the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Feb 2023
Using OMPS-LP color ratio to extract stratospheric aerosol particle size and concentration with application to volcanic eruptions
Abstract. We develop an algorithm that uses the aerosol extinction at two wavelengths (color ratio) to derive the size and number density for stratospheric aerosols. We apply our algorithm to Ozone Mapping Profiler Suite Limb Profiler (OMPS-LP) L2 and Stratospheric Aerosol and Gas Experiment (SAGE) data. We show that the color ratio between two wavelengths (e.g. 510 nm/869 nm) is insensitive to aerosol concentration and thus can be used to derive aerosol size assuming a log-normal size distribution. With the size and the extinction, we can compute a number density consistent with both wavelengths. Our results compare favorably to balloon borne particle size and concentration measurements. Our results are also consistent with SAGE solar occultation measurements. Finally, we show the background distribution of stratospheric aerosols and the changes in those distributions during the Reikoke and Hunga Tonga-Hunga Ha’apai volcanic eruptions. We also show the evolution of the size and number density of aerosols following both of those eruptions.
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CC1: 'Comment on amt-2023-36', Pasquale Sellitto, 25 Feb 2023
Dear Yi,
thank you for the interesting paper on this simple but effective new methodology. I have a couple of quick questions and comments:
1) It is "Raikoke", not "Reikoke"
2) L25: "dust": do you rather mean "meteoritic dust"?
3) L78-79: "Figure 1a shows...869 nm": what are your assumptions in terms of composition in these Mie calculations (I guess it is sulphates but in case please mention this explicitely"
4) Linked to my previous question, one fundamental question that I have on this method: how do you cope in your method with aerosol mixing, i.e. aerosol layers with particles of different composition? In this case, I imagine that CR is no more insensitive to size. This is quite critical for first stages of some volcanic eruptions, like Raikoke (there was a significant fraction of ash in the early sulphate plume).
5) For Hunga Tonga, there are size distribution measurements shown in Kloss et al. 2022 (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099394), that are ideally perfect correlative data for your method.
6) For the rapid formation of sulphate aerosol in Hunga Tonga plume (which is linked to their size evolution), you cite model studies of Zhu et al 2022 (L234) but this is also show with observations in Sellitto et al. 2022 (https://www.nature.com/articles/s43247-022-00618-z), as well as hypothese of why observed SO2 emissions where small (L228) and estimations of the radiative impacts of Hunga Tonga plume (L227), and should then be cited in your discussion.
My best regards,
Pasquale Sellitto
Citation: https://doi.org/10.5194/amt-2023-36-CC1 - AC4: 'Reply on CC1', Yi Wang, 15 Jun 2023
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CC2: 'Comment on amt-2023-36', Travis N. Knepp, 06 Mar 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-CC2-supplement.pdf
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AC1: 'Reply on CC2', Yi Wang, 04 Apr 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-AC1-supplement.pdf
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CC4: 'Reply on AC1', Travis N. Knepp, 19 Apr 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-CC4-supplement.pdf
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CC4: 'Reply on AC1', Travis N. Knepp, 19 Apr 2023
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AC1: 'Reply on CC2', Yi Wang, 04 Apr 2023
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CC3: 'Comment on amt-2023-36', Peter F. Bernath, 18 Mar 2023
This is an interesting paper, but some improvements should be implemented.
- The interpretation of the color ratio depends entirely on Mie scattering calculations carried out with SASKTRAN. These calculations depend on input parameters and assumptions, which need to be explicitly stated. In particular, the results depend on the assumed composition (weight % of sulfuric acid) and the optical constants used. What is the temperature of the optical constants and was there any effort to match the optical constant temperature to the atmospheric temperature? The assumption of 1.6 for the width of the log-normal distribution is noted, but the systematic error on the median radius from this assumption is not estimated. Some discussion of systematic errors introduced by these various assumptions should be included.
- Two recent papers on the properties of stratospheric sulfate aerosols from Raikoke, Tonga and Nabro volcanic eruptions based on ACE-FTS spectra have been overlooked [1,2]. These papers can help with point 1 above and with particle size comparisons with independent measurements.
- The plume from the Raikoke volcanic eruption traveled both northwards and southwards, not just South [2,3]. “The eruption cloud is initially at 50° N and moves southward so the aerosols are detected at more southerly latitudes at a later time.”
References
- Bernath, C. Boone, A. Pastorek, D. Cameron and M. Lecours, Satellite characterization of global stratospheric sulfate aerosols released by Tonga volcano, J. Quant. Spectrosc. Rad. Transfer 299, 108520 (2023). Doi: 10.1016/j.jqsrt.2023.108520
- D. Boone, P. F. Bernath, K. LaBelle and J. Crouse, Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption, J. Geophys. Res.: Atmospheres 127, e2022JD036600 (2022). Doi: 10.1029/2022JD036600
- D. Cameron, P. Bernath and C. Boone, Sulfur Dioxide from the Atmospheric Chemistry Experiment (ACE) Satellite, J. Quant. Spectrosc. Rad. Transfer 258, 107341 (2020). DOI: 10.1016/j.jqsrt.2020.107341
Citation: https://doi.org/10.5194/amt-2023-36-CC3 - AC5: 'Reply on CC3', Yi Wang, 15 Jun 2023
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RC1: 'Comment on amt-2023-36', Anonymous Referee #1, 12 Apr 2023
- AC2: 'Reply on RC1', Yi Wang, 15 Jun 2023
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RC2: 'Comment on amt-2023-36', Anonymous Referee #2, 22 Apr 2023
Review of "Using OMPS-LP color ratio to extract stratospheric aerosol particle size
and concentration with application to volcanic eruptions", manuscript prepared for
AMT by Wang and co-authors.This manuscript describes an adapted application of an existing method to derive aerosol
particle size distribution parameters from measurements of aerosol extinction from
the OMPS-LP limb-profiling sensor (e.g. Taha et al., 2021).The method is applied to analyse vertical and meridional variations in microphysical
aerosol properties in background stratosphere conditions and from two volcanic
case studies, the 2019 Raikoke and 2022 Hunga-Tonga large-magnitude explosive eruptions,For the Raikoke case, the derived number concentrations are evaluated comparing to
in-situ optical particle counter measurements from high-altitude balloon soundings
from North America. The OMPS-derived particle size and number concentrations are compared
also to similar colour-ratio analysis from the SAGE-III sensor.
The Figures 9 and 10 represent an important and valuable first analysis of the size variations
evident across the vertical profile of the Hunga-Tonga stratospheric aerosol enhancement.The paper is certainly appropriate for AMT, and the analysis of the Hunga-Tonga will be of
particular interest with the unexpectedly strong aerosol optical depth. The microphysical
parameters are relevant the two hypotheses for the effect -- that the aerosol
scattering is amplified by the co-emitted water vapour, and whether there was additional
primary emitted aerosol (from the vaporised seawater and/or in-plume-oxidised sulphate).I have seen that three other revieweers have submitted reviews on the manuscript already,
and although I have not referred to their comments when carrying out this review, my comments
here are focused on improving the Introduction and Methods section, and in relation to the
current interpretation of Figure 3.Given that this is a manuscript submitted to the specialist journal Atmospheric Measurement
Techniques, the methods section requires substantial improvement, and whilst I understand
most interest will of course be towards the main scientific results re: the particle size
variations, the section 2 requires better summary explanation of the methods.In some places the scientific writing style needs to be improved for an article in a
peer-reviewed journal, avoiding "our algorithm" etc., written in a more formal/impersonal tense.
A particular substantial revision, is re: equation 1 of the paper, which as currently written
does not convey the approximate nature of the relationship assumed when inferring the
large-scale variations in particle number and size.That said, the article is certainly publishable in Atmospheric Measurement Techiques
once the text has been sufficiently improved. The variations shown for the Hunga-Tonga
and Raikoke aerosol clouds will be of substantial interest to the stratospheric aerosol
community.Please see below a list of specific revisions to improve the text, and please also
check for where there may still be other parts of the text where the wording could
be improved.General Comments
----------------GC1) Finding re: number density independence (text interpreting Figure 1, lines 88-89)
The first of the stated findings in the Abstract (3rd sentence), reached from interpreting
Figures 1a and 1b, is not sufficiently demonstrated. The text on lines 88-89 states
"This figure shows that the particle size is only a function of CR, and is independent of
the number density." There are 2 stated findings in the sentence about particle size,
and both are questionable, unless clarified to a specific context.The upper Figure (1a) shows the curve in colour ratio with particle size from Mie calculations,
essentially presenting how much larger the aerosol extinction is at the shorter of the
two wavelengths, compared to the longer wavelength, comparing 510nm & 745nm aerosol extinction
to that at the reference wavelength of 869nm.The lower Figure (1b) shows how a set of assumed number concentrations translate into
aerosol extinctions at 510nm and 869nm wavelengths, for a range of assumed median sizes.The reasoning for why the Figure shows this shows one can conclude the number concentration
is independent of the number density is far from clear.The methodology in the paper assumes this to be the case, within a particular range of
particle sizes (e.g. particle sizes sufficiently scattering at the corresponding wavelength
[e.g. above some threshold value in extinction-cross-section at that wavelength]).But the text is not correct to state that can be inferred from what is shown in the Figure.
I suggest to delete that text on lines 88-89, and re-write the 3rd sentence of the Abstract
that states this to be a finding of the study (lines 10-11).GC2) Statements re: methods too general or unclarified
The sentence from GC1) is an example of several statements within the manuscript (including
within the Abstract) where results are stated too generally, with insufficient communication
of the specifics.Given that this manuscript is within a specialist journal such as Atmospheric Measurement
Techniques, the scientific writing on the methods needs to be quite precise.Whilst I understand that the text describing equation 1 is aiming to present the basis of the
Bourassa et al. (2007,2008) method, the explanation on lines 75-83 need to be improved.For example the sentence on line 76 states "In computing the color ratio of aerosol extinction,
the number density cancels out". Whilst that could be OK within a paragraph describing a
methdological description, here this appears more prominently, and out of that context.
My suggestion here is simply to delete this, expression, since it is part of the methodology
already described comprehensively in Bourassa et al. (2007,2008).See specific revisions SR9 and SR10
GC3) Comparisons to balloon-borne laser particle counter measurements (Section 3.1)
This is the other part of the text where the method needs to be better explained
(given this is submitted for an Atmospheric Measurement Techniques paper)The text on lines 125-126 need to provide the location of the sounding compared to,
and the specific size-cut for the particle number shown in the black line in Figure 3b.
(this information to be re-stated also in the Figure caption).The terminology can be confusing because the Wyoming laser-OPC (WL-OPC) was developed
at Boulder (see Ward et al. 2014) and the new lightweight OPC system is called L-OPC
(see Kalnajs and Deshler, 2022).The cavity-laser OPC is described in Ward et al. (2014), with multiple size channels,
down to 75nm radius (75, 150, 250, 500nm, and 1.0, 2.5, 5.0, and 15.0 microns).For these comparisons to the OMPS-LP aerosol extinction, I am assuming the 75nm radius
channel is shown, but this is important considering also that the original OPC40 and
OPC25 only measured to 150nm particle radius (see Deshler et al., 2019).Please add, within the text on lines 125-126, and the caption to Figure 3,
the minimum particle size for the size-resolved number concentration shown.Given the Mie scattering curves will of course vary for the different wavelengths
considered, the minimum size is an important issue here.Related to this a suggestion is to add a dashed line for the R>150nm number concentration
(and possibly also the 250nm line, in dot-dashed or so).The overestimation shown in the 16-18km altitude-range could potentially be due to
only some proportion of those R>75nm particles being measured, even at the shorter
of the two OMPS-LP wavelengths. I appreciate this is a retrieval, but then the issue of
what particle sizes are represented within the two aerosol extinction metrics within
the color-ratio particle size method probably justifies considering an uncertainty-range
across more than 1 of the size channels (particle size cuts) in the comparisons.List of specific revisions
--------------------------SR1) Abstract, lines 8-9 -- This initial text "We have developed an algorithm" might make some
readers assume the MS is to explain some development of a new algorithm, but the MS is rather
applying an existing method already developed for the OSIRIS data (Bourassa et al., 2007, 2008),
to OMPS measurements, comparing to in-situ measurements for two recent volcanic case studies.
For this initial sentence better to put the object of the sentence (derive the size...)
at the start of the sentence, with also referring more generally to "aerosol microphysical
parameters" rather than the specifics in this initial sentence.Please change "We develop an algorithm that uses the aerosol extinction at two wavelengths..."
instead to "We apply an existing method to derive aerosol microphysical parameters from
OMPS dual-wavelength aerosol exinction measurements, to analyse particle size variations
for two recent stratospheric volcanic case studies." or similar.SR2) Abstract, lines 9-10
With the above re-wording, the first part of the 2nd sentence of the Abstract is already
integrated into the above re-worded 1st sentence, and the latter part re: SAGE should be
stated later, being clear this is SAGE-III on ISS.SR3) Abstract, line 10 -- This 3rd sentence of the Abstract also needs to be re-worded, with the
current text "We show that the color ratio between two wavelengths is insensitive to number density."
suggesting the manuscript is presenting this as a finding from the study.Figure 1 is very useful in showing the variation with particle size and relative magnitudes of
monochromatic aerosol extinction at 3 specified wavelengths, for a log-normally distributed
liquid aqueous sulphuric acid solution aerosol population
(for an assumed refractive index spectrum and water content/weight-percent).However, as is explained in General Comment 1 above, the text on lines 88-89 is not correct in stating
the Figure shows the color ratio is independent of number density. I understand this is an assumption
within the methods explained in the Bourassa et al. (2007, 2008) studies, and for a particular range
of particle sizes, it's a reasonable assumption to make.
However the Abstract should not present as a finding from the study.Also, the "and thus" in the 2nd part of the sentence (with the current wording) does not follow,
and suggests a misunderstanding re: what is assumed in the method,
with the wording "We show the color ratio between two wavelengths (e.g. 510nm/869nm)
is insensitive to aerosol concentration, and thus can be used to derive aerosol size
assuming a log-normal size distribution."Within the re-constructed sentence, the color ratio metric also needs to better communicated,
a suggested re-wording to have "of aerosol extinctions at" in place of "between", and
change "(e.g. 510nm/869nm)" instead to "(510mm and 869nm)".My specific suggestion for the 2nd part of this sentence is to delete "and thus can be used to",
and also change "We show that" instead to a re-worded sentence similar to below:"The color ratio between aerosol extinction at two wavelengths is used to derive from satellite
measurements large-scale particle size variations within volcanic aerosol clouds in the stratosphere."SR4) Abstract, lines 12 -- Re-word "With the size and extinction, we can compute a number density
consistent with both wavelengths". The particle size is being inferred from the two-wavelength
aerosol extinctions, not measured directly.
With the re-constructed preceding sentences (from SR3), suggest to instead have this sentence be
to explain some greater specifics in the method, prior to its application for profiling the
size distribution of the Raikoke and Hunga Tonga aerosol clouds.A suggested re-wording "With the size and extinction, we can compute..."
instead with "As a further microphysical Consistent with the two extinctionSR5) Abstract, lines 13-14 -- Please re-word this sentence to be more specific re: the comparisons
between the particle size variations from OMPS-LP and those derived from SAGE-III on ISS,
giving some specifics about how well the two size products compare.SR6) Introduction, lines 21-22 -- change "have been connected to short-term changes in climate"
instead to "major eruptions causing substantial short-term changes in climate", or similar.The first sentence (of this 1st paragraph of the introduction) mentions the volcanic impacts
on climate, but this adaptation of the sentence is then consistent with the strong (but
temporary) radiative forcings after historical very large-magnitude explosive tropical eruptions.SR7) Introduction, line 25 -- Please re-word this sentence to be clearer what is meant by "dust"
in this context ("Volcanic ash, Pyro-CB smoke and dust") -- presumably it is cosmic dust (i.e.
meteoric aerosol) that is meant here, right? Suggest to have the re-worded text provide this
information in relation to citing a recent observational studies for each of these non-sulphate
stratospheric aerosol constituents. Suggestions are Vernier et al. (2016), for volcanic ash,
Khaykin et al. (2020) for pyro-Cb smoke, and Schneider et al. (2021) for meteoric aerosol.With this re-wording the text on line 26, suggest to cite paper also for the volcanic ash heating
(Muser et al., 2020), and cite the Yu et al. (2019) for the wildfire smoke heating effect.
The cosmic dust (meteoric smoke) may be present at sizes smaller than for wildfire smoke
and volcanic ash, also some components dissolving into the sulphuric acid solution aerosol particles
(see James et al., 2023), the heating effect is primarily associated with the smoke and ash.SR8) Introduction, lines 32-34
Re-word "has provided global monitoring of the stratospheric aerosol layer since 1975" because
the SAGE and SAM-II record only began in 1979 (see McCormick et al., 1977). The original testing
of the SAM sensor on the Apollo Soyuz mission was in 1975, but the global monitoring only
began in 1979.Re: the text on the solar occultation methods, the so-called "onion-peeling" retrieval method
was originally developed in the 1960s (Edward Ney group at the University of Minnesota), and
it will help retain the heritage of the instrument development to cite the Pepin (1969)
report that first documented the technique, and the Rosen et al. (1969) which shows (Figure 4)
the only peer-reviewed paper showing the initial application of the methods to balloon-borne
solar extinction measurements, and later further developed for application to the first satellite
measurements of the stratospheric aerosol layer (the SAM, SAM-II, McCormick et al., 1979),
and then SAGE, SAGE-II and SAGE-III series of satellite measurements.SR9) Section 2, line 76-78
Add ", at wavelength $\lamda$, " after "The aerosol extinction" and add subscript
lamda symbol to the two wavelength-dependent symbols in equation 1 (sigma and AR).In addition, please change the abbreviation "AE" for aerosol extinction, as this may
initially confuse some readers, given the related size-associated aerosol metric
"Angstrom exponent". Please change all occurrences of "AE" instead to either "k"
(used in the Bourassa et al. (2007, 2008) papers) or other terminology
(the letter b is used, subscript "ext" to denote aerosol extinction in
Seinfeld & Pandis (2006).It also needs to be stated explicitly that these calculations are based on an assumed log-normal
size distirbution, with also the associated water content (sulphuric acid and water composition).As explained in General Comment GC2, please delete the two short sentences lines 77-78 as this
statement does not follow from what is shown. The information and associated assumptions are
explained within context in the Bourassa et al. (2007,2008) papers.SR10) Section 2, lines 82-83
As mentioned in General Comment GC2, the text "...but as the two wavelengths approach each other"
is too colloquial and needs to be formalised. Also, the "Any two distinct wavelengths can
be chosen" at the start of the sentence also does not need to be stated. Suggested re-structuring
to better explain the issue.Suggest to re-word the original text:
"Any two distinct wavelengths can be chosen for CR, but as the two wavelengths approach each other
Fig. 1a shows that the CR gradient decreases and thus the uncertainty in the retrieved
size increases."instead to
"For OMPS-LP wavelengths closer to the reference 869nm wavelength, the gradient in the colour
ratio curve is less steep, causing an increased uncertainty in the retrieved particle size."It is worth noting also that the 869nm aerosol extinction measurement is "cleanest" retrieval
in relation to effects from other species, and this must also be considered in relation to
how the errors/uncertainty differ between different color-ratio wavelength-pairs.SR11) Figure 1 caption, lines 431-435.
Although it is not stated explicitly, my understanding is that these calculations are based
on a log-normally distributed aerosol, with geometric standard deviation of 1.6, following
the specification within SASKTRAN. This should be stated in the caption to Figure 1.SR12) Section 2, line 368 -- formatting error re: Loughman et al. (2015) reference.
References
----------Bourassa et al. (2007) Stratospheric aerosol retrieval with OSIRIS limb scatter measurements,
J. Geophys. Res., 112, D10 217, https://doi.org/10.1029/2006JD008079.Bourassa et al. (2008) Retrieval of stratospheric aerosol size information from OSIRIS
limb scattered sunlight spectra, Atmos. Chem. Phys., 8, 6375–6380,
https://doi.org/10.5194/acp-8-6735-2008.James et al. (2023) The importance of acid-processed meteoric smoke relative to meteoric
fragments for crystal nucleation in polar stratospheric clouds
Atmos. Chem. Phys., 23, 2215–2233, https://doi.org/10.5194/acp-23-2215-2023Khaykin et al. (2021) "The 2019/20 Australian wildfires generated
a persistent smoke-charged vortex rising up to 35 km altitude"
Comms. Earth Env., https://doi.org/10.1038/s43247-020-00022-5McCormick et al. (1978) Satellite studies of the stratospheric aerosol
Bulletin of Amer. Meteorol. Soc., vol. 60, no. 9, 1038-1046.
https://doi.org/10.1175/1520-0477(1979)060<1038:SSOTSA>2.0.CO;2Muser et al. (2020) Particle aging and aerosol–radiation interaction affect
volcanic plume dispersion: evidence from the Raikoke 2019 eruption,
Atmos. Chem. Phys., 20, 15015–15036, https://doi.org/10.5194/acp-20-15015-2020Pepin T. J. (1969) "The Use of Extinction from High Altitude Balloons as a Probe
of the Atmospheric Aerosols", Univ. Minn. progress report, Oct, 1969
https://apps.dtic.mil/sti/pdfs/AD0696527.pdfPepin, T. J. (1977) "Inversion of solar extinction data from the Apollo-Soyez test project
Stratospheric aerosol measurement (ASTP/SAM) experiment", volume 1, 529-544, NASA report SP-442.
https://ntrs.nasa.gov/citations/19780009145Rosen, J. M. (1969) "Stratospheric dust and its relationship to the meteoric influx",
Space Science Reviews, vol. 9, 58-89, https://doi.org/10.1007/BF00187579 (see Figure 4).Schneider et al. (2021) " Aircraft-based observation of meteoric material in
lower-stratospheric aerosol particles between 15N and 68N", Atmos. Chem. Phys.,
vol. 21 989-1013, https://doi.org/10.5194/acp-21-989-2021Seinfeld and Pandis (2006)
Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 2nd Edition, Wiley publisher.
John H. Seinfeld, Spyros N. PandisVernier et al. (2016) "In situ and space-based observations of the Kelud volcanic plume:
The persistence of ash in the lower stratosphere", J. Geophys. Res., vol. 121,
11,104–11,118, http://doi.org/10.1002/2016JD025344.Citation: https://doi.org/10.5194/amt-2023-36-RC2 -
RC3: 'Reply on RC2', Anonymous Referee #2, 22 Apr 2023
There seems to be glitch with the electronic journal re-formatting this review, with
strange double-spacing added when it appeared in the mobile-accessible format.
I had this previously with a review I submitted, with it appearing fine when I reviewed it
to approve it at the "Submit" option.
I am attaching a file here with PDF of the review, and this should then be easier to read.- AC3: 'Reply on RC2', Yi Wang, 15 Jun 2023
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RC3: 'Reply on RC2', Anonymous Referee #2, 22 Apr 2023
Status: closed
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CC1: 'Comment on amt-2023-36', Pasquale Sellitto, 25 Feb 2023
Dear Yi,
thank you for the interesting paper on this simple but effective new methodology. I have a couple of quick questions and comments:
1) It is "Raikoke", not "Reikoke"
2) L25: "dust": do you rather mean "meteoritic dust"?
3) L78-79: "Figure 1a shows...869 nm": what are your assumptions in terms of composition in these Mie calculations (I guess it is sulphates but in case please mention this explicitely"
4) Linked to my previous question, one fundamental question that I have on this method: how do you cope in your method with aerosol mixing, i.e. aerosol layers with particles of different composition? In this case, I imagine that CR is no more insensitive to size. This is quite critical for first stages of some volcanic eruptions, like Raikoke (there was a significant fraction of ash in the early sulphate plume).
5) For Hunga Tonga, there are size distribution measurements shown in Kloss et al. 2022 (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099394), that are ideally perfect correlative data for your method.
6) For the rapid formation of sulphate aerosol in Hunga Tonga plume (which is linked to their size evolution), you cite model studies of Zhu et al 2022 (L234) but this is also show with observations in Sellitto et al. 2022 (https://www.nature.com/articles/s43247-022-00618-z), as well as hypothese of why observed SO2 emissions where small (L228) and estimations of the radiative impacts of Hunga Tonga plume (L227), and should then be cited in your discussion.
My best regards,
Pasquale Sellitto
Citation: https://doi.org/10.5194/amt-2023-36-CC1 - AC4: 'Reply on CC1', Yi Wang, 15 Jun 2023
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CC2: 'Comment on amt-2023-36', Travis N. Knepp, 06 Mar 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-CC2-supplement.pdf
-
AC1: 'Reply on CC2', Yi Wang, 04 Apr 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-AC1-supplement.pdf
-
CC4: 'Reply on AC1', Travis N. Knepp, 19 Apr 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-CC4-supplement.pdf
-
CC4: 'Reply on AC1', Travis N. Knepp, 19 Apr 2023
-
AC1: 'Reply on CC2', Yi Wang, 04 Apr 2023
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CC3: 'Comment on amt-2023-36', Peter F. Bernath, 18 Mar 2023
This is an interesting paper, but some improvements should be implemented.
- The interpretation of the color ratio depends entirely on Mie scattering calculations carried out with SASKTRAN. These calculations depend on input parameters and assumptions, which need to be explicitly stated. In particular, the results depend on the assumed composition (weight % of sulfuric acid) and the optical constants used. What is the temperature of the optical constants and was there any effort to match the optical constant temperature to the atmospheric temperature? The assumption of 1.6 for the width of the log-normal distribution is noted, but the systematic error on the median radius from this assumption is not estimated. Some discussion of systematic errors introduced by these various assumptions should be included.
- Two recent papers on the properties of stratospheric sulfate aerosols from Raikoke, Tonga and Nabro volcanic eruptions based on ACE-FTS spectra have been overlooked [1,2]. These papers can help with point 1 above and with particle size comparisons with independent measurements.
- The plume from the Raikoke volcanic eruption traveled both northwards and southwards, not just South [2,3]. “The eruption cloud is initially at 50° N and moves southward so the aerosols are detected at more southerly latitudes at a later time.”
References
- Bernath, C. Boone, A. Pastorek, D. Cameron and M. Lecours, Satellite characterization of global stratospheric sulfate aerosols released by Tonga volcano, J. Quant. Spectrosc. Rad. Transfer 299, 108520 (2023). Doi: 10.1016/j.jqsrt.2023.108520
- D. Boone, P. F. Bernath, K. LaBelle and J. Crouse, Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption, J. Geophys. Res.: Atmospheres 127, e2022JD036600 (2022). Doi: 10.1029/2022JD036600
- D. Cameron, P. Bernath and C. Boone, Sulfur Dioxide from the Atmospheric Chemistry Experiment (ACE) Satellite, J. Quant. Spectrosc. Rad. Transfer 258, 107341 (2020). DOI: 10.1016/j.jqsrt.2020.107341
Citation: https://doi.org/10.5194/amt-2023-36-CC3 - AC5: 'Reply on CC3', Yi Wang, 15 Jun 2023
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RC1: 'Comment on amt-2023-36', Anonymous Referee #1, 12 Apr 2023
- AC2: 'Reply on RC1', Yi Wang, 15 Jun 2023
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RC2: 'Comment on amt-2023-36', Anonymous Referee #2, 22 Apr 2023
Review of "Using OMPS-LP color ratio to extract stratospheric aerosol particle size
and concentration with application to volcanic eruptions", manuscript prepared for
AMT by Wang and co-authors.This manuscript describes an adapted application of an existing method to derive aerosol
particle size distribution parameters from measurements of aerosol extinction from
the OMPS-LP limb-profiling sensor (e.g. Taha et al., 2021).The method is applied to analyse vertical and meridional variations in microphysical
aerosol properties in background stratosphere conditions and from two volcanic
case studies, the 2019 Raikoke and 2022 Hunga-Tonga large-magnitude explosive eruptions,For the Raikoke case, the derived number concentrations are evaluated comparing to
in-situ optical particle counter measurements from high-altitude balloon soundings
from North America. The OMPS-derived particle size and number concentrations are compared
also to similar colour-ratio analysis from the SAGE-III sensor.
The Figures 9 and 10 represent an important and valuable first analysis of the size variations
evident across the vertical profile of the Hunga-Tonga stratospheric aerosol enhancement.The paper is certainly appropriate for AMT, and the analysis of the Hunga-Tonga will be of
particular interest with the unexpectedly strong aerosol optical depth. The microphysical
parameters are relevant the two hypotheses for the effect -- that the aerosol
scattering is amplified by the co-emitted water vapour, and whether there was additional
primary emitted aerosol (from the vaporised seawater and/or in-plume-oxidised sulphate).I have seen that three other revieweers have submitted reviews on the manuscript already,
and although I have not referred to their comments when carrying out this review, my comments
here are focused on improving the Introduction and Methods section, and in relation to the
current interpretation of Figure 3.Given that this is a manuscript submitted to the specialist journal Atmospheric Measurement
Techniques, the methods section requires substantial improvement, and whilst I understand
most interest will of course be towards the main scientific results re: the particle size
variations, the section 2 requires better summary explanation of the methods.In some places the scientific writing style needs to be improved for an article in a
peer-reviewed journal, avoiding "our algorithm" etc., written in a more formal/impersonal tense.
A particular substantial revision, is re: equation 1 of the paper, which as currently written
does not convey the approximate nature of the relationship assumed when inferring the
large-scale variations in particle number and size.That said, the article is certainly publishable in Atmospheric Measurement Techiques
once the text has been sufficiently improved. The variations shown for the Hunga-Tonga
and Raikoke aerosol clouds will be of substantial interest to the stratospheric aerosol
community.Please see below a list of specific revisions to improve the text, and please also
check for where there may still be other parts of the text where the wording could
be improved.General Comments
----------------GC1) Finding re: number density independence (text interpreting Figure 1, lines 88-89)
The first of the stated findings in the Abstract (3rd sentence), reached from interpreting
Figures 1a and 1b, is not sufficiently demonstrated. The text on lines 88-89 states
"This figure shows that the particle size is only a function of CR, and is independent of
the number density." There are 2 stated findings in the sentence about particle size,
and both are questionable, unless clarified to a specific context.The upper Figure (1a) shows the curve in colour ratio with particle size from Mie calculations,
essentially presenting how much larger the aerosol extinction is at the shorter of the
two wavelengths, compared to the longer wavelength, comparing 510nm & 745nm aerosol extinction
to that at the reference wavelength of 869nm.The lower Figure (1b) shows how a set of assumed number concentrations translate into
aerosol extinctions at 510nm and 869nm wavelengths, for a range of assumed median sizes.The reasoning for why the Figure shows this shows one can conclude the number concentration
is independent of the number density is far from clear.The methodology in the paper assumes this to be the case, within a particular range of
particle sizes (e.g. particle sizes sufficiently scattering at the corresponding wavelength
[e.g. above some threshold value in extinction-cross-section at that wavelength]).But the text is not correct to state that can be inferred from what is shown in the Figure.
I suggest to delete that text on lines 88-89, and re-write the 3rd sentence of the Abstract
that states this to be a finding of the study (lines 10-11).GC2) Statements re: methods too general or unclarified
The sentence from GC1) is an example of several statements within the manuscript (including
within the Abstract) where results are stated too generally, with insufficient communication
of the specifics.Given that this manuscript is within a specialist journal such as Atmospheric Measurement
Techniques, the scientific writing on the methods needs to be quite precise.Whilst I understand that the text describing equation 1 is aiming to present the basis of the
Bourassa et al. (2007,2008) method, the explanation on lines 75-83 need to be improved.For example the sentence on line 76 states "In computing the color ratio of aerosol extinction,
the number density cancels out". Whilst that could be OK within a paragraph describing a
methdological description, here this appears more prominently, and out of that context.
My suggestion here is simply to delete this, expression, since it is part of the methodology
already described comprehensively in Bourassa et al. (2007,2008).See specific revisions SR9 and SR10
GC3) Comparisons to balloon-borne laser particle counter measurements (Section 3.1)
This is the other part of the text where the method needs to be better explained
(given this is submitted for an Atmospheric Measurement Techniques paper)The text on lines 125-126 need to provide the location of the sounding compared to,
and the specific size-cut for the particle number shown in the black line in Figure 3b.
(this information to be re-stated also in the Figure caption).The terminology can be confusing because the Wyoming laser-OPC (WL-OPC) was developed
at Boulder (see Ward et al. 2014) and the new lightweight OPC system is called L-OPC
(see Kalnajs and Deshler, 2022).The cavity-laser OPC is described in Ward et al. (2014), with multiple size channels,
down to 75nm radius (75, 150, 250, 500nm, and 1.0, 2.5, 5.0, and 15.0 microns).For these comparisons to the OMPS-LP aerosol extinction, I am assuming the 75nm radius
channel is shown, but this is important considering also that the original OPC40 and
OPC25 only measured to 150nm particle radius (see Deshler et al., 2019).Please add, within the text on lines 125-126, and the caption to Figure 3,
the minimum particle size for the size-resolved number concentration shown.Given the Mie scattering curves will of course vary for the different wavelengths
considered, the minimum size is an important issue here.Related to this a suggestion is to add a dashed line for the R>150nm number concentration
(and possibly also the 250nm line, in dot-dashed or so).The overestimation shown in the 16-18km altitude-range could potentially be due to
only some proportion of those R>75nm particles being measured, even at the shorter
of the two OMPS-LP wavelengths. I appreciate this is a retrieval, but then the issue of
what particle sizes are represented within the two aerosol extinction metrics within
the color-ratio particle size method probably justifies considering an uncertainty-range
across more than 1 of the size channels (particle size cuts) in the comparisons.List of specific revisions
--------------------------SR1) Abstract, lines 8-9 -- This initial text "We have developed an algorithm" might make some
readers assume the MS is to explain some development of a new algorithm, but the MS is rather
applying an existing method already developed for the OSIRIS data (Bourassa et al., 2007, 2008),
to OMPS measurements, comparing to in-situ measurements for two recent volcanic case studies.
For this initial sentence better to put the object of the sentence (derive the size...)
at the start of the sentence, with also referring more generally to "aerosol microphysical
parameters" rather than the specifics in this initial sentence.Please change "We develop an algorithm that uses the aerosol extinction at two wavelengths..."
instead to "We apply an existing method to derive aerosol microphysical parameters from
OMPS dual-wavelength aerosol exinction measurements, to analyse particle size variations
for two recent stratospheric volcanic case studies." or similar.SR2) Abstract, lines 9-10
With the above re-wording, the first part of the 2nd sentence of the Abstract is already
integrated into the above re-worded 1st sentence, and the latter part re: SAGE should be
stated later, being clear this is SAGE-III on ISS.SR3) Abstract, line 10 -- This 3rd sentence of the Abstract also needs to be re-worded, with the
current text "We show that the color ratio between two wavelengths is insensitive to number density."
suggesting the manuscript is presenting this as a finding from the study.Figure 1 is very useful in showing the variation with particle size and relative magnitudes of
monochromatic aerosol extinction at 3 specified wavelengths, for a log-normally distributed
liquid aqueous sulphuric acid solution aerosol population
(for an assumed refractive index spectrum and water content/weight-percent).However, as is explained in General Comment 1 above, the text on lines 88-89 is not correct in stating
the Figure shows the color ratio is independent of number density. I understand this is an assumption
within the methods explained in the Bourassa et al. (2007, 2008) studies, and for a particular range
of particle sizes, it's a reasonable assumption to make.
However the Abstract should not present as a finding from the study.Also, the "and thus" in the 2nd part of the sentence (with the current wording) does not follow,
and suggests a misunderstanding re: what is assumed in the method,
with the wording "We show the color ratio between two wavelengths (e.g. 510nm/869nm)
is insensitive to aerosol concentration, and thus can be used to derive aerosol size
assuming a log-normal size distribution."Within the re-constructed sentence, the color ratio metric also needs to better communicated,
a suggested re-wording to have "of aerosol extinctions at" in place of "between", and
change "(e.g. 510nm/869nm)" instead to "(510mm and 869nm)".My specific suggestion for the 2nd part of this sentence is to delete "and thus can be used to",
and also change "We show that" instead to a re-worded sentence similar to below:"The color ratio between aerosol extinction at two wavelengths is used to derive from satellite
measurements large-scale particle size variations within volcanic aerosol clouds in the stratosphere."SR4) Abstract, lines 12 -- Re-word "With the size and extinction, we can compute a number density
consistent with both wavelengths". The particle size is being inferred from the two-wavelength
aerosol extinctions, not measured directly.
With the re-constructed preceding sentences (from SR3), suggest to instead have this sentence be
to explain some greater specifics in the method, prior to its application for profiling the
size distribution of the Raikoke and Hunga Tonga aerosol clouds.A suggested re-wording "With the size and extinction, we can compute..."
instead with "As a further microphysical Consistent with the two extinctionSR5) Abstract, lines 13-14 -- Please re-word this sentence to be more specific re: the comparisons
between the particle size variations from OMPS-LP and those derived from SAGE-III on ISS,
giving some specifics about how well the two size products compare.SR6) Introduction, lines 21-22 -- change "have been connected to short-term changes in climate"
instead to "major eruptions causing substantial short-term changes in climate", or similar.The first sentence (of this 1st paragraph of the introduction) mentions the volcanic impacts
on climate, but this adaptation of the sentence is then consistent with the strong (but
temporary) radiative forcings after historical very large-magnitude explosive tropical eruptions.SR7) Introduction, line 25 -- Please re-word this sentence to be clearer what is meant by "dust"
in this context ("Volcanic ash, Pyro-CB smoke and dust") -- presumably it is cosmic dust (i.e.
meteoric aerosol) that is meant here, right? Suggest to have the re-worded text provide this
information in relation to citing a recent observational studies for each of these non-sulphate
stratospheric aerosol constituents. Suggestions are Vernier et al. (2016), for volcanic ash,
Khaykin et al. (2020) for pyro-Cb smoke, and Schneider et al. (2021) for meteoric aerosol.With this re-wording the text on line 26, suggest to cite paper also for the volcanic ash heating
(Muser et al., 2020), and cite the Yu et al. (2019) for the wildfire smoke heating effect.
The cosmic dust (meteoric smoke) may be present at sizes smaller than for wildfire smoke
and volcanic ash, also some components dissolving into the sulphuric acid solution aerosol particles
(see James et al., 2023), the heating effect is primarily associated with the smoke and ash.SR8) Introduction, lines 32-34
Re-word "has provided global monitoring of the stratospheric aerosol layer since 1975" because
the SAGE and SAM-II record only began in 1979 (see McCormick et al., 1977). The original testing
of the SAM sensor on the Apollo Soyuz mission was in 1975, but the global monitoring only
began in 1979.Re: the text on the solar occultation methods, the so-called "onion-peeling" retrieval method
was originally developed in the 1960s (Edward Ney group at the University of Minnesota), and
it will help retain the heritage of the instrument development to cite the Pepin (1969)
report that first documented the technique, and the Rosen et al. (1969) which shows (Figure 4)
the only peer-reviewed paper showing the initial application of the methods to balloon-borne
solar extinction measurements, and later further developed for application to the first satellite
measurements of the stratospheric aerosol layer (the SAM, SAM-II, McCormick et al., 1979),
and then SAGE, SAGE-II and SAGE-III series of satellite measurements.SR9) Section 2, line 76-78
Add ", at wavelength $\lamda$, " after "The aerosol extinction" and add subscript
lamda symbol to the two wavelength-dependent symbols in equation 1 (sigma and AR).In addition, please change the abbreviation "AE" for aerosol extinction, as this may
initially confuse some readers, given the related size-associated aerosol metric
"Angstrom exponent". Please change all occurrences of "AE" instead to either "k"
(used in the Bourassa et al. (2007, 2008) papers) or other terminology
(the letter b is used, subscript "ext" to denote aerosol extinction in
Seinfeld & Pandis (2006).It also needs to be stated explicitly that these calculations are based on an assumed log-normal
size distirbution, with also the associated water content (sulphuric acid and water composition).As explained in General Comment GC2, please delete the two short sentences lines 77-78 as this
statement does not follow from what is shown. The information and associated assumptions are
explained within context in the Bourassa et al. (2007,2008) papers.SR10) Section 2, lines 82-83
As mentioned in General Comment GC2, the text "...but as the two wavelengths approach each other"
is too colloquial and needs to be formalised. Also, the "Any two distinct wavelengths can
be chosen" at the start of the sentence also does not need to be stated. Suggested re-structuring
to better explain the issue.Suggest to re-word the original text:
"Any two distinct wavelengths can be chosen for CR, but as the two wavelengths approach each other
Fig. 1a shows that the CR gradient decreases and thus the uncertainty in the retrieved
size increases."instead to
"For OMPS-LP wavelengths closer to the reference 869nm wavelength, the gradient in the colour
ratio curve is less steep, causing an increased uncertainty in the retrieved particle size."It is worth noting also that the 869nm aerosol extinction measurement is "cleanest" retrieval
in relation to effects from other species, and this must also be considered in relation to
how the errors/uncertainty differ between different color-ratio wavelength-pairs.SR11) Figure 1 caption, lines 431-435.
Although it is not stated explicitly, my understanding is that these calculations are based
on a log-normally distributed aerosol, with geometric standard deviation of 1.6, following
the specification within SASKTRAN. This should be stated in the caption to Figure 1.SR12) Section 2, line 368 -- formatting error re: Loughman et al. (2015) reference.
References
----------Bourassa et al. (2007) Stratospheric aerosol retrieval with OSIRIS limb scatter measurements,
J. Geophys. Res., 112, D10 217, https://doi.org/10.1029/2006JD008079.Bourassa et al. (2008) Retrieval of stratospheric aerosol size information from OSIRIS
limb scattered sunlight spectra, Atmos. Chem. Phys., 8, 6375–6380,
https://doi.org/10.5194/acp-8-6735-2008.James et al. (2023) The importance of acid-processed meteoric smoke relative to meteoric
fragments for crystal nucleation in polar stratospheric clouds
Atmos. Chem. Phys., 23, 2215–2233, https://doi.org/10.5194/acp-23-2215-2023Khaykin et al. (2021) "The 2019/20 Australian wildfires generated
a persistent smoke-charged vortex rising up to 35 km altitude"
Comms. Earth Env., https://doi.org/10.1038/s43247-020-00022-5McCormick et al. (1978) Satellite studies of the stratospheric aerosol
Bulletin of Amer. Meteorol. Soc., vol. 60, no. 9, 1038-1046.
https://doi.org/10.1175/1520-0477(1979)060<1038:SSOTSA>2.0.CO;2Muser et al. (2020) Particle aging and aerosol–radiation interaction affect
volcanic plume dispersion: evidence from the Raikoke 2019 eruption,
Atmos. Chem. Phys., 20, 15015–15036, https://doi.org/10.5194/acp-20-15015-2020Pepin T. J. (1969) "The Use of Extinction from High Altitude Balloons as a Probe
of the Atmospheric Aerosols", Univ. Minn. progress report, Oct, 1969
https://apps.dtic.mil/sti/pdfs/AD0696527.pdfPepin, T. J. (1977) "Inversion of solar extinction data from the Apollo-Soyez test project
Stratospheric aerosol measurement (ASTP/SAM) experiment", volume 1, 529-544, NASA report SP-442.
https://ntrs.nasa.gov/citations/19780009145Rosen, J. M. (1969) "Stratospheric dust and its relationship to the meteoric influx",
Space Science Reviews, vol. 9, 58-89, https://doi.org/10.1007/BF00187579 (see Figure 4).Schneider et al. (2021) " Aircraft-based observation of meteoric material in
lower-stratospheric aerosol particles between 15N and 68N", Atmos. Chem. Phys.,
vol. 21 989-1013, https://doi.org/10.5194/acp-21-989-2021Seinfeld and Pandis (2006)
Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 2nd Edition, Wiley publisher.
John H. Seinfeld, Spyros N. PandisVernier et al. (2016) "In situ and space-based observations of the Kelud volcanic plume:
The persistence of ash in the lower stratosphere", J. Geophys. Res., vol. 121,
11,104–11,118, http://doi.org/10.1002/2016JD025344.Citation: https://doi.org/10.5194/amt-2023-36-RC2 -
RC3: 'Reply on RC2', Anonymous Referee #2, 22 Apr 2023
There seems to be glitch with the electronic journal re-formatting this review, with
strange double-spacing added when it appeared in the mobile-accessible format.
I had this previously with a review I submitted, with it appearing fine when I reviewed it
to approve it at the "Submit" option.
I am attaching a file here with PDF of the review, and this should then be easier to read.- AC3: 'Reply on RC2', Yi Wang, 15 Jun 2023
-
RC3: 'Reply on RC2', Anonymous Referee #2, 22 Apr 2023
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