Improved Estimates of Geocenter Variability from Time-Variable Gravity and Ocean Model Outputs
Don Chambers
Round 1
Reviewer 1 Report
This is a very nice study updating geocenter estimates using GRACE and ocean models by including self-gravitation and loading (SAL) effects to the ocean mass fluctuations instead of assuming a uniform fluctuation. The authors present results from a well-designed simulation to demonstrate the improvement in accuracy of the recovered geocenter, then apply to real GRACE measurements. They also comment on effects of utilizing different GIA models, ocean models, and atmospheric model. I have to admit, I was expecting more of a difference between the SAL-corrected model and the static model. While the 0.2-0.3 mm in annual amplitude and trend differences < 0.05 mm/year may be statistically significant, they're a lot smaller than I expected -- and a little gratifying to see considering I am a co-author on the Swenson et al study.
Overall, the manuscript is very nearly publishable as is. I do have just a few minor comments, mainly regarding clarification of the statistical basis for the uncertainties quoted.
Section 4.3, Uncertainty estimates: are these values based on RMS error as in Section 4.1, or another statistic (i.e., standard deviation, one standard error, etc)? Can the authors also discuss differences in amplitude and phase of the annual fits (i.e., results shown in Tables 1 and 2). Which are statistically different? Trend differences are discussed extensively, but not the seasonal. What does the uncertainty on the best fits represent? Is it standard error? 90% confidence? Are residuals assumed uncorrelated and random, or is serial correlation in the residuals accounted for? It's difficult to quantify the significance of the differences without this basic information.Author Response
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Author Response.pdf
Reviewer 2 Report
Strength: The logic of this manuscript is legitimate and sound. The calculation is done correctly and completely, and the data sets are treated the way they are supposed to be. The writing is good.
Weakness: I cannot say that this manuscript is innovative or really impactful, as it adds little to what we already know. There is no surprise in the outcome of the calculation, which matches the ocean models reasonably well as expected.
On balance, I would recommend its publication in RS as is. Or I could suggest that it be strengthened as to stating why this study is interesting.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The paper presents an improved methodology to estimate geocenter variability based on GRACE and GRACE follow on data and ocean models, also considering the effects of self attraction and loading. The paper is clear and well written, results are well supported by the data and show the goodness of the proposed method. I just have a couple of minor comments:
1) I suggest to increase the size of figures 3, 5, 8 or to plot one time series as a reference and the difference with respect to the reference to improve the readibility.
2) Caption for figure usually should be put just below the figure. Please check the Journal guideline and in case move the captions.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
The authors are using GRACE and GRACE-FO estimates to calculate the Earth's geocenter variability. Overall, the paper is well-written and the topic is interesting. The authors did a great job representing this new enhanced approach in geocenter estimation.
Author Response
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Author Response File: Author Response.pdf
