Analysis of Deformation and Erosion during CME Evolution
Round 1
Reviewer 1 Report
Analysis of deformation and erosion during CME evolution
Skralan Hosteaux, Emmanuel Chané and Stefaan Poedts
In this manuscript, the authors show numerical simulations on normal and inverse CMEs, and analyze the forces acting on CMEs and the role of magnetic reconnection in the evolution of CMEs. In my opinion, the manuscript is written with clear logic, and contains very detailed analyses and some interesting results. Here I have some comments and suggestions for the authors’ consideration.
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Major:
[1] Does the CME erupt immediately after inserting a flux rope in the solar wind background? If so, then the initial state is not quasi-equilibrium at 2 Rs. Will it influence the analysis of CMEs (e.g., forces) during their initial propagation? Or is the simulation in this condition self-consistent?
[2] Refer to the velocity distribution in Figure 1, the CME has the maximum velocity around its center and minimum velocity around the edge. How does the velocity distribution evolve with the CME propagation? I guess it may keep the maximum around the center based on the results shown in the manuscript. However, such a velocity distribution is not consistent with that for an expanding CME.
[3] All the simulated results show that the rear edge of the CME seems to be ‘anchored’ in the lower corona. However, the simulation is 2.5D and the CME in the simulation domain may refer to the CME cross-section in that plane. Maybe the author could discuss more about how this CME shape is related to the real observations (or the 3D flux rope model), and how the shape (velocity distribution) is related to the CME deformation.
[4] Combining point 3, the simulated CME have a very large length (from its rear to front), compared to the length of magnetic clouds in real observations.
[5] Could the authors discuss more about the thermal and magnetic forces on the CMEs? It is generally accepted that magnetic force acts as the dominant role in the CME initial evolution; but the simulations find that the pressure gradient is dominant.
[6] The authors use ideal MHD simulation (based on Eq. 2), and thus magnetic reconnection rate depends on numerical resistivity. Does it influence the numerically reconnected flux? For example, the approximately same amount of magnetic field lines would be reconnected as the CME propagate along the same path length by numerical reconnection, and thus it has no meaning to analyze the relationship between the reconnection/erosion with solar wind density and CME velocity.
[7] How about the forces (thermal and magnetic) inside ICMEs? Based on the figures it is difficult to make a distinguishment because they are too small.
[8] Maybe analyzing the total force acting on the whole ICME (or from the rear crossing the center to the front) would be better for discussing the deceleration of ICMEs.
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Minor:
[9] Line 78: why the speed of ICME does not influence the shock stand-off distance? The stand-off distance is inversely proportional to the square of the upstream Mach number.
[10] Line 88: “only the normal CMEs had a strong negative Bz” --- I guess the direction of Bz for a normal or an inverse CME depends on the polarity of the corona magnetic field.
[11] Line 97: it may be worth having few words describing the meaning of 2.5D.
[12] Line 97: the simulation is in the meridional plane?
[13] Eq. (1): may be better to introduce the parameters.
[14] Line 139: right-hand side ---> right-hand side (RHS).
[15] Line 147: “the tension force is not strong enough” ---> does the tension force depend on the magnetic flux function? If so, then the tension force could be large by setting a large flux function value.
[16] Figure 2: the labels are too small.
[17] Line 192: It shall be Figure 4 and 5?
[18] Figure 6: maybe increase the symbol size.
[19] Figure 10: why there is a sharp decline at 50 Rs for both the normal and inverse CMEs? Numerical effect?
[20] Line 280 to 282: a little bit confusing because the magnetic polarities do not change before and after 18 hours.
[21] Section 2.2.2: maybe state more clearly that the magnetic flux in this manuscript is the ‘poloidal’ magnetic flux.
[22] Line 315: it may be better to describe more about the central arcade.
[23] Line 326: “The one exception is the medium velocity CME in a medium density wind”. Could the authors talk a little bit more about this?
[24] Figure 8: as mentioned by the authors that the CME mass is much larger than the mass estimated in observations, then the authors may would like to discuss more about how the large CME mass influences on the CME propagation. For example, if considering the acceleration/deceleration of a CME in the interplanetary space is mainly controlled by the solar wind drag force, then such a heavy CME would not experience strong acceleration or deceleration due to the drag. Furthermore, how to determine the CME length perpendicular to the simulation domain when calculating the CME mass.
[25] Section 2.3: how well the conservation law (e.g., mass) could keep with ARM (ARM needs interpolation?).
Comments for author File: 
Comments.pdf
Author Response
See PDF in annex.
Author Response File: Author Response.pdf
Reviewer 2 Report
This article presents an analysis of 2.5D MHD simulations of idealised CMEs propagating from low in the solar atmosphere, out to Earth-like distances. The authors investigate how the balance of forces on a CME changes as a function of CME scenario, and ambient solar wind scenario. The authors use these simulations to draw conclusions on how the different magnetic and mass density structures affect a CMEs kinematics, as well as how the total mass and magnetic flux of a CME evolves during its propagation.
I am not expert in the 2.5D MHD simulation, but I am familiar with numerical modelling and specifically the numerical modelling of CMES. To the best of my knowledge, I see no significant scientific issues with the construction and analysis of the simulations, or the authors authors discussion and conclusion of these works. I think the article is generally clearly written and the conlusions are supported by the presented simulation results.
My only significant criticism of the article is in the formatting of some of the figures, particularly figures 2, 3, 4, and 5. All of these figures are a little fuzzy, presumeably as they are images rather than vector graphics? But, there are two important issues regarding the choice of colormaps in these figures.
Firstly, these colormaps are not perceptually uniform, which distorts our ability to interpret the figures correctly. Secondly, they contain both red and green, which is a needless challange to readers with color vision deficiency - likely to be around 10% of your readers. Crameri et al. 2020 discusses these issues, and how they can be rectified (https://doi.org/10.1038/s41467-020-19160-7). Please consider the content of this reference and consider making changes to the figures.
My only other minor comment is that it might be of interest to discuss how your magnetic flux erosion estimates compare with estimates derived from observations of magnetic clouds - e.g. Ruffenach et al. 2012 (https://doi.org/10.1029/2012JA017624) or there are a range of other references available. If you do so, it might be interesting to see if this is also consistent with the mass erosion estimates that you do compare with observations.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The manuscript was significantly improved. I would love to support its publication in Geosciences.
Reviewer 2 Report
I'm surprised that, after considering the reference that describes why their chosen colormaps are inappropriate, that the authors have decided to continue using them.
Their statement that "the choice of the colour bar depends also on the gradients. We think we would lose information if we change the colour bars." precisely highlights the problem. That "information" that you expect you would loose is not really there - it is an artefact of a poorly constructed colormap that is not perceptually uniform.
Fixing this problem would have been a minor issue, but I consider failing to engage with it a major issue. Refusing to change colormaps that misrepresent your data is a poor decision that makes your science harder for interested readers to interpret.
However, MDPI have no policy or guidance on this, and so I do not feel it would be appropriate for me to request further revisions. I suggest that it should be an editorial decision about whether to allow these data to be presented in this way.
