The Typical ELF/VLF Electromagnetic Wave Activities in the Upper Ionosphere Recorded by the China Seismo-Electromagnetic Satellite

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper introduces the typical electromagnetic waves mainly in the ELF/VLF band recorded by the CSES-01. Their analysis indicates that typical and common natural EM waves in the ionosphere mainly include ionospheric hiss and proton whistlers in the ELF band, the quasiperiodic emissions, magnetospheric line radiation, falling-tone lightning whistlers and V-shaped streaks in the ELF/VLF band. The research objective of this article is clear and the content is substantial. However, in my personal view, there are some points need to be further improved, which are provided as follows. These comments are just given to the authors for reasonable consideration.

(1) ELF/VLF and EM should have their full names at least once at the beginning.

(2) The keyword “wave vector analysis” does not appear in the abstract. In the abstract, only “ionosphere” appears instead of the keyword 'the upper ionosphere'.

(3) It is better to break down the sentence from lines 45 to 47 into two sentences, or use “which” to connect them.

(4) The introduction is too long and the focus of the article is not prominent.

(5) The image style should be consistent. Some horizontal coordinates in the article use magnetic latitude, while others use longitude and latitude.

(6) The introduction about CSES is repeated, lines 59-62 and 127-130.

(7) Line 60, it should be “China Seismo-Electromagnetic Satellite”.

(8) There is no need to include abbreviations in parentheses for content that does not appear in the following text, such as LAIC. Even if used, it should be before the “mechanism”.

(9) The introduction to the 8 types of scientific payloads carried by CSES may not be a major concern and may be omitted.

(10) The ULF in line 157 should have a full name.

(11) Line 160, the “widely applied” SVD only has one reference.

(12) In Figure 1, there is no red arrow mentioned in line 208, although there is a red high-frequency component inside the black rectangles.

(13) The labeling in Figure 3 is not clear, it is recommended to replace the color code. If Figure 3 is replaced, the other images should also remain consistent.

(14) This article should be a research article, but it reads like a review article. If it is not a review article, the research results of others do not need to be elaborated in detail, such as lines 561-575.

(15) Lines 528, it should be “Viking[63] and FAST[64] satellite”.

(16) The word “artificial sources in the lithosphere” is inappropriate, and references 16 and 65 cited do not mention the term “lithosphere”. Therefore, lines 535, 540 and 619 need to be changed.

(17) The chapter name should be set at the corresponding directory level.

(18) The section 5 “Discussion and Conclusion” is too long. It is recommended that the discussion be placed in the main text, and this section should focus on summarizing your findings and research content. Therefore, this section can be changed to “Conclusion and Outlook”.

(19) The format of the references is too messy and should be consistent with the journal.

Comments on the Quality of English Language

The English is written very well.

Author Response

(1) ELF/VLF and EM should have their full names at least once at the beginning.

Revised. See Line 70.

(2) The keyword “wave vector analysis” does not appear in the abstract. In the abstract, only “ionosphere” appears instead of the keyword 'the upper ionosphere'.

Thank you for your comments. We have revised the abstract accordingly，see lines 25-27.

(3) It is better to break down the sentence from lines 45 to 47 into two sentences, or use “which” to connect them.

Thank you for your suggestion. We have revised lines 45 to 47 by splitting them into two sentences for improved clarity and readability, see line 45.

(4) The introduction is too long and the focus of the article is not prominent.

We appreciate your suggestion on the introduction’s length and focus. We have removed excessive descriptions of the satellite to clarify the structure of the introduction. The opening section highlights the complexity of the ionospheric system and the importance of studying the ionospheric electromagnetic environment for human activities. The middle section summarizes previous research on ionospheric electromagnetic waves. In the final part, we present the research questions, specifically focusing on extracting the electromagnetic disturbances we are concerned with in a complex space environment, see the introduction.

(5) The image style should be consistent. Some horizontal coordinates in the article use magnetic latitude, while others use longitude and latitude.

Thank you for your observation regarding the consistency of coordinate systems in our figures. We have revised all figures to consistently use geographic latitude and longitude across all images to ensure uniformity in data presentation.

 

(6) The introduction about CSES is repeated, lines 59-62 and 127-130.

We have removed this section from the introduction.

(7) Line 60, it should be “China Seismo-Electromagnetic Satellite”.

Revised.

(8) There is no need to include abbreviations in parentheses for content that does not appear in the following text, such as LAIC. Even if used, it should be before the “mechanism”.

Revised.

(9) The introduction to the 8 types of scientific payloads carried by CSES may not be a major concern and may be omitted.

Thank you for your suggestion about the detail on the scientific payloads carried by CSES. We have omitted the extensive details about the eight types of scientific payloads from the manuscript to focus more on those directly relevant to our study. 

(10) The ULF in line 157 should have a full name.

Revised, see line 124.

(11) Line 160, the “widely applied” SVD only has one reference.

We’ve added more references to support the claim that SVD is “widely applied.” See lines 127-128.

(12) In Figure 1, there is no red arrow mentioned in line 208, although there is a red high-frequency component inside the black rectangles.

Revised, see line 175.

(13) The labeling in Figure 3 is not clear, it is recommended to replace the color code. If Figure 3 is replaced, the other images should also remain consistent.

We have changed the label colors in Figure 3 to improve clarity. See the updated Figure 3.

(14) This article should be a research article, but it reads like a review article. If it is not a review article, the research results of others do not need to be elaborated in detail, such as lines 561-575.

Thank you for your suggestion. We have removed the detailed descriptions of other studies from lines 561-575 to better emphasize our own research findings.

(15) Lines 528, it should be “Viking[63] and FAST[64] satellite”.

Revised, see line 481.

(16) The word “artificial sources in the lithosphere” is inappropriate, and references 16 and 65 cited do not mention the term “lithosphere”. Therefore, lines 535, 540 and 619 need to be changed.

Revised, see lines 488,492 and 651

(17) The chapter name should be set at the corresponding directory level.

Revised.

(18) The section 5 “Discussion and Conclusion” is too long. It is recommended that the discussion be placed in the main text, and this section should focus on summarizing your findings and research content. Therefore, this section can be changed to “Conclusion and Outlook”.

We appreciate the recommendation to refine the structure of our paper. We have reorganized the content by integrating the detailed discussion into the main text and refocusing Section 5 on summarizing our findings and future outlook. The section has been renamed to “Conclusion and Outlook” accordingly.

(19) The format of the references is too messy and should be consistent with the journal.

We have corrected the reference formatting throughout the manuscript to align with the journal’s standards.

 

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents typical phenomena of natural or artificial electromagnetic activities in the ELF/VLF range. They come from 5 years of measurements from the CSES-01 satellite transiting through the ionosphere in an orbit at an altitude of 507 km. The spectral and wave propagation properties are calculated by the SVD method. An abundant bibliography (71 references) makes it possible to interpret the observations in relation to the conclusions obtained by previous satellite missions. The authors conclude on the need to pursue new experimental missions (CSES-02) to better explain the generation and propagation of the observed phenomena.
I do not propose any correction to the proposed text which is well constructed.

Author Response

The paper presents typical phenomena of natural or artificial electromagnetic activities in the ELF/VLF range. They come from 5 years of measurements from the CSES-01 satellite transiting through the ionosphere in an orbit at an altitude of 507 km. The spectral and wave propagation properties are calculated by the SVD method. An abundant bibliography (71 references) makes it possible to interpret the observations in relation to the conclusions obtained by previous satellite missions. The authors conclude on the need to pursue new experimental missions (CSES-02) to better explain the generation and propagation of the observed phenomena.
I do not propose any correction to the proposed text which is well constructed.

Thank you for your positive feedback and for acknowledging the structure and content of our paper. We appreciate your recognition of the efforts we made in analyzing the data from the CSES-01 satellite and discussing its implications in the broader context of electromagnetic studies in the ionosphere. We are also committed to continuing this line of research with future missions to further our understanding of these phenomena.

Reviewer 3 Report

Comments and Suggestions for Authors

The paper: The typical ELF/VLF electromagnetic wave activities in the upper ionosphere recorded by the China Seismo-Electromagnetic Satellite, ID remotesensing-3068355

Authors: Yunpeng Hu, Zeren Zhima, Tieyan Wang, Chao Lu, Dehe Yang, Xiaoying Sun, Tian Tang, Jinbin Cao

 

This is very interesting and useful paper accumulating the experimental data on ELF and VLF EMW (electromagnetic wave) field measured by the China Seismo-Electromagnetic Satellite. The general idea includes the using these data and their interpretation for the understanding the mechanisms of the coupling in Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). At the same time for a full disclosure of the topic of this work, I propose to make the minor revision and then paper may be published. Please make the additions/improvements in the text of the paper, corresponding to the questions/note listed below.

(1)    Please stay more on the data demonstrating an upward propagation of VLF waves, which hypothetically may be connected with seismic activity in spite of some of the corresponding references, such as [33], are included in the paper. More detail description of the known results concerning possible seismogenic emissions, detectable, in principle,  on satellites/ CSES should be given.

(2)    The distinguishing between corresponding VLF and ELF emissions and the known conditions of their detectability, in particular on the board of CSES (01 and/or 02) should be discussed, for the benefits of the readers of “Remote Sensing”.

(3)    Only hiss emissions are mentioned in connection with seismoionospheric coupling. Whether there are satellite data on possible ELF/VLF seismogenic data/LAIC coupling of other types?

(4)    In the discussion of quasi-periodical (QP) pulsations, two mechanisms are discussed: (i) modulation of ELF/ULF waves by geomagnetic ULF pulsations; (b) wave-particle interaction with cyclotron plasma instability. It is worth to add the third possible mechanism connected with possible seismoionospheric coupling. In particular, ELF wave modulated by ULF inside the Earth crust/n the lower atmosphere may be also mentioned, and this is the possible mechanism of the penetration to the ionosphere of the combined ELF/VLF-ULF perturbations “from below” [V. Grimalsky, Yu Rapoport, M. Tecpoyotl-Torres, O. Ivantyshyn, A. Nesterenko, Nonlinear frequency down-conversion of acoustic wave beams in the atmosphere and ionosphere under different types of modulation, J. Atmos. Solar-Terrestr. Phys., V. 227

,2022, 105774, https://doi.org/10.1016/j.jastp.2021.105774].

(5)    You have mentioned earthquakes as possible sources of electromagnetic emissions detectable at the boards of satellites. It is worth to mentioned that among the corresponding powerful sources in the lower atmosphere/Earth providing electromagnetic coupling in the Earth-Atmosphere-Ionosphere system, tropical cyclones and volcano should be mentioned as well.

(6)    The paper is well-structured in principle. Nevertheless, to finalize this structurization,  it is necessary to make the pronounce conclusions either is the section Discussion and Conclusions or in a separate Conclusion section (the last option is preferable).

Finally, the paper may be published after the minor revision, as described above.

Author Response

(1) Please stay more on the data demonstrating an upward propagation of VLF waves, which hypothetically may be connected with seismic activity in spite of some of the corresponding references, such as [33], are included in the paper. More detail description of the known results concerning possible seismogenic emissions, detectable, in principle,  on satellites/ CSES should be given.

Thank you for your comments. The hiss presented in this manuscript originate from the plasmasphere. We further discuss earthquakes as a potential source of ionospheric hiss waves, as described in Section 604-609. However, due to the complexity of directly linking earthquake events to hiss and the lack of conclusive observational evidence, we will conduct a more detailed analysis in future work.

(2) The distinguishing between corresponding VLF and ELF emissions and the known conditions of their detectability, in particular on the board of CSES (01 and/or 02) should be discussed, for the benefits of the readers of “Remote Sensing”.

Thank you for your suggestion. We have now included a brief description of the characteristics of ELF and VLF emissions in the manuscript, see lines 626-636.

(3) Only hiss emissions are mentioned in connection with seismoionospheric coupling. Whether there are satellite data on possible ELF/VLF seismogenic data/LAIC coupling of other types?

Thank you for highlighting the scope of our discussion on seismoionospheric coupling. While this manuscript primarily addresses hiss emissions, we acknowledge the importance of exploring other types of ELF/VLF emissions related to seismoionospheric activities. We will consider expanding our analysis to include additional types of ELF/VLF seismogenic data in future studies to provide a more comprehensive overview of LAIC (Lithosphere-Atmosphere-Ionosphere Coupling) phenomena.

(4)    In the discussion of quasi-periodical (QP) pulsations, two mechanisms are discussed: (i) modulation of ELF/ULF waves by geomagnetic ULF pulsations; (b) wave-particle interaction with cyclotron plasma instability. It is worth to add the third possible mechanism connected with possible seismoionospheric coupling. In particular, ELF wave modulated by ULF inside the Earth crust/n the lower atmosphere may be also mentioned, and this is the possible mechanism of the penetration to the ionosphere of the combined ELF/VLF-ULF perturbations “from below” [V. Grimalsky, Yu Rapoport, M. Tecpoyotl-Torres, O. Ivantyshyn, A. Nesterenko, Nonlinear frequency down-conversion of acoustic wave beams in the atmosphere and ionosphere under different types of modulation, J. Atmos. Solar-Terrestr. Phys., V. 227

,2022, 105774, https://doi.org/10.1016/j.jastp.2021.105774].

Thank you for the suggestion. We have added a discussion of the third mechanism involving seismoionospheric coupling, see lines 610-620.

(5)    You have mentioned earthquakes as possible sources of electromagnetic emissions detectable at the boards of satellites. It is worth to mentioned that among the corresponding powerful sources in the lower atmosphere/Earth providing electromagnetic coupling in the Earth-Atmosphere-Ionosphere system, tropical cyclones and volcano should be mentioned as well.

As you suggested, we have mentioned other sources of electromagnetic emissions in lines 41-42. Since the events observed in this paper do not involve these sources, they are not discussed further."

(6)    The paper is well-structured in principle. Nevertheless, to finalize this structurization,  it is necessary to make the pronounce conclusions either is the section Discussion and Conclusions or in a separate Conclusion section (the last option is preferable).

Thank you for your suggestion. We have created a separate 'Conclusion and Outlook' section to clearly present the main conclusions and future directions of our study.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no any more comments about the revised manuscript now.