Simulated Long-term Evolution of the Thermosphere during the Holocene: 2. Circulation and Solar Tides

Zhou, Xu; Yue, Xinan; Cai, Yihui; Ren, Zhipeng; Wei, Yong; Pan, Yongxin

doi:https://doi.org/10.5194/egusphere-2023-234

Preprints

https://doi.org/10.5194/egusphere-2023-234

Preprints

15 Feb 2023

| 15 Feb 2023

Simulated Long-term Evolution of the Thermosphere during the Holocene: 2. Circulation and Solar Tides

Xu Zhou, Xinan Yue, Yihui Cai, Zhipeng Ren, Yong Wei, and Yongxin Pan

Abstract. On timescales longer than the solar cycle, long-term changes in CO₂ concentration and geomagnetic field have the potential to affect thermospheric dynamics. In this paper, we investigate the thermospheric dynamical response to these two factors during the Holocene, using two sets of ~12,000-yr control runs by the coupled thermosphere-ionosphere model, GCITEM-IGGCAS. The main results indicate that increased/decreased CO₂ will enhance/weaken the thermospheric circulation throughout the Holocene, but this effect is nonlinear. The cooling effect of CO₂ in the thermosphere further provides plausible conditions for atmospheric tidal propagation and increases the thermospheric tidal amplitude. Geomagnetic variations induce hemispheric asymmetrical responses in the thermospheric circulation. Large changes in the circulation occur at high latitudes in the hemisphere with distant magnetic poles drift, inferring a crucial role of geomagnetic non-dipole variations in circulation changes. A positive correlation between the diurnal migrating tide (DW1) and geomagnetic dipole moment is revealed for the first time. The amplitude of DW1 in temperature will increase by ~1–3 K for each 1×10²² Am² increase in dipole moment.

Received: 12 Feb 2023 – Discussion started: 15 Feb 2023

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Journal article(s) based on this preprint

12 Jun 2023

Simulated long-term evolution of the thermosphere during the Holocene – Part 2: Circulation and solar tides

Xu Zhou, Xinan Yue, Yihui Cai, Zhipeng Ren, Yong Wei, and Yongxin Pan

Atmos. Chem. Phys., 23, 6383–6393, https://doi.org/10.5194/acp-23-6383-2023,https://doi.org/10.5194/acp-23-6383-2023, 2023

Short summary

Xu Zhou et al.

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-234', Anonymous Referee #1, 22 Feb 2023

This work presents new and very interesting results regarding the paleo-thermosphere, linked to a previous work of the authors (Simulated Long‐Term Evolution of the Ionosphere During the Holocene). The research considering the Earth’s magnetic field of internal origin and the CO2 levels variation along the Holocene is important for long-term trend studies linked to climatic changes in the whole atmosphere, and also for short term analysis since the background thermosphere is key to understanding variabilities at any timescale.
I have only some minor comments to be considered by the authors:
* In Figure 2: Why is it opposite the changes in V between the northern and the southern hemisphere? Maybe I am missing something here.
* Figure 6: Why average between +30 and -30? That is the region enclosing the magentic equator, so there can be different variations in each hemisphere, so they will eventually cancel.
* What about the variation of the magnetic equator (or geomagnetic equator) along the holocene. Because I understand that you are considering an almost dipolar field, but not axial. So the changes in its tilt (and displacement form the center in addition) would contribute to the equator shifts.
Very minor corrections:
* Line 34: I think that in “since the Holocene”, it may should be “since the beginning of the Holocene”, or something like this.
* Line 56: in “The geomagnetic tiled angle ...” I think tiled has a typo error. I think it may be “tilt” or linked to this ?
* Line 111: in “the thermospheric dynamical response..” there are two dots at the end. Delete one.
* Line 118: in “equatorial meridional winds winds” delete one “winds”
* Line 136: About the fluctuations. Why one pair of values have minus-plus (+-) and the other just minus (-)?
* Line 166: “The circulation change in the northern hemisphere is much larger in the southern hemisphere, regardless during March or June.” I do not understand this sentence. Maybe you want to say that the circulation change was larger in the northen than in the southern hemisphere? And what about “regardsless during March or June? You mean that in the two months it is observed this relative difference between north and south?
* Caption of Figure 1: “Thermospheric circulation is illustrated by contours (zonal) and arrays (meridional and vertical)”. What do you mean by “arrays”? Maybe you mean “arrows”?
* Figure 9. Something is wrong with the values in the colorbar of the left figurre. Shouldn’t they be between 1 and -1?

Citation: https://doi.org/10.5194/egusphere-2023-234-RC1
- AC1: 'Reply on RC1', Xu Zhou, 27 Mar 2023
  
  We thank the referee for his/her valuable comments that have helped to improve the quality and clarity of the manuscript. We have tried our best to address all the comments point-to-point as detailed in the following.
  
  * In Figure 2: Why is it opposite the changes in V between the northern and the southern hemisphere? Maybe I am missing something here.
  Response: Thanks for the comment. The reason for the opposite change in circulation in the northern and southern hemispheres during the equinox is that the mean flow becomes more poleward, and we define the positive V as northward. Thus, the change in V is manifested as positive in the northern hemisphere and negative in the southern hemisphere.
  
  * Figure 6: Why average between +30 and -30? That is the region enclosing the magentic equator, so there can be different variations in each hemisphere, so they will eventually cancel.
  Response: Thanks for the comment. We did the average exactly to eliminate the interhemispheric differences, so could focus on the effect of geomagnetic field variations on the low-latitude day-night differences in the mean state.
  
  * What about the variation of the magnetic equator (or geomagnetic equator) along the holocene. Because I understand that you are considering an almost dipolar field, but not axial. So the changes in its tilt (and displacement form the center in addition) would contribute to the equator shifts.
  Response: Thanks for the comment about the variation of magnetic equator. Changes of magnetic equator are an important factor in the ionosphere-thermosphere system indeed. For example, the EIA or ETA structure would shift according to the tilt change at a given longitude. Figure 1 of Cai et al. (2023), which is the companion of this paper, presented the effect of magnetic field on the thermosphere. However, when discussing the changes in thermospheric dynamics at mid- and low-latitudes, we found the effect of dipole change is more dominant.
  
  * Line 34: I think that in “since the Holocene”, it may should be “since the beginning of the Holocene”, or something like this.
  Response: Thanks for the suggestion, and we have revised this sentence like this.
  
  * Line 56: in “The geomagnetic tiled angle ...” I think tiled has a typo error. I think it may be “tilt” or linked to this ?
  Response: Thanks for pointing out the typo, and we have corrected them in the manuscript.
  
  * Line 111: in “the thermospheric dynamical response..” there are two dots at the end. Delete one.
  Response: Thanks for the careful examination, and we have deleted the surplus comma.
  
  * Line 118: in “equatorial meridional winds winds” delete one “winds”
  Response: Thanks for the suggestion. We are sorry for this typo and we have deleted it.
  
  * Line 136: About the fluctuations. Why one pair of values have minus-plus (+-) and the other just minus (-)?
  Response: Thanks for the comment. The minus-plus indicated the V change is different in the northern and southern hemisphere in March, while it is the same during June.
  
  * Line 166: “The circulation change in the northern hemisphere is much larger in the southern hemisphere, regardless during March or June.” I do not understand this sentence. Maybe you want to say that the circulation change was larger in the northen than in the southern hemisphere? And what about “regardsless during March or June? You mean that in the two months it is observed this relative difference between north and south?
  Response: Thanks for the comment. We do intend to express that the circulation change in the northern hemisphere is greater than the southern hemisphere in different seasons. We are sorry for the misleading and revised the sentence as follows:
  “The circulation change shows a larger change in the northern hemisphere than in the southern hemisphere, in both simulations for March and June.”
  
  * Caption of Figure 1: “Thermospheric circulation is illustrated by contours (zonal) and arrays (meridional and vertical)”. What do you mean by “arrays”? Maybe you mean “arrows”?
  Response: Thanks for the careful check, and we have corrected the mistake.
  
  * Figure 9. Something is wrong with the values in the colorbar of the left figurre. Shouldn’t they be between 1 and -1?
  Response: Thanks for the comment. The values in Figure 9 are not the correlation coefficients, but the coefficient estimates for the linear regression. Hence, we have revised the caption to avoid misunderstanding as follows:
  “Coefficient estimates for the linear regression of (a) DW1-T and (b) SW2-T amplitudes on the geomagnetic dipole moment. The grey shaded area indicates where the absolute values of correlation coefficients are less than 0.6.”
  
  Citation: https://doi.org/10.5194/egusphere-2023-234-AC1
RC2:
'Comment on egusphere-2023-234', Anonymous Referee #2, 26 Apr 2023
This is the first paper on modeling circulations and diurnal tides in the thermosphere on time scale of the whole Holocene. It perfectly suits the special issue it was submitted to. Very low levels of geomagnetic and solar activities used in simulations removed/much suppressed perturbing impact of solar and geomagnetic activities on simulated effects of CO2 and secular change of geomagnetic field. Before publication it is necessary to remove/explain some rather minor flaws and improve English. I recommend minor revision.

Comments:

Lines 51-63: I recommend add sentence “The secular changes of geomagnetic field produce regionally both positive and negative changes, therefore in the global average their effect is negligible (Qian et al., 2021).
Qian, L., McInerney, J. M., Solomon, S. S., Liu, H., and Burns, A. G.: Climate changes in the upper atmosphere: Contributions by the changing greenhouse gas concentrations and Earth’s magnetic field from the 1960s to 2010s, J. Geophys. Res. Space Phys., 126(3), e2020JA029067, https://doi.org/10.1029/2020JA029067, 2021.

In Section 2 you describe scenario CR1 but not CR2 (only reference). Please add for comfort of readers a very brief description of scenario CR2.

Lines 235-236: weaker B induces stronger E x B - ? – purely mathematically weaker B should induces stronger E x B.

Section Discussion, flaws: Another potential flaw: According to GAIA simulations by Liu et al. (2021) the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions.
Liu, H., Tao, C., Jin, H., and Abe, T.: Geomagnetic activity effect on CO₂-driven trend in the thermosphere and ionosphere: Ideal model experiments with GAIA. J. Geophys. Res. Space Phys., 126(1), e2020JA028607, https://doi.org/10.1029/2020JA028607, 2021.

Wording and misprints:
Line 42: some is missing in the sentence – it does not make sense

Line 98: change to “interval from ~80,000 to ~1650 yrs. before present”

Line 134: “varied to be much equatorward/poleward” should be “tends to be more/less equatorward”

Line 153: “than that” should be “of that”

Line 166: “larger in” should be “larger than in”

Line 185: This sentence is not understandable.

Line 207: “merely” should be “merely by”

Line 221: “is the molecular” should be “is that the molecular”

Line 243: “diploe” should be “dipole”

Line 244: something is missing, the sentence does not make sense

Line 272: “significantly” should be “significant”

Line 311: sentence is not understandable

Line 312: “was examined to be non-linearly growth” should be “was found to grow non-linearly”

Line 321: “correlated DW1” should be “correlated with the DW1”

Line 488: “contours” should be rather “colors”
Citation: https://doi.org/10.5194/egusphere-2023-234-RC2
- AC2: 'Reply on RC2', Xu Zhou, 01 May 2023
  
  We thank the referee for his/her valuable comments that have helped to improve the quality and clarity of the manuscript. We have tried our best to address all the comments point-to-point as detailed in the following.
  
  Lines 51-63: I recommend add sentence “The secular changes of geomagnetic field produce regionally both positive and negative changes, therefore in the global average their effect is negligible (Qian et al., 2021).
  Qian, L., McInerney, J. M., Solomon, S. S., Liu, H., and Burns, A. G.: Climate changes in the upper atmosphere: Contributions by the changing greenhouse gas concentrations and Earth’s magnetic field from the 1960s to 2010s, J. Geophys. Res. Space Phys., 126(3), e2020JA029067, https://doi.org/10.1029/2020JA029067, 2021.
  Response: Thanks for the suggestion. We have added this sentence and reference in the manuscript.
  
  In Section 2 you describe scenario CR1 but not CR2 (only reference). Please add for comfort of readers a very brief description of scenario CR2.
  Response: Thanks for the comment. We have added the following sentences to describe the CR2 scenario in the manuscript:
  “…The secular variation of geomagnetic field implemented in the CR2, including the dipole moment and the position of magnetic and geomagnetic pole, was illustrated in Figure 1 of Yue et al. (2022), and the readers could refer to Constable et al. (2016) for more detailed information. A general scenario includes: a) the dipole moment fluctuated within 6.1–10.1 (1022AM2), and has continuously decreased since 1700 by ~13%. b) The geomagnetic/magnetic pole located at latitudes larger than 78°/70°, and drifted from the western hemisphere to the eastern hemisphere over the past century…”
  
  Lines 235-236: weaker B induces stronger E x B - ? – purely mathematically weaker B should induces stronger E x B.
  Response: Thanks for the comment. Assuming the E-field unchanged, the inverse relationship is generally valid as the drift velocity is ExB/B². Hence, we revised the manuscript to avoid the misleading as following:
  “…Generally, the smaller strength of the geomagnetic fields would induce stronger equatorial vertical drift (E×B/B²) and thus increase the electron density at the EIA peaks…”
  
  Section Discussion, flaws: Another potential flaw: According to GAIA simulations by Liu et al. (2021) the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions.
  Liu, H., Tao, C., Jin, H., and Abe, T.: Geomagnetic activity effect on CO2-driven trend in the thermosphere and ionosphere: Ideal model experiments with GAIA. J. Geophys. Res. Space Phys., 126(1), e2020JA028607, https://doi.org/10.1029/2020JA028607, 2021.
  Response: Thanks for the comment. We have added some discussion about this point as following:
  “In addition, this paper only considered the geomagnetically quiet condition, while the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions according to GAIA simulations by Liu et al. (2021).”
  
  Wording and misprints:
  Line 42: some is missing in the sentence – it does not make sense
  Line 98: change to “interval from ~80,000 to ~1650 yrs. before present”
  Line 134: “varied to be much equatorward/poleward” should be “tends to be more/less equatorward”
  Line 153: “than that” should be “of that”
  Line 166: “larger in” should be “larger than in”
  Line 185: This sentence is not understandable.
  Line 207: “merely” should be “merely by”
  Line 221: “is the molecular” should be “is that the molecular”
  Line 243: “diploe” should be “dipole”
  Line 244: something is missing, the sentence does not make sense
  Line 272: “significantly” should be “significant”
  Line 311: sentence is not understandable
  Line 312: “was examined to be non-linearly growth” should be “was found to grow non-linearly”
  Line 321: “correlated DW1” should be “correlated with the DW1”
  Line 488: “contours” should be rather “colors”
  Response: Thanks for the careful check. We have corrected the mistakes pointed out by the referee.
  
  Citation: https://doi.org/10.5194/egusphere-2023-234-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-234', Anonymous Referee #1, 22 Feb 2023

This work presents new and very interesting results regarding the paleo-thermosphere, linked to a previous work of the authors (Simulated Long‐Term Evolution of the Ionosphere During the Holocene). The research considering the Earth’s magnetic field of internal origin and the CO2 levels variation along the Holocene is important for long-term trend studies linked to climatic changes in the whole atmosphere, and also for short term analysis since the background thermosphere is key to understanding variabilities at any timescale.
I have only some minor comments to be considered by the authors:
* In Figure 2: Why is it opposite the changes in V between the northern and the southern hemisphere? Maybe I am missing something here.
* Figure 6: Why average between +30 and -30? That is the region enclosing the magentic equator, so there can be different variations in each hemisphere, so they will eventually cancel.
* What about the variation of the magnetic equator (or geomagnetic equator) along the holocene. Because I understand that you are considering an almost dipolar field, but not axial. So the changes in its tilt (and displacement form the center in addition) would contribute to the equator shifts.
Very minor corrections:
* Line 34: I think that in “since the Holocene”, it may should be “since the beginning of the Holocene”, or something like this.
* Line 56: in “The geomagnetic tiled angle ...” I think tiled has a typo error. I think it may be “tilt” or linked to this ?
* Line 111: in “the thermospheric dynamical response..” there are two dots at the end. Delete one.
* Line 118: in “equatorial meridional winds winds” delete one “winds”
* Line 136: About the fluctuations. Why one pair of values have minus-plus (+-) and the other just minus (-)?
* Line 166: “The circulation change in the northern hemisphere is much larger in the southern hemisphere, regardless during March or June.” I do not understand this sentence. Maybe you want to say that the circulation change was larger in the northen than in the southern hemisphere? And what about “regardsless during March or June? You mean that in the two months it is observed this relative difference between north and south?
* Caption of Figure 1: “Thermospheric circulation is illustrated by contours (zonal) and arrays (meridional and vertical)”. What do you mean by “arrays”? Maybe you mean “arrows”?
* Figure 9. Something is wrong with the values in the colorbar of the left figurre. Shouldn’t they be between 1 and -1?

Citation: https://doi.org/10.5194/egusphere-2023-234-RC1
- AC1: 'Reply on RC1', Xu Zhou, 27 Mar 2023
  
  We thank the referee for his/her valuable comments that have helped to improve the quality and clarity of the manuscript. We have tried our best to address all the comments point-to-point as detailed in the following.
  
  * In Figure 2: Why is it opposite the changes in V between the northern and the southern hemisphere? Maybe I am missing something here.
  Response: Thanks for the comment. The reason for the opposite change in circulation in the northern and southern hemispheres during the equinox is that the mean flow becomes more poleward, and we define the positive V as northward. Thus, the change in V is manifested as positive in the northern hemisphere and negative in the southern hemisphere.
  
  * Figure 6: Why average between +30 and -30? That is the region enclosing the magentic equator, so there can be different variations in each hemisphere, so they will eventually cancel.
  Response: Thanks for the comment. We did the average exactly to eliminate the interhemispheric differences, so could focus on the effect of geomagnetic field variations on the low-latitude day-night differences in the mean state.
  
  * What about the variation of the magnetic equator (or geomagnetic equator) along the holocene. Because I understand that you are considering an almost dipolar field, but not axial. So the changes in its tilt (and displacement form the center in addition) would contribute to the equator shifts.
  Response: Thanks for the comment about the variation of magnetic equator. Changes of magnetic equator are an important factor in the ionosphere-thermosphere system indeed. For example, the EIA or ETA structure would shift according to the tilt change at a given longitude. Figure 1 of Cai et al. (2023), which is the companion of this paper, presented the effect of magnetic field on the thermosphere. However, when discussing the changes in thermospheric dynamics at mid- and low-latitudes, we found the effect of dipole change is more dominant.
  
  * Line 34: I think that in “since the Holocene”, it may should be “since the beginning of the Holocene”, or something like this.
  Response: Thanks for the suggestion, and we have revised this sentence like this.
  
  * Line 56: in “The geomagnetic tiled angle ...” I think tiled has a typo error. I think it may be “tilt” or linked to this ?
  Response: Thanks for pointing out the typo, and we have corrected them in the manuscript.
  
  * Line 111: in “the thermospheric dynamical response..” there are two dots at the end. Delete one.
  Response: Thanks for the careful examination, and we have deleted the surplus comma.
  
  * Line 118: in “equatorial meridional winds winds” delete one “winds”
  Response: Thanks for the suggestion. We are sorry for this typo and we have deleted it.
  
  * Line 136: About the fluctuations. Why one pair of values have minus-plus (+-) and the other just minus (-)?
  Response: Thanks for the comment. The minus-plus indicated the V change is different in the northern and southern hemisphere in March, while it is the same during June.
  
  * Line 166: “The circulation change in the northern hemisphere is much larger in the southern hemisphere, regardless during March or June.” I do not understand this sentence. Maybe you want to say that the circulation change was larger in the northen than in the southern hemisphere? And what about “regardsless during March or June? You mean that in the two months it is observed this relative difference between north and south?
  Response: Thanks for the comment. We do intend to express that the circulation change in the northern hemisphere is greater than the southern hemisphere in different seasons. We are sorry for the misleading and revised the sentence as follows:
  “The circulation change shows a larger change in the northern hemisphere than in the southern hemisphere, in both simulations for March and June.”
  
  * Caption of Figure 1: “Thermospheric circulation is illustrated by contours (zonal) and arrays (meridional and vertical)”. What do you mean by “arrays”? Maybe you mean “arrows”?
  Response: Thanks for the careful check, and we have corrected the mistake.
  
  * Figure 9. Something is wrong with the values in the colorbar of the left figurre. Shouldn’t they be between 1 and -1?
  Response: Thanks for the comment. The values in Figure 9 are not the correlation coefficients, but the coefficient estimates for the linear regression. Hence, we have revised the caption to avoid misunderstanding as follows:
  “Coefficient estimates for the linear regression of (a) DW1-T and (b) SW2-T amplitudes on the geomagnetic dipole moment. The grey shaded area indicates where the absolute values of correlation coefficients are less than 0.6.”
  
  Citation: https://doi.org/10.5194/egusphere-2023-234-AC1
RC2:
'Comment on egusphere-2023-234', Anonymous Referee #2, 26 Apr 2023
This is the first paper on modeling circulations and diurnal tides in the thermosphere on time scale of the whole Holocene. It perfectly suits the special issue it was submitted to. Very low levels of geomagnetic and solar activities used in simulations removed/much suppressed perturbing impact of solar and geomagnetic activities on simulated effects of CO2 and secular change of geomagnetic field. Before publication it is necessary to remove/explain some rather minor flaws and improve English. I recommend minor revision.

Comments:

Lines 51-63: I recommend add sentence “The secular changes of geomagnetic field produce regionally both positive and negative changes, therefore in the global average their effect is negligible (Qian et al., 2021).
Qian, L., McInerney, J. M., Solomon, S. S., Liu, H., and Burns, A. G.: Climate changes in the upper atmosphere: Contributions by the changing greenhouse gas concentrations and Earth’s magnetic field from the 1960s to 2010s, J. Geophys. Res. Space Phys., 126(3), e2020JA029067, https://doi.org/10.1029/2020JA029067, 2021.

In Section 2 you describe scenario CR1 but not CR2 (only reference). Please add for comfort of readers a very brief description of scenario CR2.

Lines 235-236: weaker B induces stronger E x B - ? – purely mathematically weaker B should induces stronger E x B.

Section Discussion, flaws: Another potential flaw: According to GAIA simulations by Liu et al. (2021) the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions.
Liu, H., Tao, C., Jin, H., and Abe, T.: Geomagnetic activity effect on CO₂-driven trend in the thermosphere and ionosphere: Ideal model experiments with GAIA. J. Geophys. Res. Space Phys., 126(1), e2020JA028607, https://doi.org/10.1029/2020JA028607, 2021.

Wording and misprints:
Line 42: some is missing in the sentence – it does not make sense

Line 98: change to “interval from ~80,000 to ~1650 yrs. before present”

Line 134: “varied to be much equatorward/poleward” should be “tends to be more/less equatorward”

Line 153: “than that” should be “of that”

Line 166: “larger in” should be “larger than in”

Line 185: This sentence is not understandable.

Line 207: “merely” should be “merely by”

Line 221: “is the molecular” should be “is that the molecular”

Line 243: “diploe” should be “dipole”

Line 244: something is missing, the sentence does not make sense

Line 272: “significantly” should be “significant”

Line 311: sentence is not understandable

Line 312: “was examined to be non-linearly growth” should be “was found to grow non-linearly”

Line 321: “correlated DW1” should be “correlated with the DW1”

Line 488: “contours” should be rather “colors”
Citation: https://doi.org/10.5194/egusphere-2023-234-RC2
- AC2: 'Reply on RC2', Xu Zhou, 01 May 2023
  
  We thank the referee for his/her valuable comments that have helped to improve the quality and clarity of the manuscript. We have tried our best to address all the comments point-to-point as detailed in the following.
  
  Lines 51-63: I recommend add sentence “The secular changes of geomagnetic field produce regionally both positive and negative changes, therefore in the global average their effect is negligible (Qian et al., 2021).
  Qian, L., McInerney, J. M., Solomon, S. S., Liu, H., and Burns, A. G.: Climate changes in the upper atmosphere: Contributions by the changing greenhouse gas concentrations and Earth’s magnetic field from the 1960s to 2010s, J. Geophys. Res. Space Phys., 126(3), e2020JA029067, https://doi.org/10.1029/2020JA029067, 2021.
  Response: Thanks for the suggestion. We have added this sentence and reference in the manuscript.
  
  In Section 2 you describe scenario CR1 but not CR2 (only reference). Please add for comfort of readers a very brief description of scenario CR2.
  Response: Thanks for the comment. We have added the following sentences to describe the CR2 scenario in the manuscript:
  “…The secular variation of geomagnetic field implemented in the CR2, including the dipole moment and the position of magnetic and geomagnetic pole, was illustrated in Figure 1 of Yue et al. (2022), and the readers could refer to Constable et al. (2016) for more detailed information. A general scenario includes: a) the dipole moment fluctuated within 6.1–10.1 (1022AM2), and has continuously decreased since 1700 by ~13%. b) The geomagnetic/magnetic pole located at latitudes larger than 78°/70°, and drifted from the western hemisphere to the eastern hemisphere over the past century…”
  
  Lines 235-236: weaker B induces stronger E x B - ? – purely mathematically weaker B should induces stronger E x B.
  Response: Thanks for the comment. Assuming the E-field unchanged, the inverse relationship is generally valid as the drift velocity is ExB/B². Hence, we revised the manuscript to avoid the misleading as following:
  “…Generally, the smaller strength of the geomagnetic fields would induce stronger equatorial vertical drift (E×B/B²) and thus increase the electron density at the EIA peaks…”
  
  Section Discussion, flaws: Another potential flaw: According to GAIA simulations by Liu et al. (2021) the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions.
  Liu, H., Tao, C., Jin, H., and Abe, T.: Geomagnetic activity effect on CO2-driven trend in the thermosphere and ionosphere: Ideal model experiments with GAIA. J. Geophys. Res. Space Phys., 126(1), e2020JA028607, https://doi.org/10.1029/2020JA028607, 2021.
  Response: Thanks for the comment. We have added some discussion about this point as following:
  “In addition, this paper only considered the geomagnetically quiet condition, while the efficiency of CO2 forcing somewhat differs under low and high geomagnetic activity conditions according to GAIA simulations by Liu et al. (2021).”
  
  Wording and misprints:
  Line 42: some is missing in the sentence – it does not make sense
  Line 98: change to “interval from ~80,000 to ~1650 yrs. before present”
  Line 134: “varied to be much equatorward/poleward” should be “tends to be more/less equatorward”
  Line 153: “than that” should be “of that”
  Line 166: “larger in” should be “larger than in”
  Line 185: This sentence is not understandable.
  Line 207: “merely” should be “merely by”
  Line 221: “is the molecular” should be “is that the molecular”
  Line 243: “diploe” should be “dipole”
  Line 244: something is missing, the sentence does not make sense
  Line 272: “significantly” should be “significant”
  Line 311: sentence is not understandable
  Line 312: “was examined to be non-linearly growth” should be “was found to grow non-linearly”
  Line 321: “correlated DW1” should be “correlated with the DW1”
  Line 488: “contours” should be rather “colors”
  Response: Thanks for the careful check. We have corrected the mistakes pointed out by the referee.
  
  Citation: https://doi.org/10.5194/egusphere-2023-234-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Xu Zhou on behalf of the Authors (01 May 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (09 May 2023) by John Plane

AR by Xu Zhou on behalf of the Authors (12 May 2023)

Journal article(s) based on this preprint

12 Jun 2023

Simulated long-term evolution of the thermosphere during the Holocene – Part 2: Circulation and solar tides

Xu Zhou, Xinan Yue, Yihui Cai, Zhipeng Ren, Yong Wei, and Yongxin Pan

Atmos. Chem. Phys., 23, 6383–6393, https://doi.org/10.5194/acp-23-6383-2023,https://doi.org/10.5194/acp-23-6383-2023, 2023

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Xu Zhou et al.

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Month	HTML	PDF	XML	Total
Feb 2023	97	22	6	125
Mar 2023	53	18	4	75
Apr 2023	38	13	2	53
May 2023	25	7	0	32
Jun 2023	1	2	0	3

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Secular variations in CO₂ concentration and geomagnetic field can affect the dynamics of the upper atmosphere. In this paper, we examine how these two factors influence the dynamics of the upper atmosphere during the Holocene, using two sets of ~12,000-yr control runs by the coupled thermosphere-ionosphere model. The main results show that: 1. increased CO₂ enhances the thermospheric circulation, but non-linearly. 2. Geomagnetic variation induced a significant hemispheric asymmetrical effect.


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