the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Aug 2024
Evidence of an Ozone Mini-Hole Structure in the Early Hunga Plume Above the Indian Ocean
Abstract. On 15 January 2022, the Hunga volcano (20.5° S, 175.4° E) erupted, releasing significant amounts of aerosols, water vapor (H2O) and a moderate quantity of sulfur dioxide (SO2) into the stratosphere. Due to the general stratospheric circulation of the southern hemisphere, this volcanic plume traveled westward and impacted the Indian Ocean and Reunion (21.1° S, 55.5° E) a few days after the eruption. This study aims to describe current observations of an ozone mini-hole in the first week following the eruption. The Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) aerosol extinction profiles were used to investigate the vertical and latitudinal extension of the volcanic plume over the Indian Ocean. The volcanic aerosol plume was also observed with an aerosol lidar and a sun-photometer located at Reunion. The impact of this plume on stratospheric ozone was then investigated using the Microwave Limb Spectrometer (MLS) and Infrared Atmospheric Sounding Interferometer (IASI) ozone profiles and total ozone maps. Results show that the volcanic plume was observed over Reunion at altitudes ranging from 26.8 to 29.7 km and spanned more than 20 degrees of latitude on 22 January while over the Indian Ocean. Ozone maps reveal an ozone mini-hole structure, with a maximum Total Column Ozone (TCO) anomaly of -38.97 ± 25.39 DU from IASI on 21 January. The MLS profiles impacted by the Hunga water vapor plume show an average ozone anomaly of -0.43 ppmv with a standard deviation of 0.66 ppmv at the 14.68 hPa pressure level.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2024-2350', Anonymous Referee #1, 29 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2350/egusphere-2024-2350-RC1-supplement.pdf
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AC1: 'Reply on RC1', Tristan MILLET, 13 Dec 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2350/egusphere-2024-2350-AC1-supplement.pdf
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AC1: 'Reply on RC1', Tristan MILLET, 13 Dec 2024
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RC2: 'Comment on egusphere-2024-2350', Anonymous Referee #2, 19 Oct 2024
This paper reports an ozone mini hole over the Indian Ocean a few days after the Hunga eruption. First, the authors examine the aerosol extinction anomaly above Réunion from January 17-22, using OMPS data. They then compare different datasets (MLS, DIAL, SIOZ, and IASI). Finally, the ozone anomaly over Réunion is presented, and its attribution to the Hunga eruption is demonstrated using a back-trajectory model. The topic is well-aligned with the scope of ACP. The aerosol extinction analysis is convincing, showing that aerosols from Hunga passed over Réunion around January 22.
However, my main concern is the novelty of the paper. Several studies have already investigated the short-term effects (within the first 10 days) of the Hunga eruption over the Indian Ocean, including aerosol extinctions (e.g., Baron et al. (2023)), ozone anomalies (e.g., Evan et al. (2023)), and detailed chemical analyses (e.g., Zhu et al. (2023)). The authors need to clearly highlight how their work extends beyond the scope of these existing studies. I am concerned about the lack of new scientific insights presented in this paper. Therefore, I recommend resubmission or major revision before the manuscript can be considered for publication. Significant changes are required to address both the concerns outlined below and the issue of novelty.
Major comments:
- The authors present background ozone profiles from different months observed by DIAL and explain the variations in altitude with the highest ozone concentrations in Section 3.2. However, this section seems less relevant to the main topic. Additionally, Figure 3 is not particularly informative, as it merely displays typical tropical ozone concentrations in an altitude-month contour.
- The MLS and IASI data are well-validated and widely used in the ozone community, so it may be unnecessary to validate them in this paper. However, it's not a negative addition. Besides, the standard deviation calculation in Figure 4a is inappropriate. The authors calculate the standard deviation for the mean relative bias, which decreases as the number of samples increases. Instead, they should calculate the standard deviation for the relative bias itself (as done in Figure 6), which would represent the variation of each individual relative bias.
In Section 3.4, the authors report the ozone anomaly. While I believe this finding is valid, as many previous studies have already demonstrated it, the results and discussions presented here are not convincing.
- The biggest issue is with Figure 5 and its description: SO2 is not a reliable tracer for volcanic gases and particles. As the authors themselves mention, "the rapid conversion of SO2 molecules to sulfate particles" occurs. Therefore, there are two distinct possibilities for a region with low SO2 concentrations: (1) volcanic gases and particles did not reach this region, or (2) volcanic gases and particles did reach the region, but the SO2 was converted to sulfate. These two possibilities are entirely different and need to be clearly distinguished.
- The authors mention a "correlation between ozone, H2O, and SO2." While the correlation between H2O and SO2 is visible, the correlation between ozone and the other two gases is unclear in Figure 5. In addition, the significant ozone anomaly (shown in blue) appears throughout the region, even before the Hunga aerosol transport (e.g., Figure 5 b1, b2), making it difficult to attribute the ozone anomaly specifically to the Hunga eruption.
- The largest correlation between ozone and water vaper is -0.68 in Figure 6c, which is not significant.
Minor comments:
- In the abstract, introduction and conclusion, the authors state that “Hunga volcano eruption released significant amounts of aerosols, water vapor (H2O) and a moderate quantity of sulfur dioxide (SO2) into the stratosphere.” However, volcanoes rarely release aerosols directly. Instead, sulfate aerosols form from the oxidation of SO2.
- Line 20: The term “halons (Br)” is vague. Halons are not equal to Br, so further explanation is needed. For example, it could be revised to “halons (including Br)”.
- Line 28: The capitalization of "Volatile Organic Compounds" is unnecessary.
- Line 34: See my first minor comment.
- Some abbreviations are not explained. For example, "PSC" at Line 50 and "QBO" at Line 64 should be defined upon first use.
- Line 315: The phrase "altitude level, date, and time" is vague. Do you mean the time of day?
- Figure 4: The statement "p-value = 0.0" is not meaningful in this context. The authors should either remove the p-value or provide a more meaningful value in Figure 4.
- Line 346: The unit of "DU" seems strange for SO2.
Citation: https://doi.org/10.5194/egusphere-2024-2350-RC2 -
AC2: 'Reply on RC2', Tristan MILLET, 13 Dec 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2350/egusphere-2024-2350-AC2-supplement.pdf
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RC3: 'Comment on egusphere-2024-2350', Anonymous Referee #3, 24 Oct 2024
The paper is good, with some new analysis regarding the other previous papers. I recommend accepting the paper with major revision which gives improvement for better understanding some parts. Below, there are general considerations and, after, the corrections by lines.
Several papers were cited by the authors which analyzed the Hunga volcanic eruption and its influences. The authors should describe better their contributions on the ozone study after the passage of Hunga plumes. What is the difference for this work with the others? The objective of the paper is not very clear.
In the Introduction, the chemical influence of chlorine and sulfur compounds in ozone should be discussed further with showing some chemical reactions. After all, the objective of the paper is to show the influence of the volcanic plume on atmospheric ozone.
In the methodology, it should be explained what location (latitude, longitude, grid used for satellite data, …) the paper analyzed. This should be put in the beginning. The methodology should be expanded to explain better the instruments and the methodology used.
In item 2.1 - Ozone Measurements, for better understanding the work, it is needed to create separate subtitles to describe each instrument, their data and its problems with the Hunga plume.
In the results part, it is important to change Figure 5. How it showed the ozone total column and ozone anomaly. It was not possible to see the reduction discussed in the paper based only in this figure.
L.16: why cited WMO (2018) and not WMO (2022)?
L. 17: a reference for the ozone absorbing range must be cited
L. 20 – 21: The authors wrote “In the past decades…”, however the only reference cited is from 1996.
L. 15 – 29: The text should be separated in two paragraphs for a better understanding in stratospheric ozone and tropospheric ozone.
L. 30 – 41: In this part, the authors described the influence of some volcanic eruptions on ozone. However, only two are cited. They were important eruptions, but other eruptions and new studies should be analyzed also. Calbuco was only cited in line 52.
L. 63 – 64: “As a result of the main austral summer stratospheric circulation and the prevalent phase of the QBO…” – Explain better this main circulation and what phase of QBO were acting in the period analyzed.
L. 83 – 84: Explain “the remaining aerosol plume consisted of two concentrated patches”
L. 94 – 96: What kind of observations were described in the paper? What species were analyzed from satellite and ground-based observations?
L. 100 – 103: It is not necessary.
L. 147: “The maximum 1σ standard deviation found in the stratosphere was close to 0.05 ppmv”. What is the mean ozone mixing ratio for this region? How much percentage it represents?
L. 153: The “established criterion” is not clear.
L. 211: What is the lat, lon for the location of Saint-Denis?
L. 231: What is the location of the lidar site? Lat, lon.
L. 255: Describe first what panel (a) in Figure 1 represents.
L. 309-316: In Fig. 4 were described two kinds of data. In this paragraph, the analysis was confused. Please, rewrite it.
L. 322: Define SNR.
L. 333: Standardize RMSD or RMSE.
L. 345: “All maps are overlaid with blue contours of the SO2 plume…”. It should be red contours, not blue.
L. 354: How could be seen “222.87” DU if the figure scale begins in 240 DU? Figure 5 needs to change the data range from legend and colors pattern, because it was impossible to see the reduction in ozone total column and the anomalies showed by the red areas.
L. 352 – 371: Where is the data from this paragraph? It was not possible to see the number cited based on Fig 5.
L. 701: For Zhu et al. (2023), it should be cited as the doi for final version of the paper, not the preprint doi. The correct doi is: https://doi.org/10.5194/acp-23-13355-2023.
Citation: https://doi.org/10.5194/egusphere-2024-2350-RC3 -
AC3: 'Reply on RC3', Tristan MILLET, 13 Dec 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2350/egusphere-2024-2350-AC3-supplement.pdf
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AC3: 'Reply on RC3', Tristan MILLET, 13 Dec 2024
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