the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Jul 2025
Version 8 IMK/IAA MIPAS measurements of ClO
Abstract. Global distributions of chlorine monoxide (ClO) were retrieved from infrared limb emission spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), covering the time period from July 2002 to April 2012. The retrieval was performed by constrained non-linear least squares fitting using spectral lines in the fundamental band of ClO around 844 cm-1. The vertical resolution of V8 ClO is 4 km at 18–20 km and 7.5–9.5 km at 40 km altitude. The considerable improvement at 40 km with respect to the previous V5 data version is achieved by extension of the spectral range for retrieval of upper stratospheric ClO. Errors are by far dominated by measurement noise and increase from 0.4–0.5 ppbv at 20 km to 0.8 ppbv at 50 km altitude. Thus, in general, individual ClO profiles are noisy, and profile averaging has to be performed for, e.g., analysis of the upper stratospheric maximum. However, strongly enhanced lower stratospheric ClO amounts of more than 1.5 ppbv during polar winter are well detected in single measurements. Along with the standard representation of the data, an alternative coarse grid representation that obviates the need to apply averaging kernels in certain situations is also provided. Due to improved modeling of the atmospheric continuum and the instrumental offset, the high bias in upper stratospheric ClO that had particularly affected the previous V5 data over the period 2005–2012 has been removed. A comparison with ClO measurements of the Microwave Limb Sounder (MLS) on the Aura satellite shows good agreement between the lower stratospheric enhancements observed by the two instruments in polar winter. There is also good agreement between the upper stratospheric ClO amounts observed in the northern hemisphere and at southern hemispheric low latitudes. With the support of simulations from the Earth system model ECHAM/MESSy Atmospheric Chemistry (EMAC), deviations between the ClO amounts of MIPAS and MLS in the Antarctic lower stratosphere during July and in the upper stratosphere, especially at southern mid- and high latitudes during winter, are attributed to the different local solar times of the measurements.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-3352', Chris Boone, 19 Aug 2025
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AC1: 'Reply on RC1', Norbert Glatthor, 15 Oct 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3352/egusphere-2025-3352-AC1-supplement.pdf
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AC1: 'Reply on RC1', Norbert Glatthor, 15 Oct 2025
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RC2: 'Comment on egusphere-2025-3352', Anonymous Referee #2, 12 Sep 2025
Glatthor et al. is a nice manuscript introducing a new version of the 2002-2012 MIPAS ClO measurements. It is a very welcome contribution to the available data on stratospheric ClO, both in the upper stratosphere and in the lower stratosphere during the polar winter.
Pg. 1, L. 28 - “These days, monitoring of stratospheric ClO from the ground is a routine activity”. Yes, NDACC microwave measurements of ClO are “routine” in the sense that they are available on most days, but this sentence seems to imply that they are generally available at NDACC stations. There are only 2 instruments measuring ClO from the ground, one at Mauna Kea and one at Scott Base.
Pg 3. L. 8 – “For data users who prefer not to work with averaging kernels, we also provide the data on a coarse grid, where averaging kernels do not need to be applied”. Does this mean that there are two different retrievals being performed, or just that a smoothed version of the retrieval is supplied?
Pg 6., L. 13 - “The O3 results from the combined ClO-O3 retrieval are discarded because they are deemed inferior to the standard V8 O3 results.” This should obviously never be the case for optimally chosen parameters for a combined ClO-O3 retrieval, but perhaps a clarification of what is meant by “inferior” would help here. Is it just the case that occasionally the inclusion of noisy channels needed for the ClO retrieval (and not the standard O3 retrieval) cause a bad O3 retrieval? Or does the inclusion of ClO adversely affect almost all O3 retrievals?
Figure 3 – What does the ClO profile used here look like besides being “strongly enhanced”? Also, it would be very helpful here if the ClO spectrum from Figure 1b could be plotted as a third panel with the same horizontal axis as Figures 3a and 3b. Doesn’t the fact that, wherever there is a clear red/blue difference the residual is still very negative imply that there is still not enough ClO in the model?
Pg. 14, L. 17 – “where the related averaging kernels are unity; i.e. the profiles are free of formal a priori information”. This can never be the case. “Near unity” and “contain minimal a priori information” would be okay. It would be good to see these kernels as a fourth panel on Figure 4, which would also show the altitude range where these coarse resolution kernels are near unity.
Pg. 31, L. 13 – The chemistry of the lower stratospheric peak and the upper stratospheric peak is completely different, so it’s not clear from the data here whether the differences are larger because of a larger local time difference or to differences in the sensitivity to local time.
More generally, it would be very helpful somewhere earlier in the manuscript (perhaps on Pg. 26, if not earlier) to discuss the local times of both the MLS and MIPAS measurements, rather than to have the reader wondering about the cause of the bias between MLS and MIPAS shown in Figure 14. Currently it is not until the final figure (Figure 18) of the paper that the sensitivity of daytime measurements to local time is discussed.
Pg. 33, last line – “the MIPAS and MLS data observed during Antarctic winter perfectly fit to the EMAC curve”. Since ClO in this region is dependent on the details of the presence of PSC’s and therefore, when averaged over a large latitude band, on the precise variations in local temperature, the “perfect fit” in Figure 18a for this particular date seems serendipitous. Are the fits on other days during this period similarly good?Citation: https://doi.org/10.5194/egusphere-2025-3352-RC2 -
AC2: 'Reply on RC2', Norbert Glatthor, 15 Oct 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3352/egusphere-2025-3352-AC2-supplement.pdf
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AC2: 'Reply on RC2', Norbert Glatthor, 15 Oct 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-3352', Chris Boone, 19 Aug 2025
-
AC1: 'Reply on RC1', Norbert Glatthor, 15 Oct 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3352/egusphere-2025-3352-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Norbert Glatthor, 15 Oct 2025
-
RC2: 'Comment on egusphere-2025-3352', Anonymous Referee #2, 12 Sep 2025
Glatthor et al. is a nice manuscript introducing a new version of the 2002-2012 MIPAS ClO measurements. It is a very welcome contribution to the available data on stratospheric ClO, both in the upper stratosphere and in the lower stratosphere during the polar winter.
Pg. 1, L. 28 - “These days, monitoring of stratospheric ClO from the ground is a routine activity”. Yes, NDACC microwave measurements of ClO are “routine” in the sense that they are available on most days, but this sentence seems to imply that they are generally available at NDACC stations. There are only 2 instruments measuring ClO from the ground, one at Mauna Kea and one at Scott Base.
Pg 3. L. 8 – “For data users who prefer not to work with averaging kernels, we also provide the data on a coarse grid, where averaging kernels do not need to be applied”. Does this mean that there are two different retrievals being performed, or just that a smoothed version of the retrieval is supplied?
Pg 6., L. 13 - “The O3 results from the combined ClO-O3 retrieval are discarded because they are deemed inferior to the standard V8 O3 results.” This should obviously never be the case for optimally chosen parameters for a combined ClO-O3 retrieval, but perhaps a clarification of what is meant by “inferior” would help here. Is it just the case that occasionally the inclusion of noisy channels needed for the ClO retrieval (and not the standard O3 retrieval) cause a bad O3 retrieval? Or does the inclusion of ClO adversely affect almost all O3 retrievals?
Figure 3 – What does the ClO profile used here look like besides being “strongly enhanced”? Also, it would be very helpful here if the ClO spectrum from Figure 1b could be plotted as a third panel with the same horizontal axis as Figures 3a and 3b. Doesn’t the fact that, wherever there is a clear red/blue difference the residual is still very negative imply that there is still not enough ClO in the model?
Pg. 14, L. 17 – “where the related averaging kernels are unity; i.e. the profiles are free of formal a priori information”. This can never be the case. “Near unity” and “contain minimal a priori information” would be okay. It would be good to see these kernels as a fourth panel on Figure 4, which would also show the altitude range where these coarse resolution kernels are near unity.
Pg. 31, L. 13 – The chemistry of the lower stratospheric peak and the upper stratospheric peak is completely different, so it’s not clear from the data here whether the differences are larger because of a larger local time difference or to differences in the sensitivity to local time.
More generally, it would be very helpful somewhere earlier in the manuscript (perhaps on Pg. 26, if not earlier) to discuss the local times of both the MLS and MIPAS measurements, rather than to have the reader wondering about the cause of the bias between MLS and MIPAS shown in Figure 14. Currently it is not until the final figure (Figure 18) of the paper that the sensitivity of daytime measurements to local time is discussed.
Pg. 33, last line – “the MIPAS and MLS data observed during Antarctic winter perfectly fit to the EMAC curve”. Since ClO in this region is dependent on the details of the presence of PSC’s and therefore, when averaged over a large latitude band, on the precise variations in local temperature, the “perfect fit” in Figure 18a for this particular date seems serendipitous. Are the fits on other days during this period similarly good?Citation: https://doi.org/10.5194/egusphere-2025-3352-RC2 -
AC2: 'Reply on RC2', Norbert Glatthor, 15 Oct 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3352/egusphere-2025-3352-AC2-supplement.pdf
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AC2: 'Reply on RC2', Norbert Glatthor, 15 Oct 2025
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Norbert Glatthor
Thomas von Clarmann
Udo Grabowski
Sylvia Kellmann
Michael Kiefer
Alexandra Laeng
Andrea Linden
Gabriele P. Stiller
Bernd Funke
Maya Garcia-Comas
Manuel Lopez-Puertas
Oliver Kirner
Michelle L. Santee
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Review provided in the attached pdf.