Clues of Lithosphere, Atmosphere and Ionosphere Variations Possibly Related to the Preparation of La Palma 19 September 2021 Volcano Eruption

Round 1

Reviewer 1 Report

Please see the attached file.

Comments for author File: Comments.pdf

Author Response

Thank you so much for your great suggestions and help to improve our manuscript!

Please find in attach a reply point-by-point to your valuable suggestions and questions!
Thank you a lot!

Author Response File: Author Response.pdf

Reviewer 2 Report

Brief summary:

The manuscript investigates time series data, which describe seismicity in the lithosphere, concentrations of several gases in the atmosphere, and electron density in the ionosphere, before a volcano eruption in La Palma. Co-occurring anomalies between the data sets are found which complement previous studies in the area.

General comments:

The manuscript is well organized, clearly written with enough details, and technically mostly correct. The figures are illustrative, possible explanations for the observations are discussed, and the conclusions are justified. Minor suggestions to improve the manuscript are given below.

Detailed comments:

Line 54: Please write out all acronyms when they appear the first time. TEC appears the first time on line 54 but the explanation appears not until on line 86.

Section 1: Please include the organization of the paper and highlight the novelty of the paper at the end of Section 1.

Line 206: "Ne" has not been defined (although it is quite well-known).

Line 229: "kt" has not been defined.

Line 253: "a 90% of probability" should be "90% probability".

Figure 3a: The units of the longitude and latitude axes are missing from the plot. They are also missing from the images in Figs. 5, 7, 9, 11, and 12.

Figure 4: Please mention the extent of the geographical area (latitude and longitude ranges) within which the time series data have been taken. Is it the same area as shown in Fig. 5 or a smaller area containing only La Palma? The extent of the area is missing also for data presented in Figs. 6, 8, and 10.

Lines 328-330: The resolution of the SO_2 image in Fig. 5A is so low that it is questionable to state that the maximum coincides with Cumbre Vieja.

Line 331: Does "Eastern plume" mean that it is located to the east from La Palma? In Fig. 5, it is to the west from La Palma.

Lines 336-337: Can there be other sources than volcanic? "Conforming its volcanic source" may be too much to say. "Suggesting its volcanic source" may be better.

Figure 7: There are no white stars in the images (or one cannot see them anyway) unlike stated in the caption.

Figure 8: Total aerosol extinction has not been defined. AOT would range from zero to infinity.

Figures 5, 7, 9, and 11: The subfigures in each of these figures would be easier to compare if the ranges in the colorbars were the same in all subfigures of each figure (which can be achieved using clim or caxis in matlab).

Line 464: It is mathematically inexact to express the radius of a circle by an angle.

Lines 465-467 and Figs. 18 and 19: There are confusions between the trend, residual, and median. It reads "trend" on line 466, but the trend has been removed in the figures. The figures are titled "residual of median daily values", but they are "median of residual daily values". The figure captions should also remind that the daily values have been detrended.

Line 482: "analyse the closer orbit" does not make sense, because the orbit is exactly the same every five days. Do you mean "analyse the closest orbit" or "analyse the data captured in the orbit more closely"? Or are the day-time and night-time orbits different so that the night-time orbit is closer than the day-time orbit? 

Line 485: "two orbits" should be "two passes" (in the same orbit).

Lines 501-502: "surrounding" does not include the area inside it. Do you mean "containing"?

Figure 23 caption: Pinatubo volcano eruption was on 12 June and not on 12 July.

Lines 647-651 and 288-300: The depths of the earthquakes (from 40 km upwards) and the depth of the deep magmatic chamber (13-20 km) given in the conclusions do not match with the depths (from 50 km upwards and around 30 km) given in Section 3.1. 

Author Response

Thank you so much for your very good suggestions and help to improve our manuscript!

Please find in attach a reply point-by-point to your valuable suggestions and questions!
Thank you a lot!

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments on “Lithosphere, Atmosphere and Ionosphere coupling in the preparation of La Palma 19 September 2021 volcano eruption” by Marchetti et al.

The authors studied the changes in seismicity, atmospheric parameters (SO2, DMS, Aerosol, and CO), and ionospheric density of CSES and geomagnetic field of SWARM satellites six months before the eruption of the La Palma Cumbre Vieja Volcano on 19 September 2021. The authors identified a temporal migration of the seismicity and attributed that to the magma migration. The authors show an increase of Carbon Monoxide 1.5 months before the eruption and suggest the last uplifting of the magma. The authors further showed that the satellite CSES-01 detected an increase in electron density and suggested an electromagnetic coupling between the lithosphere and ionosphere. The authors also stated that the atmosphere and ionosphere showed anomalies from more than three months until two months before the eruption suggesting a coupling between them.

The major gaps in this study are: (1) Missing the description and illustration of the analysis of the seismicity, CSES electron density, and SWARM magnetic field data. (2) The evidence of the connection between the atmosphere and the ionosphere is missing. (3) The solar activity was not considered accurately. (4) The coupling mechanism is confusing. Accordingly, the reviewer cannot recommend the manuscript be considered by the journal.

Major comments:

(1) The authors showed the analysis of the atmospheric parameters (SO2, DMS, Aerosol, and CO) step by step (Figures 4 to 17). The reviewer satisfies the evidence of the changes in the atmospheric parameters before the eruption.

However, the authors did not show the analysis of the seismicity and the cumulative Benioff Strain step by step. Showing only the curve of the cumulative value (Figure 3c and Figure 24) without the raw seismicity time series and analysis process cannot convince the audience. The authors show the raw data of seismicity first, at least. On the other hand, the authors did not show the analysis of CSES-01 Ne (Figures 18 and 19) and SWARM magnetic field (Figures 21 and 22) in detail either. The authors should show the raw data and the analysis step by step.

(2) The changes in the atmospheric parameters (SO2, DMS, Aerosol, and CO) are in the troposphere. The atmosphere can affect the ionosphere, but the authors did not show the connection. How come the authors connect the changes in the troposphere to the ionosphere? In other words, if there is a connection between the atmospheric and the ionospheric parameters before the eruption, the authors should show evidence of atmospheric gravity waves or tidal waves in the mesosphere and thermosphere.

(3) Lines 501 to 528, the authors did not show the raw magnetic data and the detail of the analysis process. What’s the statistical significance of the possible anomaly? A track of magnetic changes (Figure 22) and the processed values cannot convince the audience that the changes relate to the volcano. There are ground-based magnetometers (i.e., station GUI) near the volcano (https://www.intermagnet.org/index-eng.php). The authors should include the analysis of the time series of the ground-based magnetic field near the volcano to verify the SWARM result.

 (4) The ionospheric changes are not solid. Dst indicates the changes of the ring current in the plasmasphere rather than the change in the ionosphere. The authors should use the AE index for the quiet time threshold. The AE values are large on 22 July 2022 (https://wdc.kugi.kyoto-u.ac.jp/ae_realtime/202107/index_20210722.html). The electromagnetic changes from the polar region are significant. The authors should carefully consider solar activity. The ground-based GNSS total electron content is an openly available parameter (http://cedar.openmadrigal.org/openmadrigal) to verify the CSES Ne and the effect of solar activity.

(5) "Coupling” means the interaction between two phenomena. The authors also mentioned in conclusion: “This paper analyzed the lithosphere, atmosphere and ionosphere and their possible interactions.”

The authors show that the lithosphere changes possibly affect the atmosphere or ionosphere. However, here is no evidence to show the effect of the atmosphere on the lithosphere or the ionospheric effect on the atmosphere. In other words, do the changes in the upper spheres feed back to the lower spheres in this study? Using the term “coupling” in this study is not proper. The title, description, and discussion statements show be modified.

Minor comments:

Lines 34 to 37: “…..several models, and multiple observations support their existence, even if definitive proof is still missing ….” References are required for the statement.

Line 38: “…evidence statistically proves such phenomena…”  References are required.

Line 42: “…. satellites in Low Earth Orbits (LEO) …” References are required.

Line 45: “… Geostationary satellites …” References are required.

Lines 51 to 61:  The authors studied phenomena before the eruption. The authors did not study the acoustic or gravity waves after the eruption. This paragraph is irrelevant to this study, and it should be removed from the manuscript.

108 to 111: According to the logic here, the authors should study the Tonga event. The Tonga volcano eruption is beneath the ocean surface, which differs from the La Palma volcano. The statements should be modified.  

Lines 164 to 166: Solar irradiation does not change the troposphere significantly above the boundary layer. The statements should be modified.

Line 185: What's the reason for the specific values of 248 days to 531 days? A reference is required.

Line 205: It is unfair to use the different fitting values for day and night. The nighttime ionosphere can be much more complicated than the daytime ionosphere, and reference is required for the fitting values.

Line 225: A reference is required for fitting the magnetic data.

Author Response

Dear reviewer,

Thank you so much for your very good suggestions and questions that helped us to improve our manuscript! We are sorry, that the first submission didn't convince you, but I agree with you that several points were not well clarified or explained. We provide now a revised version that try to clarify better that the goal of this study is to investigate the lithosphere, atmosphere and ionosphere, but we don't pretend to demonstrate the coupling between them. We propose the coupling as one of the possible interpretations of the detected anomalies, but we are aware (and we wrote explicitly starting from the title) that other interpretations are possible and future studies are necessary to demonstrate the coupling.

We integrated the parameters (ground magnetic data and TEC) that you requested and they helped a lot to described better and increase the evidence of the detected anomalies. We provided detailed step-by-step descriptions of data processing as well as a Supplementary document with all the Swarm magnetic anomalous tracks. We hope now you can find the manuscript worth of publication, providing some points for the scientific discussion on such phenomena!  

Please find in attach a reply point-by-point to your valuable suggestions and questions!
Thank you a lot! Your suggestions helped a lot in improving the manuscript!

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you to the authors for their wonderful feedback. The article deserves to be published as it is.

Author Response

Thank you so much to you for your wonderful and constructive suggestions that helped to improve a lot the manuscript!

Reviewer 3 Report

The reviewer appreciates that the authors made great efforts in the revision.

Comments on the reviewer’s responses:

(1) If the acoustic-gravity waves (atmospheric waves) are not the main driver of the pre-volcano phenomena, the second paragraph (Lines 57 to 71) is irrelevant to this study, and it should be removed from the manuscript.

(2) The “coupling” standards for the interaction of two spheres at least, which is the two-way effect. However, the authors studied the changes in the bottom (lithosphere) and top (ionosphere), which is a one-way effect rather than a coupling process. The authors did not study the changes from top to bottom, and the authors should remove the term “coupling” from the manuscript.

(3) The mechanism, as shown in Figure 2, is unphysical. Regarding the illustration in Figure 2a, ionization in the lower atmosphere cannot reach the ionosphere. The molecular ion losses instantly in the lower atmosphere due to the dense neutral air particles. For Figure 2b, if the ULF electromagnetic wave propagates in the ionosphere, the plasma drifts (ExB/B2) can record it. The authors should show the drift data from the CSES and swarm satellites. Clarification of the possible physical mechanisms is required.

Author Response

Dear reviewer,

We thank you a lot for your further precious suggestions and indications that helped us still to improve the discussion of the results of this paper.

Following your valuable suggestion, we have provided a preliminary investigation of ion drift from Swarm data that permitted us to confirm our results further. Thank you so much for your very good advice.

Please, found in black bold our reply point-by point.

We hope that now you can find our paper worth publication in Remote Sensing, and we thank you again for your valuable suggestions!

The reviewer appreciates that the authors made great efforts in the revision.

Thank you so much! We are glad you appreciate the effort made in the revision, and we have tried to make all the possible improvements in due time, following your suggestions! Thank you a lot again!

Comments on the reviewer’s responses:

(1) If the acoustic-gravity waves (atmospheric waves) are not the main driver of the pre-volcano phenomena, the second paragraph (Lines 57 to 71) is irrelevant to this study, and it should be removed from the manuscript.

Thank you so much for your comment and suggestion. We have removed this paragraph from the paper and the relative references as requested. We also confirm that we don’t take into account the acoustic gravity wave as a possible pre-volcano phenomenon.

(2) The “coupling” standards for the interaction of two spheres at least, which is the two-way effect. However, the authors studied the changes in the bottom (lithosphere) and top (ionosphere), which is a one-way effect rather than a coupling process. The authors did not study the changes from top to bottom, and the authors should remove the term “coupling” from the manuscript.

Thanks for your comment and suggestion. We have removed the word “coupling” from the manuscript. Anyway, we would remind that this term is widely used to describe these bott-up phenomena in this field. For this reason, we left only one occurrence of the word coupling in the introduction when we cite the model proposed by Pulinets and Ouzounov, 2011, that according to their paper title is “Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) Model – An Unified Concept for Earthquake Precursors Validation.”. Other examples from pioneering experts of this field are the following:

• Liperovsky et al., 2008. Physical Models of Coupling in the Lithosphere-Atmosphere-Ionosphere System before Earthquakes.
• Kuo et al., 2014. An Improved Coupling Model for the Lithosphere-Atmosphere-Ionosphere System.
• Parrot, 2017. Events Linked to the Lithosphere-Atmosphere-Ionosphere Coupling Observed by DEMETER
• Parrot et al., 2021. A. Atmospheric and Ionospheric Coupling Phenomena Associated with Large Earthquakes.
• Pulinets et al., 2022. Atmosphere-Ionosphere Coupling Induced by Volcanoes Eruption and Dust Storms and Role of GEC as the Agent of Geospheres Interaction.

Although I think that the use of the word "coupling" was proper according to the literature, we followed the reviewer’s suggestion removing the "coupling" word from the manuscript. We thank the reviewer who permitted us to clarify that the effects we investigated in the manuscript are bottom-up type as we now specified in the whole manuscript to avoid any possible ambiguity to the reader.

(3) The mechanism, as shown in Figure 2, is unphysical. Regarding the illustration in Figure 2a, ionization in the lower atmosphere cannot reach the ionosphere. The molecular ion losses instantly in the lower atmosphere due to the dense neutral air particles. For Figure 2b, if the ULF electromagnetic wave propagates in the ionosphere, the plasma drifts (ExB/B2) can record it. The authors should show the drift data from the CSES and swarm satellites. Clarification of the possible physical mechanisms is required.

Thank you very much for your comment and suggestion. We have added a new paragraph in the discussion section (4.4) with also two additional figures where we have analysed the ion drift as suggested by the reviewer. We thank the reviewer as this suggestion is very important and permitted to support our previous discussion. We will extend in our future works on a more systematical approach (in this paper, we provided two preliminary examples). In addition to your suggestion, we also calculated the Pointing Vector using the electric field provided by ESA on the measurement of ion drift by Thermal Ion Imager instrument onboard Swarm satellites. For what concern the propagation mechanism of the anomalies, we are aware that the literature that we cited is not universally accepted in the scientific community, and this was already stated in the Introduction section 1.2: “The existence of bottom-up Lithosphere Atmosphere Ionosphere effects before volcano eruptions and earthquakes is a controversial scientific topic.”. The fact that air ionization can produce ionospheric disturbances is supported by several LAIC models, and in particular, we added the citation of the following paper by Sergey Pulinets that explains the Global Electric Circuit (GEC) of Earth supporting this theory that air ionization can induce ionospheric disturbances:

• Pulinets, S.A. Physical Mechanism of the Vertical Electric Field Generation over Active Tectonic Faults. Advances in Space Research 2009, 44, 767–773, doi:10.1016/j.asr.2009.04.038.

We have inserted the above citation to better support the background model in our paper. We fully agree with the reviewer that future studies are required to understand better such lithosphere atmosphere and ionosphere propagation mechanisms. Still, the clarification on such models is beyond the scope of the present paper. On the other hand, we hope that the empirical investigation that we presented in this paper could help the scientific community to improve the above-cited models.

We hope now the reviewer can find the paper worth of publication, and we thank you a lot for the very scrupulous check of our paper that permitted us to improve it and for the valuable suggestions you gave us!