Evaluation of sub-monthly oceanographic signal in GRACE “daily” swath series using altimetry

Bonin, Jennifer A.; Save, Himanshu

doi:https://doi.org/10.5194/os-16-423-2020

Articles | Volume 16, issue 2

https://doi.org/10.5194/os-16-423-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-16-423-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 2

Research article

|

15 Apr 2020

Research article |

| 15 Apr 2020

Evaluation of sub-monthly oceanographic signal in GRACE “daily” swath series using altimetry

Jennifer A. Bonin and Himanshu Save

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Final revised paper (published on 15 Apr 2020)
Supplement to the final revised paper
Preprint (discussion started on 11 Jul 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review', Henryk Dobslaw, 16 Jul 2019
- AC1: 'Thank you for the review', Jennifer Bonin, 17 Sep 2019
RC2: 'Review', Anonymous Referee #2, 12 Nov 2019
- AC2: 'Thank you for the review', Jennifer Bonin, 20 Dec 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Jennifer Bonin on behalf of the Authors (20 Dec 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Jan 2020) by Joanne Williams

RR by Anonymous Referee #2 (14 Jan 2020)

Suggestions for revision or reasons for rejection

I am satisfied with all the changes the authors made, except for one. My main objection -- to the handling of the altimeter data -- still stands. Rather than modify their handling and the discussion of the supposed inconsistency in Jason data, the authors added to the discussion. Their justification was partly because of the reviewers' "confusion" on the matter (line 285 of Reply). I was not confused.

I'll attempt to be more clear. In my opinion, Figure 1 in its present form is unacceptable. The implied inconsistency between Jason-1 and Jason-2 calls into question much previous work on this topic. I already cited work by Ablain et al. and Beckley et al. There has been other work as well. The figure also calls into question the critical work that has been done on sea level rise. If Jason-1 and Jason-2 are as inconsistent as Figure 1 implies, how could there be any credence in the altimeter community's sea level curves? In fact, the only inconsistency here is the authors' use of inconsistent generations of GDRs, when the documentation to those GDRs already notes the inconsistent fields being used (and not just MSS).

I recommend one of the following two approaches:

1. The authors should use altimeter products that have been designed to be as consistent as possible over the T/P and Jason missions. Two possible choices are to use the AVISO/CMEMS or the PODAAC MEASURES products. The authors rejected this recommendation because they didn't wish to use gridded data. In fact, both these projects produce along-track data. CMEMS even produces two varieties: along-track SSH anomalies and along-track absolute dynamic topography. I don't remember what MEASURES produces, probably SSH anomalies. Using these products would ensure the authors are using altimetry that is consistent as is currently possible over the period 1993 to 2019.

2. Stay with what is done now, but change the emphasis and acknowledge this isn't the ideal approach. Rather than attacking the mission project teams for making inconsistent generations of GDRs, the authors should be apologetic for using inconsistent generations. Sentences like:
"Thus our surprise..." should instead read:
"As must be expected..."
Or such sentences can be eliminated entirely, because most of the details of the GDR inconsistencies hardly matter, except to address what has been done by the authors during their own data processing. We certainly don't need the MSS cartoon. We probably don't need Figure 1 either, unless it is to show that after their various adjustments the authors get something similar to previously published work.

The authors argue that Figure 1 and in-depth discussion will save other users from these problems. Hopefully, other users are not doing this. Anyway, I wager that the great majority of oceanographers use either AVISO or MEASURES or RADS, and very few go back to GDRs, in part for reasons the authors have discovered.

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RR by Henryk Dobslaw (23 Jan 2020)

ED: Reconsider after major revisions (23 Jan 2020) by Joanne Williams

AR by Jennifer Bonin on behalf of the Authors (04 Mar 2020) Author's response Manuscript

ED: Publish subject to technical corrections (11 Mar 2020) by Joanne Williams

AR by Jennifer Bonin on behalf of the Authors (18 Mar 2020) Manuscript

Short summary

Bottom pressure estimates from three GRACE gravity series and two global ocean models are compared to Jason altimetry sea level anomaly estimates to determine the accuracy of the GRACE and model data at sub-monthly timescales. The GRACE series can explain 25–75 % of the sub-monthly altimetric variability in most ocean regions with high signal strength. The GRACE series explain more of the sub-monthly variability than their de-aliasing model products can to periods as short as 10 d.