The computational domain does not include the source region of the Kuroshio current (e.g. the NEC), which extensively intrudes into the SCS through Luzon Strait. Consequently, the dynamics of this important western-boundary current are not adequately addressed. It would be valuable to assess whether the intensity of the Kuroshio intrusion in the Luzon Strait aligns with observations of volume transport.
5) Among the widely used numerical simulation kernels, mass conservation is typically replaced by volume conservation under the incompressible assumption. Therefore, volume should be conserved in the computational domain, while salinity and temperature may not be conserved due to additional sources and sinks. I would appreciate it if the authors could explain why "The variation of heat content HC between times t1 and t2 (ΔHC) is equal to the sum of all heat fluxes exchanged within the SCS domain between t1 and t2" is used for heat balance. Additionally, why are evaporation-precipitation (E-P) and river discharge excluded from the computation of salt flux? Changes in salinity resulting from E-P and river discharge significantly affect the salinity and, consequently, the budget presented in the manuscript.
6) The simulation was forced with Harmonic Constants from FES2014b, and then the simulated heat content (HC) was compared to FES2014b itself. I may suggest the authors collect record of tidal elevation from tidal gauges and conduct validation.
Citation: https://doi.org/10.5194/egusphere-2023-547-RC1 -
RC2: 'Comment on egusphere-2023-547', Anonymous Referee #2, 18 Jul 2023
This manuscript presents a study on the implementation and evaluation of a high-resolution hydrodynamic model (SYMPHONIE) over the South China Sea (SCS). The authors simulate a 10-year period and successfully replicate observed circulation patterns and water masses in the SCS. The introduction of an online computation method to assess water volume, heat, and salt budgets adds strength to the manuscript. However, there are some areas that require improvement. First, the manuscript should clearly highlight the role and advantages of the 4 km configuration, enhancing the scientific significance of the study. Second, Section 3 needs restructuring to ensure logical flow and provide a more detailed evaluation of the South China Sea Throughflow (SCSTF). Lastly, reconsidering the title to clarify the "scale" aspect would be beneficial. By addressing these issues, the manuscript has the potential to make a valuable contribution to the scientific literature on South China Sea dynamics and ocean modeling community.
Major Comments:
- The title of this manuscript is confusing and could be misunderstood as referring to different spatial scales of ocean dynamics rather than temporal scales. It is recommended to clarify this in the title to avoid confusion.
- The manuscript mentions the use of a 4 km resolution, which is an outstanding feature of the configuration. It would be more meaningful to explicitly highlight the role and advantages of this high-resolution approach in the manuscript. This will enhance the significance of the "multi-scale ocean dynamics" concept, incorporating both temporal and spatial scales.
- The authors claim that the 4 km configuration in the South China Sea (SCS) is developed, but it is important to explain the advantages of this resolution compared to coarser resolution models. Describing these advantages will enhance the scientific significance of the manuscript.
- The structure of Section 3 is unclear. The title of Section 3.2 ("surface characteristics") overlaps with the title of Section 3.1 ("tide"), and the title of Section 3.2.3 is inconsistent with other subsection titles. It is recommended to restructure Section 3 to make it more coherent and clear.
- The analysis of Mixed Layer Depth (MLD) in Section 3.4 is interesting, revealing a robust shallower bias due to wind speed. However, considering the higher resolution, a deeper MLD might be expected, particularly in winter. It would be valuable to compare the results of the 4 km configuration with a coarser-resolution configuration.
- Since the South China Sea Throughflow (SCSTF) is mentioned as a major topic at the beginning of the manuscript, a detailed evaluation of all inflows and outflows through different straits would be expected. However, Section 3 (model evaluation) does not address these throughflows. It is recommended to include an evaluation of the SCSTF in Section 3.
Minor Comments:
- Maintain consistency in the expression of water volume, using consistent terminology throughout the manuscript (e.g., water, volume, or water volume).
- In Line 218, consider including river fluxes in Section 2.2.2 (lateral fluxes) for better organization.
- In Figure 2, it is difficult to discern the difference between the simulation and tidal product. Including a column for bias would enhance clarity.
- Figure 4 should include the bias information. Adding the bias to the figure will improve interpretation.
- In Lines 312, 314, 361, 408, 479, etc., add units for the variables.
- In Line 396, consider revising to "Therefore, our simulation accurately represents..."
- The numbering in the caption of Figure 7 is incorrect, as "(c)" is used twice. Adjust the numbering accordingly.
- Maintain consistency in formatting, ensuring that there is either a space or no space between paragraphs throughout the manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-547-RC2
Ngoc Bich Trinh et al.
Ngoc Bich Trinh et al.
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