Statistical Study of Geo-Effectiveness of Planar Magnetic Structures Evolved within ICME’s

Round 1

Reviewer 1 Report

The study is devoted to the statistical analysis of planar and non-planar solar wind structures like ICME sheaths and magnetic clouds (МС) and their geo-efficiency.  Extensive statistical material is considered, including 420 ICME events observed from 1998 to 2017.  The authors have found that intense and extreme geomagnetic storms are observed more often during planar ICMEs compared to non-planar ones, and they conclude that planar structures are more geo-efficient. The topic of the study is interesting and actual, especially for the problem of space weather prediction.  

The paper is well written, the pictures and tables are understandable, the results are clearly described. But there are several general points that need to be resolved before publication:

1.     The critical point is the selection of the objects under consideration. It is not clear why the authors consider sheaths and magnetic clouds as sub-structures of the ICME (see page 6 line 191). This is not a completely correct statement. MCs are subtype of the ICMEs with higher and more regular magnetic field than other ICMEs (ejecta) see for example Burlaga 1991. On the other side, the Sheath is the compression region before ICME’s, both before MC and Ejecta. So, it would be more correct to consider separately two types of ICME (MC and Ejecta) and two types of Sheaths (Sheaths before MC and before Ejecta), for planar and non-planar events respectively.  

2.     Some papers discuss that Sheath's are more geoeffective than ICME's , see for example (Huttunen  2004, Guo et al., 2011, Yermolaev et al., 2012). It would be interesting to define which factor is more important for geoeffectiveness – the Sheath regions before ICMEs or the planarity of the ICME?

3.      Page 2 lines 52-54: The authors  claim "The in-situ observations of the ICME depict three notable structures, i.e. forward propagating shock, compressed and turbulent sheath, region, and the orderly magnetized flux rope connected to the Sun" . It's not entirely correct statement, while Sheath regions can be observed even in the absence of interplanetary shock (IS), and this type of drivers «sheath without IS» can generate at least 10% rather strong magnetic storms see for example (Yermolaev et al., 2020). It would be useful to take into account this moment and to consider separately the Sheath without IS.

4.     Little attention is paid to the comparison of geoeffectiveness for different solar wind types   see for example Tsurutani et al;1997,   Gonzalez et al., 1999, Yermolaev 2021.  It is necessary to add such discussion to the  sections "introduction" and "Discussion".

5.     The difference between planar and non-planar events discussed by authors is poorly visible for some histograms at Figure 3.  To prove the statistical significance of the results, it is necessary to add standard deviations and errors of the mean values for each histogram.

6.     The results presented in tables 1 and 3 should also be supplemented by calculated errors for each mean values.

There are also a few minor remarks:

 1.     Page 2 line 46 – It ‘s not clear why is it used the question mark « 17?»

2.     Page 3 line 111 " viz ;"  - possibly it should be " viz. "

3.     A link to Fig. 2 is given first then to Fig. 1, the figures should be swapped, or to give  a link to Figure 1 at the beginning of the section "Data and Results".

4.     Page 3:  it's written that  planar sheath events are labeled by light blue color (the legend of the figure 1), however, this color is not present at the figure, presumably these phenomena are indicated in gray color.  This moment needs to be clarified in the legend of the figure.

5.     Page 4: The content of table 1 completely duplicates the inscriptions at the fig. 3. At the same time Table 1 is not mentioned anywhere in the text. The table should  be removed from the text (or remove the inscriptions from the Figure 3), if the table will remain - add a description of the table into the text.

6.     Page 4: mean values in table 1 are shown with 3-4 decimal places - it makes no sense, it is unlikely that the error of the mean is so small. The number of decimal places need to match the error of the mean values. The same situation is for table 3.

7.     Page 4 lines  126-129:  the term " left-skewed" is not clear enough, it would be better to write something like  "the distributions have an asymmetrical tail toward lower SYM-H index values".

Burlaga, L.F.E. . Magnetic Clouds. In: Schwenn, R., Marsch, E. (eds) Physics of the Inner Heliosphere II. Physics and Chemistry in Space,  1991, vol 21. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-75364-0_1

Huttunen, K.E.J.; Koskinen, H.E.J. Importance of post-shock streams and sheath region as drivers of intense magnetospheric storms and high-latitude activity. Ann. Geophys. 2004, 22, 1729–1738.

Guo, J.; Feng, X.; Emery, B.A.; Zhang, J.; Xiang, C.; Shen, F.; Song, W. Energy transfer during intense geomagnetic storms driven by interplanetary coronal mass ejections and their sheath regions. J. Geophys. Res. 2011, 116, A05106.

Yermolaev, Y.I.; Nikolaeva, N.S.; Lodkina, I.G.; Yermolaev, M.Y. Geoeffectiveness and efficiency of CIR, sheath, and ICME in generation of magnetic storms. J. Geophys. Res. 2012, 117, A00L007.

Yermolaev, Y.I.; Lodkina, I.G.; Yermolaev, M.Y.; Riazantseva, M.O.; Khokhlachev, A.A. Some Problems of Identifying Types of Large-Scale SolarWind and Their Role in the Physics of the Magnetosphere: 4. The “Lost Driver”. Cosm. Res. 2020, 58, 492–500.

Tsurutani, B.T.; Gonzalez, W.D. The interplanetary Causes of Magnetic Storms: A Review. In Magnetic Storms; Mon, S., Tsurutani, B.T., Gonzalez, W.D., Kamide, Y., Eds.; American Geophysical Union Press: Washington, DC, USA, 1997; Volume 98, p. 77.

Gonzalez,W.D.; Tsurutani, B.T.; Clua de Gonzalez, A.L. Interplanetary origion of geomagnetic storms. Space Sci. Rev. 1999, 88, 529–562.

Yermolaev, Y.I.; Lodkina, I.G.; Dremukhina, L.A.; Yermolaev, M.Y.; Khokhlachev, A.A., What Solar–Terrestrial Link Researchers Should Know about Interplanetary Drivers. Universe 2021, 7, 138. https://doi.org/10.3390/ universe7050138

Author Response

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Reviewer 2 Report

The paper provides a statistical analysis of the strength of geomagnetic storms in a large sample of ICMEs, including magnetic clouds. The key factors for a geomagnetic storm are large values of interplanetary Bz for a long period together with a dusk-ward convection electric field.

The author’s aim is to identify the key factors contributing to the geoeffectiveness of the storms. Knowing that the IMF orientation strongly influences geomagnetic activity, they suspect that the structure of ICME sheaths (and MCs) could play a significant role. In particular, on a data set of 420 storms, they compare the plasma characteristics of all events with a subset of two-dimensional pancake shaped “Planar Magnetic Structures (PMS)”. These are what the ICME flux ropes can transform into (due to compression), as suggested by the same authors earlier. The authors also proposed that in PMS ICME sheaths, the plasma parameters and N/S magnetic fields are much stronger than those of non-planar ones suggesting that PMS can be the cause of stronger storms.

After a detailed summary of earlier findings, the second chapter presents the database and summarizes the statistical results. To characterize the strength of storms, the DST geomagnetic storm index and the SYM-H index are taken from the OMNI database. The in situ plasma parameters were obtained from the ACE s/c measurements. The determination of the SYM-H high and low index values are presented in Figure 2. For the selection criteria of PMSs the method of Nakagawa et al (1989) was adopted. The total of 420 ICMEs was split into 4 categories: 3 containing planar structures divided according to which part of an ICME transforms into planar structures, and non-planar ICMEs.  The non-planar structures represent about 50% of the whole set of events. Table 1 summarizes the parameters of the distribution of the minima (during the initial phase) and maxima (in the main phase) of SYM-H values according to the four categories. It could be useful to add the minimum and maximum values of SYM-H High and Low as well. Figure 3 compares the distributions themselves, indicating that the SYM-H maxima follow a quasi Gaussian distribution. For the minima, it is asymmetric for both non-planar and planar ones of all ICMEs. What could be explained is the reason for this asymmetry. One can argue that SYM-H low cannot be positive (larger than the interplanetary value (no storm otherwise) and the right side of the SYM-H low distribution contains small storms. Table 3 is a comparison of plasma and magnetic field data for planar and non-planar structures, indicating more disturbed higher plasma values for the latter. The Discussion chapter enumerates a couple of new findings related to geomagnetic storms. One new reference about extreme events might be added (Bergin et al. 2023 https://doi.org/10.1029/2022SW003304).

The main conclusions of the paper, supported by the statistical analysis presented, are, on one hand, that planar structures form due to compression. On the other hand, all parts of ICMEs that transform into planar magnetic structures give rise to stronger geomagnetic storms and enhanced plasma parameters. The higher geomagnetic activity found for planar structures due to elevated magnetopause current and ring current is a new result and worth investigating in a wider context.

Minor – mainly grammatical - corrections

line 3 magnetic clouds

9 molded

10 that planar

32 at the initial phase

39 this causes

63 oriented

91 ICME was due

98 catalog

101 characteristics

110 disturbances

111 viz.,

143 left occurrence probability

148 resulted in

191 molded

223 that converts

225 causes

231 (delete “those”)

236 may be required

the language of the manuscript is OK

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

see in attach file

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors  took into account all the comments, and the quality of the article has become much better. So the paper can be published in its current form.