the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Comparison of the H2O, HDO and δD stratospheric climatologies between the MIPAS-ESA v8, MIPAS-IMK v5 and ACE-FTS v4.1/4.2 satellite data sets
Karen De Los Ríos
Paulina Ordoñez
Gabriele P. Stiller
Piera Raspollini
Marco Gai
Kaley A. Walker
Cristina Peña-Ortiz
Abstract. Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H2O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H2O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H2O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6–10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H2O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H2O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of δD are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal δD variations, the results suggest that in the current data versions, the calculated isotopic composition (δD) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological δD composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these δD observations.
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Karen De Los Ríos et al.
Status: open (until 09 Oct 2023)
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CC1: 'Comment on egusphere-2023-1348', Geoff Toon, 30 Aug 2023
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Publisher’s note: this comment is a copy of RC1 and its content was therefore removed.
Citation: https://doi.org/10.5194/egusphere-2023-1348-CC1 -
RC1: 'Comment on egusphere-2023-1348', Geoff Toon, 31 Aug 2023
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General Comments
This paper compares MIPAS and ACE H2O and HDO over the period 2004 to 2012 when MIPAS was working. Similar comparisons have been done previously, such as Lossow et al., 2020, Lossow et al., 2011, Sheese et al., 2017, Ordonez-Perez et al., 2021, Risi et al., 2011, Hogberg 2019. This latest comparison utilizes more recent versions of the data products which are presumably better. Indeed, the authors state " The HDO data version used here differs significantly from the data versions assessed by Lossow et al. (2020) and Högberg et al. (2019) and used by Steinwagner et al. (2007, 2010)". In this latest paper, a new MIPAS product is presented for the first time: MIPAS-ESA. This and MIPAS-IMK are compared with ACE and with each other. It is not clear to me where, in the processing chain, these two MIPAS products diverge. The retrieval methods seem to be different. Not clear whether the spectra are the same.
To be honest, I didn't feel that I learned much reading this paper. There have already been several similar comparisons using earlier versions of the MIPAS and ACE data products. The authors show that the MIPAS-IMK H2O and HDO products agree well with ACE, but the MIPAS-ESA HDO profiles are discrepant around 40 km altitude. Since the error bars on the MIPAS HDO profiles are quite large above 30 km, the discrepancy is not significant.
Line 21 states "Stratospheric H2O and HDO global average coincident profiles reveal good agreement." I disagree. In my opinion a 37.5% bias in HDO at 40 km is not good agreement. Although the MIPAS HDO profiles have large enough uncertainties such that they bridge this 37.5% gap, this doesn't mean that the agreement is good. It just means that the MIPAS HDO measurements are not useful at 40 km and above.
Specific Comments
Lines 24-25 of the abstract state "ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8% and -37.5%, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude" So ACE is 4.8% lower than MIPAS-IMK and 37.5% lower than MIPAS-ESA. One might naively expect MIPAS-IMK HDO to be 37.5-4.8 = 32.7% lower than MIPAS-ESA. But it is only 28.1% lower. Presumably this is because different data were used for comparing ACE with MIPAS, than comparing MIPAS-IMK and MIPAS-ESA. Perhaps this should be made clearer in the text.
Lines 29-30 of the abstract state: " ...aligns more closely with expected stratospheric behavior for the entire stratosphere". Delete "stratospheric" or " for the entire stratosphere" . This is unnecessary to have both. Also, this sentence states that MIPAS-IMK calculates dD. I consider it more of a measurement. A model would calculate dD.
Line 15: I've not seen the word "isotopological" before. According to Google it is a mathematical term meaning "having the same topology". Perhaps the authors mean "isotopic"? Line 29 of the abstract uses "isotopic" in a similar context. The word "isotopological" occurs later in the paper, e.g. lines 54, 56. So I'm not sure if the authors are trying to make a distinction between "isotopological" and "isotopic", or they consider these terms synonymous. I suggest that "isotopological" NOT be used, because mathematicians have already defined this word for use in topology.
Line 54 states: "isotopological composition of WV" change to "isotopic composition of WV"
Line 56 states: "Among the isotopological species of WV..." Change to "Among the isotopologues of WV...".
Having read the paper, what I would really like to know is why MIPAS-IMK and MIPAS-ESA HDO are different. Presumably these products come from the same raw data. It undermines confidence in MIPAS to see different groups obtain such different results.
Example of duplication; Line 25-26: The meridional cross-sections of H2O and HDO exhibit the expected distribution that has been established in previous studies. Lines 27-28: The meridional cross-sections of δD are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. The sentence on lines 27-28 seems superfluous. Given that H2O and HDO are in good agreement with previous datasets and studies, readers will assume that dD will also be in good agreement. No need to tell them that it is.
Raspollini et al., 2022 is cited on lines 86 and 148, but doesn't exist in the References. Either these citations are typos (should be 2020, perhaps?), or the Raspollini 2022 reference is missing.
Line 106 states "we focus here on newer data versions that cover the full mission period of ten years.". If the newer data versions cover 10 years, why do all the tables and figures cover only eight years (2004-2012)? Also, this sentence is missing a final ". "
Lines 152 to 154: It seems that for the MIPAS-ESA processing, different retrieval methods were employed for H2O and HDO. The text needs to explain why this was necessary. Also, why is it "opportune" to use an a priori atmospheric HDO profile that is (3.107 × 10-4) of that of H2O. This is the value in VSMOW, not the atmosphere. In the UTLS the HDO/H2O ratio is closer to (1 × 10-4) so using the 3.107 × 10-4 value might adversely bias the HDO retrievals.
Tables 1 and 2 can be put side-by-side and hence merged into a single table.
Figure 1. Why are the ACE/MIPAS-IMK coincidences ~5 deg. to the South of the ACE/MIPAS-ESA coincidences? So there is no overlap in the ACE data used for MIPAS-IMK validation and for MIPAS-ESA validation -- they are at different latitudes and hence dates. I don't understand why the same ACE data can't be used for both.
Figure 2 should have 1 panel with 3 curves in different colors showing the number of coincidences between: (1) MIPAS-IMK and ACE, (2) MIPAS-ESA and ACE, and (3) MIPAS-IMK and MIPAS-ESA. This will provide the reader more information in less space.
Figure 3: I don't understand the rationale for comparing ACE separately to each MIPAS version. This requires 4 panels and repeats the ACE profiles. Why not have two panels; one for H2O and the other for HDO? Each panel contains the 3 profiles (ACE, MIPAS-IMK, MIPAS-ESA) in different colors. I guess the reason is that ACE data compared with MIPAS-IMK is different from that compared with MIPAS-ESA. In which case you need 4 profiles in each panel: MIPAS-IMK, MIPAS-ESA, ACEIMK, ACEESA.
Figure 6 should be appended to the bottom of fig.5, making a single figure with a single caption. This will allow the reader to compare the features in the dD panels with those in the H2O and HDO panels. This won't be possible with the dD panels on a different page. it will also eliminate repetition in the caption.
Similarly, fig. 8 should be appended to the right of fig.7. It has exactly the same x- and y-axes.
Line 465 states: " the MIPAS instrument shown a negative bias at the troposphere" Change to " the MIPAS instrument shows a negative bias at the troposphere"
Line 420 states:" The general distribution of HDO (Figs 5(c) and 5(d)) shows some similarities to that of H2O (Fig. 5(a) and 5(b)), reflecting that both species have a common in situ source in the stratosphere, i.e., oxidation of CH4 and H2." But HDO comes from CH3D and HD, so change sentence to: " The general distribution of HDO (Fig.s 5(c) and 5(d)) shows some similarities to that of H2O (Fig. 5(a) and 5(b)), reflecting that both species have a common in situ source in the stratosphere, i.e., oxidation of methane and hydrogen."
Line 447 states: "...diagrams over 30S and 30N...". This is ambiguous. Perhaps "...diagrams covering 30S to 30N..."
Line 465:"As it was previously shown in the Fig.3, the MIPAS instrument shown a negative bias at the troposphere" Three grammatical errors in this half sentence. Change to: " As was previously shown in Fig.3, the MIPAS instrument shows a negative bias at the troposphere". Also, I don't see anything negative in Fig.3. Perhaps the authors mean Fig.4?
Line 490 states: " The analysis conducted in this study highlights a higher level of agreement in HDO measurements obtained from ACE-FTS in both comparison cases." This seems to imply that ACE agrees better with MIPAS than MIPAS-IMK and MIPAS-ESA agree with each other?
Line 524 states: "the findings from this study suggest that the MIPAS-IMK dataset provides a more realistic signal for the entire stratosphere". More realistic than what? ACE or MIPAS-ESA.
Line 526 states: "it is crucial to exercise caution when interpreting these results, specifically considering the sampling limitations of ACE-FTS in the tropics, during the period of study, especially at lower altitudes." I don't recall much discussion of this in the main part of the paper. It is true that ACE occultations are sparse in the tropics and that high clouds can often limit penetration of the troposphere. But it seems unfair to ACE to call this an conclusion. And it not clear what altitude range this comment is aimed.
Line 530: "The code in MATLAB is available from the authors upon request." The term "the code" is too vague. Add one sentence explaining what "the code" does.
The format of the References is unfriendly. There is no indentation at the start of a new reference, nor a gap between references. So it is hard to tell where one reference ends and the next begins. Perhaps this is the journal style.
Citation: https://doi.org/10.5194/egusphere-2023-1348-RC1
Karen De Los Ríos et al.
Karen De Los Ríos et al.
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