Polar Middle Atmospheric Responses to Medium Energy Electron (MEE) Precipitation Using Numerical Model Simulations

Round 1

Reviewer 1 Report

Reviewer’s comments to the paper by Lee et al. “Polar middle atmospheric responses…”

It is widely known that there is a cycle of photochemical processes with participations of molecules of the NOx and HOx families which lead to a destruction of ozone. The cycle is governed mainly by the solar UV radiation. However, the latter becomes absorbed, the stronger the deeper we descend into the middle atmosphere. In these conditions, the role of particle-generated effects in formation of both families and thus in the ozone destruction increases.

The paper under review present an investigation of the chemical effects of the medium-to-high energy electrons (MEE) precipitation in the polar atmosphere. The authors consider also the associated dynamical changes, which may lead to the regional climate changes.

The study is based on a model simulation with the help of the Specific Dynamics (SD) version of the Whole Atmosphere Community Climate Model (WACCM). The latter is in my opinion the best available model of the middle and upper atmosphere frequently used to analyze changes in the atmosphere caused by various factors, especially by long-term trends of the anthropogenic origin. The paper is aimed to investigation of the responses of the middle atmosphere to MEE precipitation in the polar region during a period of 2005 to 2013. The effects of solar proton events (SPE) in changing the middle atmosphere chemistry are also considered.

The numerical simulation of the electron precipitation effects in the middle atmosphere is performed by implementing the MEE ionization rate into the WACCM model. The MEE ionization rate is calculated from the MEE precipitation model that is a part of solar forcing recommendation for the sixth Coupled Model Intercomparison Project (CMIP6)

The simulation results demonstrate that there are substantial changes in all considered chemical compounds (NO, H₂O, O₃). These changes are distinctly illustrated in numerous figures and described in the text. For example, the effects of the increase in NO are visually seen in Fig. 2. The maximal effect is seen at heights of 80-90 km, but some influence is seen down to 30 km. An astonishing difference is seen if the Northern and Southern hemispheres are compared.

The computation results show also that the MEE intrusions also cause substantial changes in the dynamical and temperature regime. These changes also are distinctly illustrated by the figures and discussed in the text.

I consider the paper as a very interesting and important contribution into studies of the middle atmosphere photochemistry and physics and recommend publication of the paper with a minor revision.

My comment to the essence of the paper is as follows. As far as I remember, no clustered-ion chemistry at heights of the ionospheric D region is considered in the Model of Ozone and Related Chemical Tracers (MOZART) included into the WACCM model. However, at heights of 60-80 km, both molecules NO and H₂O participate in transformation of “normal” ions into clustered ions. The latter ions have a very high dissociative recombination coefficient and so rapidly recombine. The process is intensified if the ionization rate increases, which is the case during electron precipitations. I wander if this effect is taken into account in the scheme of photochemical transformations used in the paper under review to reveal the obtained effects.

My second comment is purely technical. The captions to some figures are quite unusual (Fig. 1, Fig. 7 and others). These captions look as some instructions to the publishers but not as explanations to the pictures aimed to help readers. Fortunately, the content of the figures is understandable from the text, but the captions should be corrected. Also: the gray contours are poorly seen in Figs. 4 and 5.

Author Response

Please see the attached file for the responses to reviewer's comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

See attached file. 

Comments for author File: Comments.pdf

Author Response

Please see the attached file for the responses to reviewer's comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

This study uses the SD-WACCM model to simulate the atmospheric response to medium energy electron precipitation during the time period of 2005-2013. Beside the precipitation-induced enhancement of NOx and HOx and loss of O3, the study investigates the resulting effects on the atmospheric temperature and meridional circulation. This study is interesting, straightforward, and easy to follow. I have no problem with this investigation, and would recommend the publication after the concerns outlined below are addressed.

Major concerns:

While nice work has been done in summarizing what has been learned from previous studies, I found two relevant studies (with their references listed below) were not introduced. One is Pettit et al [2019], who also applied the SD-WACCM to quantify the atmospheric impact from >30 keV MEEs. The other is Fang et al. [2007], who examined the atmospheric impact from precipitating medium-energy (>30 keV) protons. Although solar energetic protons have been included in the current numerical work using prescribed particle-impact ionization, the medium-energy proton precipitation from the radiation belt/ring current is neglected. Because proton precipitation from the inner magnetosphere constitutes an ubiquitous source in comparison with the sporadic nature of SPEs, it would be interesting to take into account these medium-energy protons, particularly on a large time scale as in this study.

Pettit, J. M., et al. (2019). Atmospheric effects of >30‐keV energetic electron precipitation in the southern hemisphere winter during 2003. Journal of Geophysical Research: Space Physics, 124, 8138– 8153. https://doi.org/10.1029/2019JA026868

Fang, X., et al. (2007), Global 30–240 keV proton precipitation in the 17–18 April 2002 geomagnetic storms: 3. Impact on the ionosphere and thermosphere, J. Geophys. Res., 112, A07310, doi:10.1029/2006JA012144.

 

Other comments:

1. Title, add “precipitation” after “MEE”
2. Line 23, “medium-to-high energy electrons” (that is, add “s” at the end)
3. Line 24, “MEEs”
4. Line 25, change “Results” to “Our results”
5. Line 28, insert “the temperature” after “but decreases”
6. Line 29, remove “However”
7. Line 30, and throughout the paper, remove “seem to” and “appear to”
8. Line 40, remove “however, the”
9. Line 44, remove “persistently”
10. Lines 52 and 54, two seemingly contradictory energy ranges (30-1000 keV vs 1-4 MeV) were provided when talking about MEEs.
11. Line 61, “70-80 km altitudes” (that is, add “s” to “altitude”)
12. Line 77, change “to show the average” to “and suggested an average”
13. Line 79, I don’t understand how the impact from the combined SPEs, auroral electrons, and MEEs could “implied the importance of MEE”. Something is missing here.
14. Line 80, change “chemical changes just mentioned” to “aforementioned chemical changes”
15. Line 85, change “essential” to “important”
16. Line 103, change “solar proton events (SPE)” to “SPEs”, as the abbreviation has already been introduced.
17. Line 106, by “pre-computed atmospheric ionization rates”, is it implied that in the SD-WACCM run, the model-calculated atmospheric profiles were not used for the SPE ionization calculation? In other words, there is inconsistence here.
18. The figure captions are missing for Figures 1, 7, 8, 9, 10.
19. Figure 1, panels (b) and (c), at what altitudes are these ionization rates obtained?
20. Line 121, change “for a given” to “for any given”
21. Line 124, briefly explain why the time period of 2005-2013 is selected. Why not run a longer time interval to cover at least a solar cycle?
22. Line 126, the Ap index is for the description of geomagnetic activity, not necessarily related with SPEs.
23. Line 129, add reference(s) after the introduction of the WACCM model.
24. Line 141, “wired”?
25. Line 142, remove “is may”
26. Line 143, remove “is” after “SD-WACCM”
27. Line 161, I am confused at the sentence of “the energy of the SPEs exceeds 10 MeV in the geosynchronous orbit”. Is this about the selection criterion of interesting SPEs?
28. Line 166, change “how different the effect” to “different effects”, and remove “are” in the next line.
29. Figure 2. A SPE is marked during the year of 2010 in Figure 2, which looks inconsistent with Figure 1c. I guess it is because the 2010 SPE was not strong enough to cause significant ionization at the specific altitude in Figure 1c. It may be helpful to mark the SPEs in Figure 1c, too.
30. Figure 2, “white short lines” are not legible.
31. Figure 3, why is 7-day running averaging applied in Figure 3, but 10-day running averaging in Figure 2?
32. Figure 4, the areas with the 95% confidence level occupy only a very small fraction of the total areas. Does it mean that we should not trust any results outside of these areas? What is the confidence level outside of these 95% areas?
33. Line 212, insert “with” before “NOx”
34. Line 218, change “HOx” to “NOx”
35. Line 230, change “is increased” to “increases”, and remove “by” before “1 ppbv”.
36. Line 237, change “pole” to “polar region”
37. Line 247, change “governed” to “guided”?
38. Line 260, “Local Thermodynamic Equilibrium” (that is, remove “al” at the end of the middle word)
39. Line 286, I don’t see any gray contours.

Author Response

Please see the attached file for the responses to reviewer's comments.

Author Response File: Author Response.pdf