the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
An Improved Parameterization of Sea Spray-Mediated Heat Flux Using Gaussian Quadrature: Case Studies with a Coupled CFSv2.0-WW3 System
Ruizi Shi
Fanghua Xu
Abstract. Sea spray-mediated heat flux plays an important role in air-sea heat transfer. Heat flux integrated over droplet size spectrum can well simulate total heat flux induced by sea spray droplets. Previously, a fast spray-flux scheme assuming single-radius droplets (A15) was widely used since the full-size spectrum integral is computational expensive. Based on the Gaussian Quadrature (GQ) method, a new fast scheme (SPRAY-GQ) of sea spray-mediated heat flux is derived. The performance of SPRAY-GQ is evaluated by comparing heat fluxes with those estimated from the widely-used A15. The new scheme shows a better agreement with the original spectrum integral. To further evaluate the performance of A15 and SPRAY-GQ, the two schemes are implemented into a coupled CFSv2.0-WW3 system, and a series of 56-day simulations in summer and winter are conducted and compared. The comparisons with satellite measurements and reanalysis data show that the SPRAY-GQ scheme could simulate air-sea heat flux more reasonably than the A15 scheme. For experiments based on SPRAY-GQ, the sea surface temperature at mid-high latitudes of both hemispheres, particularly in summer, is significantly improved compared with the experiments based on A15. The simulation of 10-m wind speed and significant wave height at mid-low latitudes of the Northern Hemisphere is improved as well. The computational time of SPRAY-GQ is about the same as that of A15. Thereby, the newly-developed SPRAY-GQ scheme has a potential to be used for improving air-sea heat flux in coupled models.
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Ruizi Shi and Fanghua Xu
Status: closed
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RC1: 'Comment on gmd-2022-233', Anonymous Referee #1, 14 Dec 2022
The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2022-233/gmd-2022-233-RC1-supplement.pdf
- AC1: 'Reply on RC1', Ruizi Shi, 04 Jan 2023
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RC2: 'Comment on gmd-2022-233', Anonymous Referee #2, 16 Dec 2022
The authors present a new numerical method to calculate sea spray induced heat fluxes given a sea spray generation function. Specifically, the authors propose the Gaussian Quadrature (GQ) method as a computationally efficient alternative to the spectrum integral method, and more accurate method than simplifications of the integral method. The results show improved agreement of the GQ method with the spectrum integral in comparison to the simplified parameterization. Impact of such difference in the context of world’s oceans are presented using a coupled ocean-atmospheric-wave model.
Overall, the manuscript is interesting and the modelling community may benefit significantly from the proposed GQ-method. However, the authors are not clear in the type of advancement and implications their work has on current and future works. The method does not improve the physics of sea spray induced heat fluxes, instead it improves the numerical accuracy of solving the involved equations. While I nevertheless believe this is important work worthy to be published, it is an important distinction that is currently not appropriately phrased nor discussed. I therefore recommend a major revision.
Major concerns
- As per the above, I believe that the authors need to be more explicit in what their method is improving. I think that the authors haven’t necessarily overstated their conclusions, but the interpretations of some statements are right now too ambiguous or sometimes incorrect. This largely involves the word ‘improved’ throughout the manuscript, including the title and abstract, where it reads as if the parameterizations are improved. This is not really true, it is actually the numerical method used to solve the parameterizations that has been improved (at least against the simplified parameterization discussed in the manuscript). Thus, when these different methods are compared when implemented in the applied coupled model, the authors are not improving the bulk parameterizations, but simply presenting the numerical error of the methods discussed in the context of the coupled model. Importantly, it is the numerical error assuming that the sea spray generation function is correct.
- A related point is the absence of a clear discussion on the interpretation of the results. As mentioned by the authors, the sea spray generation function has an uncertainty of several orders of magnitude. Thus, if the RMSE of the proposed GQ method reduces the numerical error by say 1-10 W/m2 (e.g., figs 3-5), how relevant is such an improvement in the broader context of the physics and model uncertainty? Such uncertainty in the physics could perhaps get into the 100s of W/m2. I’m not suggesting the GQ method proposed here is therefore irrelevant, but it does change the interpretation and application of the model/results in practice, for now and the future. This also brings up some other questions regarding the interpretation of the improved SST as observed in Figs 6 and 7. The uncertainty in the physics of sea spray is considerable larger than the improvement in approximating the spectral integral using the GQ method. Thus, any improvements in the modelled SST cannot be reliably be assigned to the usage of the GQ method.
Minor comments:
- Line 66: ‘huge amount’ sounds a bit vague. Especially later on the authors actually provide a number, so they can be more accurate here.
- Line 70: ‘apt to produce significant bias’, more a numerical error. However, as per one of my major concerns, is this bias/error of significance in the context of the existing uncertainty in sea spray parameterizations?
- Line 86: ‘thus provided reliable hourly estimates’, is very vague. Either provide a reference about its reliability, or simply state that this dataset is used.
- Line 100: This sentence reads a bit odd. ‘based on eddy correlation observations’ refers to the turbulent heat fluxes in cited papers, not the sea spray induced heat flux.
- Line 108: ‘requires huge amount’, just say is computationally expensive
- Line 123-124: somewhat confusing, please rephrase sentence
- 166: ’36 times’ this is an interesting and useful statistic. Perhaps consider to provide what this means in terms of the fully coupled model run, i.e., is it still saving much time percentage wise?
- Line 201-202: confusing sentence, please repharse
- Line 204: ‘fig 12g’ best practice is to keep order of figures intact.
- Line 233: ‘significant improvements’, I disagree. Fig. 8c and 9c seem to show very similar RMSE. Their variability after day 18 is very similar.
- Line 260: This manuscript would greatly benefit from a separate and in-depth discussion on the interpretation and implications of the results.
Citation: https://doi.org/10.5194/gmd-2022-233-RC2 -
AC2: 'Reply on RC2', Ruizi Shi, 04 Jan 2023
We sincerely appreciate the reviewer for her/his constructive comments on the manuscript. Our responses are attached.
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RC3: 'Reply on AC2', Anonymous Referee #2, 09 Jan 2023
The authors have addressed my concerns. While the added paragraph is not really a discussion of the results, more a summary/conclusion, I do think it clarifes my concerns sufficiently. Thus, after these edits I think it is suitable for publication.
Citation: https://doi.org/10.5194/gmd-2022-233-RC3 -
AC3: 'Reply on RC3', Ruizi Shi, 10 Jan 2023
Thank you very much for your time and your encouraging comments. We will upload the revised text soon.
Citation: https://doi.org/10.5194/gmd-2022-233-AC3
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AC3: 'Reply on RC3', Ruizi Shi, 10 Jan 2023
-
RC3: 'Reply on AC2', Anonymous Referee #2, 09 Jan 2023
Status: closed
-
RC1: 'Comment on gmd-2022-233', Anonymous Referee #1, 14 Dec 2022
The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2022-233/gmd-2022-233-RC1-supplement.pdf
- AC1: 'Reply on RC1', Ruizi Shi, 04 Jan 2023
-
RC2: 'Comment on gmd-2022-233', Anonymous Referee #2, 16 Dec 2022
The authors present a new numerical method to calculate sea spray induced heat fluxes given a sea spray generation function. Specifically, the authors propose the Gaussian Quadrature (GQ) method as a computationally efficient alternative to the spectrum integral method, and more accurate method than simplifications of the integral method. The results show improved agreement of the GQ method with the spectrum integral in comparison to the simplified parameterization. Impact of such difference in the context of world’s oceans are presented using a coupled ocean-atmospheric-wave model.
Overall, the manuscript is interesting and the modelling community may benefit significantly from the proposed GQ-method. However, the authors are not clear in the type of advancement and implications their work has on current and future works. The method does not improve the physics of sea spray induced heat fluxes, instead it improves the numerical accuracy of solving the involved equations. While I nevertheless believe this is important work worthy to be published, it is an important distinction that is currently not appropriately phrased nor discussed. I therefore recommend a major revision.
Major concerns
- As per the above, I believe that the authors need to be more explicit in what their method is improving. I think that the authors haven’t necessarily overstated their conclusions, but the interpretations of some statements are right now too ambiguous or sometimes incorrect. This largely involves the word ‘improved’ throughout the manuscript, including the title and abstract, where it reads as if the parameterizations are improved. This is not really true, it is actually the numerical method used to solve the parameterizations that has been improved (at least against the simplified parameterization discussed in the manuscript). Thus, when these different methods are compared when implemented in the applied coupled model, the authors are not improving the bulk parameterizations, but simply presenting the numerical error of the methods discussed in the context of the coupled model. Importantly, it is the numerical error assuming that the sea spray generation function is correct.
- A related point is the absence of a clear discussion on the interpretation of the results. As mentioned by the authors, the sea spray generation function has an uncertainty of several orders of magnitude. Thus, if the RMSE of the proposed GQ method reduces the numerical error by say 1-10 W/m2 (e.g., figs 3-5), how relevant is such an improvement in the broader context of the physics and model uncertainty? Such uncertainty in the physics could perhaps get into the 100s of W/m2. I’m not suggesting the GQ method proposed here is therefore irrelevant, but it does change the interpretation and application of the model/results in practice, for now and the future. This also brings up some other questions regarding the interpretation of the improved SST as observed in Figs 6 and 7. The uncertainty in the physics of sea spray is considerable larger than the improvement in approximating the spectral integral using the GQ method. Thus, any improvements in the modelled SST cannot be reliably be assigned to the usage of the GQ method.
Minor comments:
- Line 66: ‘huge amount’ sounds a bit vague. Especially later on the authors actually provide a number, so they can be more accurate here.
- Line 70: ‘apt to produce significant bias’, more a numerical error. However, as per one of my major concerns, is this bias/error of significance in the context of the existing uncertainty in sea spray parameterizations?
- Line 86: ‘thus provided reliable hourly estimates’, is very vague. Either provide a reference about its reliability, or simply state that this dataset is used.
- Line 100: This sentence reads a bit odd. ‘based on eddy correlation observations’ refers to the turbulent heat fluxes in cited papers, not the sea spray induced heat flux.
- Line 108: ‘requires huge amount’, just say is computationally expensive
- Line 123-124: somewhat confusing, please rephrase sentence
- 166: ’36 times’ this is an interesting and useful statistic. Perhaps consider to provide what this means in terms of the fully coupled model run, i.e., is it still saving much time percentage wise?
- Line 201-202: confusing sentence, please repharse
- Line 204: ‘fig 12g’ best practice is to keep order of figures intact.
- Line 233: ‘significant improvements’, I disagree. Fig. 8c and 9c seem to show very similar RMSE. Their variability after day 18 is very similar.
- Line 260: This manuscript would greatly benefit from a separate and in-depth discussion on the interpretation and implications of the results.
Citation: https://doi.org/10.5194/gmd-2022-233-RC2 -
AC2: 'Reply on RC2', Ruizi Shi, 04 Jan 2023
We sincerely appreciate the reviewer for her/his constructive comments on the manuscript. Our responses are attached.
-
RC3: 'Reply on AC2', Anonymous Referee #2, 09 Jan 2023
The authors have addressed my concerns. While the added paragraph is not really a discussion of the results, more a summary/conclusion, I do think it clarifes my concerns sufficiently. Thus, after these edits I think it is suitable for publication.
Citation: https://doi.org/10.5194/gmd-2022-233-RC3 -
AC3: 'Reply on RC3', Ruizi Shi, 10 Jan 2023
Thank you very much for your time and your encouraging comments. We will upload the revised text soon.
Citation: https://doi.org/10.5194/gmd-2022-233-AC3
-
AC3: 'Reply on RC3', Ruizi Shi, 10 Jan 2023
-
RC3: 'Reply on AC2', Anonymous Referee #2, 09 Jan 2023
Ruizi Shi and Fanghua Xu
Ruizi Shi and Fanghua Xu
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