The development and validation of a global 1/32&deg; surface wave-tide-circulation coupled ocean model: FIO-COM32

Xiao, Bin; Qiao, Fangli; Shu, Qi; Yin, Xunqiang; Wang, Guansuo; Wang, Shihong

doi:https://doi.org/10.5194/gmd-2022-52

Preprints

https://doi.org/10.5194/gmd-2022-52

Preprints

Submitted as: model evaluation paper

15 Mar 2022

Submitted as: model evaluation paper | 15 Mar 2022

Status: this preprint was under review for the journal GMD but the revision was not accepted.

The development and validation of a global 1/32° surface wave-tide-circulation coupled ocean model: FIO-COM32

Bin Xiao^1,2,3, Fangli Qiao^1,2,3, Qi Shu^1,2,3, Xunqiang Yin^1,2,3, Guansuo Wang^1,2,3, and Shihong Wang^1,2,3 Bin Xiao et al.

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¹First Institute of Oceanography, and Key Laboratory of Marine Science and Numerical Modeling, Ministry of Natural Resources, Qingdao 266061, China
²Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology, Qingdao 266237, China
³Shandong Key Laboratory of Marine Science and Numerical Modeling, Qingdao 266061, China

Received: 24 Feb 2022 – Discussion started: 15 Mar 2022

Abstract. Model resolution and the included physical processes are two of the most important factors that determine the realism of the ocean model simulations. In this study, a new global surface wave-tide-circulation coupled ocean model FIO- COM32 with resolution of 1/32° × 1/32° is developed and validated. Promotion of the horizontal resolution from 1/10° to 1/32° leads to significant improvements of the simulations of surface eddy kinetic energy (EKE), fine structures of sub- mesoscale to mesoscale movements and the accuracy of simulated global tide. The non-breaking surface wave-induced mixing (Bv) is proved to be an important contributor that improves the agreement of the simulated summer mixed layer depth (MLD) of the model and the Argo observations even with high horizontal resolution of 1/32°, the mean error of the simulated mid-latitude summer MLD is reduced from -4.8 m in numerical experiment without Bv to -0.6 m in experiment with Bv. With the global tide is included, the global distributions of internal tide can be explicitly simulated in this new model and is comparable to the satellite observations. Comparisons using Jason3 along-track sea surface height (SSH) wave-number spectral slopes of mesoscale ranges show that internal tide induced SSH undulations is a key factor contributing to the substantially improved agreement of model and satellite observations in the low latitude and low EKE regions. For ocean model community, surface wave, tidal current and ocean circulation have been separating into different streams for more than half century. It should be the time to merge these streams for new generation ocean model development.

Bin Xiao et al.

Status: closed

RC1: 'Comment on gmd-2022-52', Baylor Fox-Kemper, 07 Apr 2022

The paper "The development and validation of a global 1/32° surface wave-tide-circulation coupled ocean model: FIO-COM32" by Bin Xiao et al. describes the initial stages of developing a 1/32 degree version of the FIO model. Based on past successes of the FIO models, the Bv scheme is prominently discussed, as is the incorporation of tides. The paper focusses on the last year of two 2-3-year simulations EXP1, not including tides or Bv waves, and EXP2 including both. Two other important simulations are noted for future work.

In general, the paper describes a milestone of expensive work in progress, and for this reason many aspects of incomplete experimental design may be overlooked. However, some important theoretical aspects of the work are not mentioned (although they are relevant) and some additional analysis would be informative. Here is my short list of these issues:

1) In the mesoscale 1/10 degree model, wave effects on currents (WEC) and current effects on waves (CEW) are not expected to be very strong. However, as shown in McWilliams & Fox-Kemper (2013: http://dx.doi.org/10.1017/jfm.2013.348) and Suzuki et al. (2016: http://dx.doi.org/10.1002/2015JC011566) the expected magnitude of the WEC effects can be estimated using the epsilon parameter. Given the interest of FIO modeling to include wave impacts in their modeling family, it would be very interesting to see the epsilon parameter estimated in the MASNUM-1/10 and MASNUM-1/32 models.

2) It is not mentioned whether the EXP1 or EXP2 currents refract/diffract/affect the waves in the 1/32 models. It is well known from operational wave modeling that these effects become important roughly in the 1/10 resolution range. They are very important at 1/32 degree resolution. Some estimate of these effects would strengthen this work and provide impetus for a coupled wave-ocean simulation at this resolution to come.

3) Given the offline MASNUM calculation, rather than the directly coupled MASNUM-1/32, it is probably impossible to include both the WEC and CEW effects in the model. However, points 1&2 would show the need for such improvements. This is more interesting than the Bv parameterization result, which shows that small-scale turbulence parameterizations still affect simulations at this resolution. That is not surprising, given that those small-scale turbulence remain far below the resolution at 1/10, 1/32, and even 1/300 degree resolutions. What is more interesting as wave effects over the range of scales from 1/10 to 1/32 is the wave-current coupling.

A) Aside from waves, the new information here primarily results from inclusion of tides. It is an interesting result that tides are significantly improved in the 1/32 degree over 1/10 degree model. However, most of the key metrics discuss only the coherent tides (e.g., Fig 5). As 1/32 degree current calculations could interact much more strongly with tides than the 1/10 degree model, some mention of enhanced incoherent tides would be interesting (and found from a straightforward comparison between EXP1 and EXP2).

B) There is no discussion of the subgrid damping used and how it scales with resolution. Furthermore, a power spectrum showing the rotational and divergent power spectra contributions would be extremely valuable in understanding how the 1/10 and 1/32 models differ at small scales. This information together with more information about the damping would be valuable in understanding the choices made and their consquences, as well as the effective resolution of the vortical and wave/tide modes. This could supplement Fig 9 in a meaningful way, revealing more of the dynamics underpinning the better match of EXP2 to Jason than EXP1.

i) For a submesoscale-permitting model, it would be nice to see what submesoscales are expected to be permitted at 1/32 resolution. The stronger submesoscales in wintertime are now customary, but the weaker submesoscales in summer may be illustrating the limits of 1/32 resolution. It would be nice to include a discussion of Dong et al. (2020: http://dx.doi.org/10.1175/JPO-D-20-0043.1), along with some estimation from the MLD analysis as to the scale of submesoscale baroclinic instabilities. It would be particularly interesting to know if the Bv scheme deepens the MLD or mixes the stratification of the ML enough to have a detectable effect on MLI scale and whether it is more resolvable using Bv. Dong et al. has a similar analysis comparing MLI scales under different boundary layer schemes.

Citation: https://doi.org/10.5194/gmd-2022-52-RC1
RC2:
'Comment on gmd-2022-52', Anonymous Referee #2, 19 Apr 2022
This paper summarizes two high-resolution experiments at 1/32 degree with and without tides. The simulations are spun up for 3 years and diagnostics are performed over the last two years.

This is a major computational exercise and the results are worth documenting. However, as presented, most of the results are expected and in agreement with previous studies. Perhaps the most novel result is the outcome of adding tides which leads to a better agreement between satellite-measured and modeled power spectra. It is indeed nice to see that an increase in resolution leads to a better distribution and a higher magnitude of EKE, but for this paper to be publishable, it needs to go beyond a simple show and tell and provide new insights by performing more in depth analysis of the results and differences.

Specifically,

What does 1/32 gives you in terms of which physical processes are better resolved? It is probably marginal in terms of the submesoscale, so do you see a difference in mixed layer instabilities between 1/10 and 1/32? Is the increase of EKE because of a stronger mesoscale field (lower viscosity) or the addition of submesoscale features?

You allow for only one year spin up from the data assimilative 1/10 run. Is the KE in steady state? Is it sufficient for a mechanical adjustment?

What is the T and S bias after 3 years? You do not use any relaxation to surface salinity which is known to lead to a significant drift in salinity. Can this be quantified? This may not be the main focus of the paper, but it is of importance as it impacts the 3D T and S distribution and strength of the western boundary currents.

This is more of a comment. You use relative wind which is known to have an eddy killing effect (Renault et al., 2019). This is reflected in a modeled EKE is lower than the smooth satellite observed geostrophic EKE.

Line 62: What do you mean by “it is necessary to validate the effect of Bv”? What is the exact question being answered here? Is Bv still effective at 1/32? Do you have any reason what it should not? Is the impact of adding of Bv at 1/10 similar to that of 1/32? Is the mixed layer physic responding differently at 1/10 versus 1/32 (in other word, what is the impact on the MLD of resolving smaller oceanic features?)?

Snapshots are not representative of a solution. Improvements in western boundary current separation, extent and EKE need to be quantified by comparison to observations, not just stating that they qualitatively look better. Figure 1 and 2 are very small and it is really hard to see how the solutions differ, except for gross patterns.

What is the rationale for presenting barotropic tidal results? There is some improvements with the increase in resolution, but they are relatively small and not significantly better in the 1/32. Furthermore, since you are not using any drag in the 1/32, how is the RMSE of the barotropic tides when compared to TPXO? How does it compare to the barotropic simulation?

Can you provide a quantitative measure of “your belief that the global tide accuracy is reasonable” (line 230)?

Line 268 – The MOIST data are significantly weaker than the model. How does it compare to other published tidal global models or in-situ observations? This needs to be better quantified, even if the difference cannot be fully explained with the current set of experiments.

Line 296: Showing figures with more “textures” is not very informative. Can you quantify how the internal tides signature affect the specific locations and why? How were the three locations chosen? I presume it is because of different surface internal tide signature, but this would benefit from a thorough discussion of how the internal tides modify the spectra at each location. BTW, location of site C is not shown in Figure 9a.

Minor comments:

Why do you have a maximum depth of 7000 m in the tidal simulation and only 5500 m in the non-tidal simulation?
Citation: https://doi.org/10.5194/gmd-2022-52-RC2
RC3: 'Comment on gmd-2022-52', Anonymous Referee #3, 03 May 2022

This manuscript describes the implementation and initial results of simulations using a very high-resolution (1/32°) global ocean model, including waves and tides. This is an exceptional effort and adds to a small handful of similar very high-resolution simulations of the ocean which have been undertaken to date. The paper describes the results of including “mixing from non-breaking waves”, and from the (surface) tides, which in turn generate internal tides. There is clearly merit in publishing some of the results, particularly those describing the tides and internal tides and their implications for comparisons with satellite spectra (i.e. the internal tides induce significant surface variability, leading to better agreement with satellite observations in regions of otherwise low variability), but I think a major revision would be needed first. This would be to address concerns about the “mixing from non-breaking waves”, and also to include some further analysis to look at the evolution of the deeper ocean.

The main difficulty with the paper is the inclusion of the Bv mixing term and referring to this as “mixing by non-breaking waves”, as I do not think that Bv represents such mixing. While the theory is discussed in Qiao et al. (2004), it is simpler to refer to Qiao et al. (2010, Ocean Dynamics 60: 1339-1355), in which a single monochromatic wave is considered in section 2.5. Prandtl theory stipulates that a diffusivity or vertical mixing rate can be specified from the wave average of the vertical velocity perturbation (w’) and some mixing length based on the vertical displacement (l’) of a fluid particle via the formulation <w’l’>, which is defined to be Bv in equation 35 (using slightly different nomenclature). They then choose l’ (below equation 35, their l_3w)) as the orbital vertical excursion due to the wave. It is clear that in this case, for instance, the vertical velocity will be a maximum when the particle is at its mean position (l’=0), and w’ will be zero when the particle is at its maximum vertical position, etc. That is, w’ and l’ are 90° out of phase, or in quadrature, so that <w’l’> = 0. This would actually result from taking the w’ as the vertical component of the wave orbital velocity as specified in their equation 34 (their u_3w), in which an “i” imposes a 90° shift as compared with l’. Instead, the choice (between equations 34 and 35) is made to take w’ to be directly proportional to, and in phase with, l’, so that the resulting average <w’l’> is NON-zero. This choice is difficult to understand and means that Bv will represent an arbitrary mixing term which adds a potentially significant amount of mixing to the ocean near-surface, but which does not represent mixing by non-breaking waves.

Therefore, the paper should remove all reference to Bv as a mixing term due to “non-breaking waves”. Ideally EXP2 should be re-run without the inclusion of Bv. If this is not possible, EXP2 could be used by simply saying that this includes “Bv as a mixing term”, but without referring to this as being “mixing by non-breaking waves”. In particular, the phrase “mixing by non-breaking waves” should not be included anywhere in this paper. In this context, I suggest that Equation 1 should be removed, and also those parts of Figure 7 which show the differences due to Bv (panels(c), (e) and the green line in panel (f)), as this appears to be an unphysical mixing term. Continuing to refer to Bv as “mixing by non-breaking waves” in papers such as this one will only serve to increase the confusion and misunderstanding over this term in the ocean modelling community.

On the other hand, I would like to see a more complete analysis of the behaviour of the model. In particular, it would be important to see how good the model is for purposes of climate modelling, for which the maintenance of a reasonably stable inventory of water masses is needed, or that the model should not drift too quickly from the initial conditions. I suggest the paper therefore include plots to show how the deeper water masses are drifting, and include figures showing the globally-averaged Temperature and Salinity (T and S) anomalies (differences from initial conditions) versus depth and time, also zonally-averaged (or sections at say 40°W and in middle of Pacific) T and S versus depth and latitude at the end of the runs.

It would also be good to include a discussion about how the model scales on various numbers of processors e.g. a figure showing the run time for 1 year of simulation on various numbers of cores, if this is possible.

Further Comments

The English is readable but would benefit from being checked by a native English speaker (e.g. in the Abstract alone in l.s 19, 23, etc).

l. 12 etc. FIO-COM is not a “fully coupled” or even a “coupled” surface wave-tide-circulation model (as claimed several times e.g. l. 12, l. 321) as the waves are being run offline and fed into the tide-circulation model. There is no coupling back from the ocean circulation (or tides) onto the wave field. These claims need to be moderated.

ls. 140-142: what are the barotropic and baroclinic experiments referred to here?

ls. 162-164: was the viscosity higher in the 1/10° model than in the 1/32° model or the same (this is relevant for the EKE discussion, as it is usual to reduce the viscosity at higher resolution as more of the eddies are resolved).

Fig. 1d. The caption should state that this is the globally-averaged EKE.

ls. 188-190. Why is the 1/32° model EKE higher than in the satellite observations in Fig. 1d? Is this because the model can resolve the internal tides but the satellites do not have sufficient resolution to do so? What is the along-track resolution of the satellites, for instance?

Fig. 2. Titles on the subplots (a) and (b) says CMMES – this should be CMEMS.

ls. 213-222. This is mostly a description of the barotropic model set-up and it would be better to discuss this in section 2 (Model description) rather than here in the Results section.

ls. 233-240 and Fig. 6. It is not clear if the model results in panels (c) and (d) show the ¼° model as implied by the text, or the 1/32° model as implied by the figure caption.

Fig. 8. Caption to say that these are internal tide amplitudes at the surface.

Fig. 8. The internal tides in EXP2 are more energetic than in the MOIST observations. This implies that the dissipation of the internal tides is not being properly handled. Please comment on this. Has any explicit dissipation been applied to the internal tides to reduce their propagation?

Fig. 9. Add lines to panels (d) to (f) to show the 70-250 km wave number band referred to in the text (e.g. l. 279).

Fig. 9. Colour bar for panels (a) to (c) should show negative values i.e. from 0 to -5.4 (rather than from 0 to +5.4).

l.321 and elsewhere. The FIO-COM model is NOT fully coupled as the waves are run offline and fed into the tide-circulation model.

Citation: https://doi.org/10.5194/gmd-2022-52-RC3
AC1: 'Comment on gmd-2022-52', Fangli Qiao, 21 Jun 2022

The comment was uploaded in the form of a supplement.

Citation: https://doi.org/10.5194/gmd-2022-52-AC1

Status: closed

RC1: 'Comment on gmd-2022-52', Baylor Fox-Kemper, 07 Apr 2022

The paper "The development and validation of a global 1/32° surface wave-tide-circulation coupled ocean model: FIO-COM32" by Bin Xiao et al. describes the initial stages of developing a 1/32 degree version of the FIO model. Based on past successes of the FIO models, the Bv scheme is prominently discussed, as is the incorporation of tides. The paper focusses on the last year of two 2-3-year simulations EXP1, not including tides or Bv waves, and EXP2 including both. Two other important simulations are noted for future work.

In general, the paper describes a milestone of expensive work in progress, and for this reason many aspects of incomplete experimental design may be overlooked. However, some important theoretical aspects of the work are not mentioned (although they are relevant) and some additional analysis would be informative. Here is my short list of these issues:

1) In the mesoscale 1/10 degree model, wave effects on currents (WEC) and current effects on waves (CEW) are not expected to be very strong. However, as shown in McWilliams & Fox-Kemper (2013: http://dx.doi.org/10.1017/jfm.2013.348) and Suzuki et al. (2016: http://dx.doi.org/10.1002/2015JC011566) the expected magnitude of the WEC effects can be estimated using the epsilon parameter. Given the interest of FIO modeling to include wave impacts in their modeling family, it would be very interesting to see the epsilon parameter estimated in the MASNUM-1/10 and MASNUM-1/32 models.

2) It is not mentioned whether the EXP1 or EXP2 currents refract/diffract/affect the waves in the 1/32 models. It is well known from operational wave modeling that these effects become important roughly in the 1/10 resolution range. They are very important at 1/32 degree resolution. Some estimate of these effects would strengthen this work and provide impetus for a coupled wave-ocean simulation at this resolution to come.

3) Given the offline MASNUM calculation, rather than the directly coupled MASNUM-1/32, it is probably impossible to include both the WEC and CEW effects in the model. However, points 1&2 would show the need for such improvements. This is more interesting than the Bv parameterization result, which shows that small-scale turbulence parameterizations still affect simulations at this resolution. That is not surprising, given that those small-scale turbulence remain far below the resolution at 1/10, 1/32, and even 1/300 degree resolutions. What is more interesting as wave effects over the range of scales from 1/10 to 1/32 is the wave-current coupling.

A) Aside from waves, the new information here primarily results from inclusion of tides. It is an interesting result that tides are significantly improved in the 1/32 degree over 1/10 degree model. However, most of the key metrics discuss only the coherent tides (e.g., Fig 5). As 1/32 degree current calculations could interact much more strongly with tides than the 1/10 degree model, some mention of enhanced incoherent tides would be interesting (and found from a straightforward comparison between EXP1 and EXP2).

B) There is no discussion of the subgrid damping used and how it scales with resolution. Furthermore, a power spectrum showing the rotational and divergent power spectra contributions would be extremely valuable in understanding how the 1/10 and 1/32 models differ at small scales. This information together with more information about the damping would be valuable in understanding the choices made and their consquences, as well as the effective resolution of the vortical and wave/tide modes. This could supplement Fig 9 in a meaningful way, revealing more of the dynamics underpinning the better match of EXP2 to Jason than EXP1.

i) For a submesoscale-permitting model, it would be nice to see what submesoscales are expected to be permitted at 1/32 resolution. The stronger submesoscales in wintertime are now customary, but the weaker submesoscales in summer may be illustrating the limits of 1/32 resolution. It would be nice to include a discussion of Dong et al. (2020: http://dx.doi.org/10.1175/JPO-D-20-0043.1), along with some estimation from the MLD analysis as to the scale of submesoscale baroclinic instabilities. It would be particularly interesting to know if the Bv scheme deepens the MLD or mixes the stratification of the ML enough to have a detectable effect on MLI scale and whether it is more resolvable using Bv. Dong et al. has a similar analysis comparing MLI scales under different boundary layer schemes.

Citation: https://doi.org/10.5194/gmd-2022-52-RC1
RC2:
'Comment on gmd-2022-52', Anonymous Referee #2, 19 Apr 2022
This paper summarizes two high-resolution experiments at 1/32 degree with and without tides. The simulations are spun up for 3 years and diagnostics are performed over the last two years.

This is a major computational exercise and the results are worth documenting. However, as presented, most of the results are expected and in agreement with previous studies. Perhaps the most novel result is the outcome of adding tides which leads to a better agreement between satellite-measured and modeled power spectra. It is indeed nice to see that an increase in resolution leads to a better distribution and a higher magnitude of EKE, but for this paper to be publishable, it needs to go beyond a simple show and tell and provide new insights by performing more in depth analysis of the results and differences.

Specifically,

What does 1/32 gives you in terms of which physical processes are better resolved? It is probably marginal in terms of the submesoscale, so do you see a difference in mixed layer instabilities between 1/10 and 1/32? Is the increase of EKE because of a stronger mesoscale field (lower viscosity) or the addition of submesoscale features?

You allow for only one year spin up from the data assimilative 1/10 run. Is the KE in steady state? Is it sufficient for a mechanical adjustment?

What is the T and S bias after 3 years? You do not use any relaxation to surface salinity which is known to lead to a significant drift in salinity. Can this be quantified? This may not be the main focus of the paper, but it is of importance as it impacts the 3D T and S distribution and strength of the western boundary currents.

This is more of a comment. You use relative wind which is known to have an eddy killing effect (Renault et al., 2019). This is reflected in a modeled EKE is lower than the smooth satellite observed geostrophic EKE.

Line 62: What do you mean by “it is necessary to validate the effect of Bv”? What is the exact question being answered here? Is Bv still effective at 1/32? Do you have any reason what it should not? Is the impact of adding of Bv at 1/10 similar to that of 1/32? Is the mixed layer physic responding differently at 1/10 versus 1/32 (in other word, what is the impact on the MLD of resolving smaller oceanic features?)?

Snapshots are not representative of a solution. Improvements in western boundary current separation, extent and EKE need to be quantified by comparison to observations, not just stating that they qualitatively look better. Figure 1 and 2 are very small and it is really hard to see how the solutions differ, except for gross patterns.

What is the rationale for presenting barotropic tidal results? There is some improvements with the increase in resolution, but they are relatively small and not significantly better in the 1/32. Furthermore, since you are not using any drag in the 1/32, how is the RMSE of the barotropic tides when compared to TPXO? How does it compare to the barotropic simulation?

Can you provide a quantitative measure of “your belief that the global tide accuracy is reasonable” (line 230)?

Line 268 – The MOIST data are significantly weaker than the model. How does it compare to other published tidal global models or in-situ observations? This needs to be better quantified, even if the difference cannot be fully explained with the current set of experiments.

Line 296: Showing figures with more “textures” is not very informative. Can you quantify how the internal tides signature affect the specific locations and why? How were the three locations chosen? I presume it is because of different surface internal tide signature, but this would benefit from a thorough discussion of how the internal tides modify the spectra at each location. BTW, location of site C is not shown in Figure 9a.

Minor comments:

Why do you have a maximum depth of 7000 m in the tidal simulation and only 5500 m in the non-tidal simulation?
Citation: https://doi.org/10.5194/gmd-2022-52-RC2
RC3: 'Comment on gmd-2022-52', Anonymous Referee #3, 03 May 2022

This manuscript describes the implementation and initial results of simulations using a very high-resolution (1/32°) global ocean model, including waves and tides. This is an exceptional effort and adds to a small handful of similar very high-resolution simulations of the ocean which have been undertaken to date. The paper describes the results of including “mixing from non-breaking waves”, and from the (surface) tides, which in turn generate internal tides. There is clearly merit in publishing some of the results, particularly those describing the tides and internal tides and their implications for comparisons with satellite spectra (i.e. the internal tides induce significant surface variability, leading to better agreement with satellite observations in regions of otherwise low variability), but I think a major revision would be needed first. This would be to address concerns about the “mixing from non-breaking waves”, and also to include some further analysis to look at the evolution of the deeper ocean.

The main difficulty with the paper is the inclusion of the Bv mixing term and referring to this as “mixing by non-breaking waves”, as I do not think that Bv represents such mixing. While the theory is discussed in Qiao et al. (2004), it is simpler to refer to Qiao et al. (2010, Ocean Dynamics 60: 1339-1355), in which a single monochromatic wave is considered in section 2.5. Prandtl theory stipulates that a diffusivity or vertical mixing rate can be specified from the wave average of the vertical velocity perturbation (w’) and some mixing length based on the vertical displacement (l’) of a fluid particle via the formulation <w’l’>, which is defined to be Bv in equation 35 (using slightly different nomenclature). They then choose l’ (below equation 35, their l_3w)) as the orbital vertical excursion due to the wave. It is clear that in this case, for instance, the vertical velocity will be a maximum when the particle is at its mean position (l’=0), and w’ will be zero when the particle is at its maximum vertical position, etc. That is, w’ and l’ are 90° out of phase, or in quadrature, so that <w’l’> = 0. This would actually result from taking the w’ as the vertical component of the wave orbital velocity as specified in their equation 34 (their u_3w), in which an “i” imposes a 90° shift as compared with l’. Instead, the choice (between equations 34 and 35) is made to take w’ to be directly proportional to, and in phase with, l’, so that the resulting average <w’l’> is NON-zero. This choice is difficult to understand and means that Bv will represent an arbitrary mixing term which adds a potentially significant amount of mixing to the ocean near-surface, but which does not represent mixing by non-breaking waves.

Therefore, the paper should remove all reference to Bv as a mixing term due to “non-breaking waves”. Ideally EXP2 should be re-run without the inclusion of Bv. If this is not possible, EXP2 could be used by simply saying that this includes “Bv as a mixing term”, but without referring to this as being “mixing by non-breaking waves”. In particular, the phrase “mixing by non-breaking waves” should not be included anywhere in this paper. In this context, I suggest that Equation 1 should be removed, and also those parts of Figure 7 which show the differences due to Bv (panels(c), (e) and the green line in panel (f)), as this appears to be an unphysical mixing term. Continuing to refer to Bv as “mixing by non-breaking waves” in papers such as this one will only serve to increase the confusion and misunderstanding over this term in the ocean modelling community.

On the other hand, I would like to see a more complete analysis of the behaviour of the model. In particular, it would be important to see how good the model is for purposes of climate modelling, for which the maintenance of a reasonably stable inventory of water masses is needed, or that the model should not drift too quickly from the initial conditions. I suggest the paper therefore include plots to show how the deeper water masses are drifting, and include figures showing the globally-averaged Temperature and Salinity (T and S) anomalies (differences from initial conditions) versus depth and time, also zonally-averaged (or sections at say 40°W and in middle of Pacific) T and S versus depth and latitude at the end of the runs.

It would also be good to include a discussion about how the model scales on various numbers of processors e.g. a figure showing the run time for 1 year of simulation on various numbers of cores, if this is possible.

Further Comments

The English is readable but would benefit from being checked by a native English speaker (e.g. in the Abstract alone in l.s 19, 23, etc).

l. 12 etc. FIO-COM is not a “fully coupled” or even a “coupled” surface wave-tide-circulation model (as claimed several times e.g. l. 12, l. 321) as the waves are being run offline and fed into the tide-circulation model. There is no coupling back from the ocean circulation (or tides) onto the wave field. These claims need to be moderated.

ls. 140-142: what are the barotropic and baroclinic experiments referred to here?

ls. 162-164: was the viscosity higher in the 1/10° model than in the 1/32° model or the same (this is relevant for the EKE discussion, as it is usual to reduce the viscosity at higher resolution as more of the eddies are resolved).

Fig. 1d. The caption should state that this is the globally-averaged EKE.

ls. 188-190. Why is the 1/32° model EKE higher than in the satellite observations in Fig. 1d? Is this because the model can resolve the internal tides but the satellites do not have sufficient resolution to do so? What is the along-track resolution of the satellites, for instance?

Fig. 2. Titles on the subplots (a) and (b) says CMMES – this should be CMEMS.

ls. 213-222. This is mostly a description of the barotropic model set-up and it would be better to discuss this in section 2 (Model description) rather than here in the Results section.

ls. 233-240 and Fig. 6. It is not clear if the model results in panels (c) and (d) show the ¼° model as implied by the text, or the 1/32° model as implied by the figure caption.

Fig. 8. Caption to say that these are internal tide amplitudes at the surface.

Fig. 8. The internal tides in EXP2 are more energetic than in the MOIST observations. This implies that the dissipation of the internal tides is not being properly handled. Please comment on this. Has any explicit dissipation been applied to the internal tides to reduce their propagation?

Fig. 9. Add lines to panels (d) to (f) to show the 70-250 km wave number band referred to in the text (e.g. l. 279).

Fig. 9. Colour bar for panels (a) to (c) should show negative values i.e. from 0 to -5.4 (rather than from 0 to +5.4).

l.321 and elsewhere. The FIO-COM model is NOT fully coupled as the waves are run offline and fed into the tide-circulation model.

Citation: https://doi.org/10.5194/gmd-2022-52-RC3
AC1: 'Comment on gmd-2022-52', Fangli Qiao, 21 Jun 2022

The comment was uploaded in the form of a supplement.

Citation: https://doi.org/10.5194/gmd-2022-52-AC1

Bin Xiao et al.

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Short summary

A new global surface wave-tide-circulation coupled ocean model FIO-COM32 with resolution of 1/32° × 1/32° is developed and validated. Both the promotion of the horizontal resolution and included physical processes are proved to be important contributors to the significant improvements of FIO-COM32 simulations. It should be the time to merge these separated model components (surface wave, tidal current and ocean circulation) for new generation ocean model development.


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