the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jan 2025
M2 Monthly and annual mode 1 and mode 2 internal tide atlases from altimetry data and MIOST: focus on the Indo-Philippine Archipelago and the region off the Amazon shelf
Abstract. The M2 MIOST24 (Multivariate Inversion of Ocean Surface Topography 2024) internal tide atlases are available in annual (MIOST24a) and monthly (MIOST24m) regional versions for modes 1 and 2 in the Indo-Philippine archipelago and the region off the Amazon shelf. They are derived from 25 years (1993–2017, period 1) of sea level anomalies (SLA) from altimetry observations. Compared to MIOST22, MIOST24 incorporates M2 modes 1 and 2 wavelengths based on monthly stratification profiles from GLORYS12v1 (1993–2020). The differences between MIOST24a and MIOST22a lead to RMSE (Root Mean Square Error) of up to 3 cm, reflecting amplitude changes, while the RMSE between MIOST24a and HRET (High-Resolution Empirical Tide) indicate both amplitude and phase differences. MIOST24m highlights significant monthly variability of M2 internal tides in the Indo-Philippine archipelago and off the Amazon shelf. In the Amazon region, the internal tide propagates far offshore from March to June but is blocked closer to the coast from August to December. For both regions, mode 1 monthly variability is mainly phase-related, while mode 2 is more amplitude-dependent. Variance reductions of SLA show that MIOST24m outperforms MIOST24a, MIOST22a and HRET on period 1 in the two regions of interest, and on the Amazon region in period 2 (2018–2023). Monthly atlases are therefore recommended to correct the internal tides of the SLA used to derive them. All these results support the development of an improved MIOST24 global atlas.
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RC1: 'Comment on egusphere-2024-3947', Anonymous Referee #1, 27 Jan 2025
The authors conducted an assessment of a new dataset on internal tides estimated using satellite altimetry data. While the paper includes limited physical discussions regarding internal tides, it provides a detailed evaluation of sea surface displacement associated with internal tides, making this dataset highly valuable to many oceanographers. Therefore, this paper can be considered worthy of publication in Ocean Science. However, as there are several issues in the current manuscript, as outlined below, it is recommended that these be appropriately revised before publication.
Comments
- On lines 114-115, the authors state that “…, for MIOST22 the wavelength of mode 1 corresponds to the first Rossby deformation radius…”, but I have doubts about this claim. This is because, in constructing the MIOST22 dataset, Ubelmann et al. (2022) estimated the phase velocity (referred to as “Cp” in equation 12 of Ubelmann et al. (2022)) using a method similar to the one in this manuscript. Equation (1) of this manuscript and equation (12) of Ubelmann et al. (2022) are apparently identical when considering Cp=ωλn/2π. Also, for the first baroclinic-mode phase speed (referred to as “Cn” in this manuscript and as “c” in Ubelmann et al. (2022)), Ubelmann et al. (2022) used Chelton et al.’s (1998) dataset, which is estimated through the WKB method (equation 2.2 of Chelton et al. (1998)). The WKB method provides a solution close to that of the eigenvalue problem method used in this manuscript (Chelton et al., 1998). Considering the above, the statement that “for MIOST22 the wavelength of mode 1 corresponds to the first Rossby deformation radius” appears to be incorrect. This is a crucial point in the motivation of this study, so I would appreciate an accurate response.
- The figure caption in Fig. 6 may have a typo: “Avril” should be “April.”
Citation: https://doi.org/10.5194/egusphere-2024-3947-RC1 -
RC2: 'Comment on egusphere-2024-3947', Anonymous Referee #2, 13 Feb 2025
Review of
"M2 Monthly and annual mode 1 and mode 2 internal tide atlases from altimetry
data and MIOST: focus on the Indo-Philippine Archipelago and the region off the
Amazon shelf"
by Tchilibou et al
This manuscripts describes the development of empirical internal tide models
with monthly temporal resolution for two regions, the Indo-Philippine
archipelago and the Amazon shelf region. Seasonal variability of the
internal tides has previously been identified in both of these
regions, so they make good test cases for the proposed strategy.New versions of the MIOST internal tide model are introduced which differ
from previous work in two respects: (1) the internal tide wavelength
parameters are computed more accurately and from an ocean reanalysis
product, and (2) the tides are estimated within monthly windows (the
tide within each month as determined by fitting over 25 years of data).The results involve comparisons of the new MIOST models with the previous
MIOST and HRET models. The results are discussed with approriate nuance
and detail. Also, the authors do a good job of contrasting between the
"goodness-of-fit" (comparison to data used to build the models in Period 1)
and the "variance reduction" (comparison to withheld data in Period 2).
Furthermore, the duration of Period 2 is long enough that it should be
capable of identifying significant differences in explained variance.Because the results show significant increases in variance reduction
during Period 2, I think this article will be of interest to many readers
and it ought to inform the further development of global internal tide atlases
with monthly resolution. Therefore, I think the article should be
accepted for publication. I list a few detailed comments, below, but I think
these can all be handled at the proofreading stage. I don't think the
article needs a second review.
Detailed comments:Abstract:
L16: What is MIOST22?L27: What is implied by "improved"? Say, "at monthly resolution", if that is
what is meant.L33: comma or not after "et al."?
L36: comma before Desai. Are these lists of citations formatted correctly?
I would recommend a semicolon between citations.L37-38: "Zaron (2019)" not "Zaron et al (2019)"
L80: "wavelengths' bases" --> "assumed wavelengths"?
L73-L75: here and throughout: I cannot see a pattern in the ordering of multiple citations. Please use a pattern such as chronological, alphabetical, etc.
L72-L83: This paragraph should mention the work of Kaur:
https://os.copernicus.org/articles/20/1187/2024/L86-L88: fix left margin
L117: Is there a reason why the rigid lid condition was used at the upper
boundary? I think Wunsch JTech 2013 discusses sensitivity to this assumption.L129: The monthly standard deviations appear to be miniscule, no more than
5% of the mean in the deep water where modes 1 and 2 could conceivably
be identified. Is this variability found to be significant?L190: This is very good that you used a long data window for validation,
sufficient to distinguish the major tides.L193-L203: This paragraph makes it clear that the monthly atlas contains
a tidal estimate for each calendar month, averaged ofer the 25 years of the
Period 1 dataset. Prior to this paragraph, I misunderstood and thought that
the monthly estimates were provided for each and every month in Period 1.
This is a difficult distinction to communicate, but I think it is important
enough that it should somehow me made earlier in the text. Also, if I am
understanding correctly, the monthly harmonic constants are, in fact,
phase-locked or stationary (since they are obtained from the average months
over 25 years data). This distinction should also be made.L274: "Avril" --> "April"
Fig 6 and Fig 7: These figures are too small and I would like to see more
detail. Please use 2-columns max for these.Fig 8b: Increase size of legend text.
Fig 8 and L286-L294: Instead of using RMSE, maybe you could refer
to it as RMSD, since you have
not made a definition of what is "error" vs a simple "difference".Fig 11: These are nice summary figures. The text also does a good job
of distinguishing the performance of the models during Period 1
and Period 2, where it is the latter which is the real test period.Citation: https://doi.org/10.5194/egusphere-2024-3947-RC2
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