Longitudinal Evolution of Storm-Enhanced Densities: A Case Study
Round 1
Reviewer 1 Report
Comments on the manuscript
‘Longitudinal Evolution of the Storm Enhanced Density: A case study’
Submitted to
Remote Sensing
By
Bo Li, Huijun Le, Wenbo Li, Yiding Chen, Libo Liu
General Comments:
This work shows interesting results about the SED during a magnetic storm. However, I think the lack of physical discussion. Therefore, this paper needs a major revision before publication. I encourage the authors to answer these questions to clarify the ideas of this study.
Comments:
1. The abstract needs to be clearer. Also, define the SED and other abbreviations.
2. Lines 34-36: Please, rewrite this phrase to a better understood.
3. Lines 44-45: What the authors mean by “One reason for this phenomenon is the limited global coverage of GPS receivers in the middle and high latitudes”. I believe that the GPS receivers cover very well the middle latitudes.
4. Lines 75-76: Many works included the enhancement of the TEC during magnetic storms over low latitudes and equatorial sites. I think the authors need to rewrite this phrase and include some other works, such as:
• Venkatesh et al. (2017), Electrodynamic disturbances in the Brazilian equatorial and low-latitude ionosphere on St. Patrick’s Day storm of 17 March 2015, J. Geophys. Res. Space Physics, 122, 4553–4570, doi:10.1002/2017JA024009.
• Fagundes et al. (2016), Positive and negative GPS-TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian sector, J. Geophys. Res. Space Physics, 121, 5613–5625, doi:10.1002/2015JA022214.
5. Other works are important to have in the Introduction:
• Förster, M., and N. Jakowski (2000), Geomagnetic storm effects on the topside ionosphere and plasmasphere: A compact tutorial and new results, Surv. Geophys., 21, 47–87, doi:10.1023/A:1006775125220.
• Fuller-Rowell, T. J., M. V. Codrescu, R. J. Moffett, and S. Quegan (1994), Response of the thermosphere and ionosphere to geomagnetic storms, J. Geophys. Res., 99, 3893–3914, doi:10.1029/93JA02015.
• Fuller-Rowell, T. J., M. V. Codrescu, H. Rishbeth, R. J. Moffett, and S. Quegan (1996), On the seasonal response of the thermosphere and ionosphere to geomagnetic storms, J. Geophys. Res., 101, 2343–2353, doi:10.1029/95JA01614.
6. Lines 109- 110: In relation to Figure 1: The authors refer to the black curves or black lines. Please, clarify Figure 1.
7. Figure 2: Describe this figure better. What is the structure? CME or HSS? The phrase: “It means the energy of solar wind is steady and persistent” is incomplete, in my opinion.
8. Discussion: I think that the prompt penetration electric field can have some influence on the SED. It is important to have a physical discussion about the disturbed electric field's role.
9. Line 218-219: These hours are related to the magnetic storm's recovery phase. I miss the physical discussion about this behavior.
10. Lines 223-224. The reversal enhancement peak (PRE) occurs very clearly in equatorial regions. However, we observe in some stations over low and middle latitudes. Is there an influence in the SED before the nighttime
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper studies the longitudinal evolution of SED and explains the physical process for the structure. At the same, they found the two-SED structure during the storm. It is written clearly and presents informative figures. The abstract adequately presents the obtained in the paper results. As a consequence, I recommend its publication almost in its present form. I have only several very minor comments/questions that need to be clarified.
Comments：
1. Line 127：A space is necessary behind AE.
2. SED longitude variations in this paper have any differences with neglecting results reported by Coster’s results?
3. SED has been nearly recovered in Figures c1 and d1, whereas the Bz, AE, and SYM-H were still large. Whether the results represent that the effects of geomagnetically disturbed duration are minor during the storm recovery phase?
4. The two-SED structure is interesting. The reason for the occurrence of second SED?
Author Response
Please see the attachment.
Author Response File: 
Author Response.doc
Reviewer 3 Report
The authors investigated the dynamic longitudinal evolution of the Storm Enhanced Density (SED) from the Europe sector to the North American sector, for the first time, during the July 15, 2012 storm, its main phase lasted nearly 30 hours, maintaining the stable interplanetary magnetic field and solar wind input conditions. First, they plotted a time series of polar maps of the GPS TEC and corresponding SED plume boundaries of four UT points defined by a value of 13 TECU according to the TEC's spatial distribution in the northern hemisphere with local noon on the top. Next, in order to check the examination of the longitude dependence of the TEC magnitude of the plume, they plotted universal time variations of the parameters of the maximum TEC value bin (mTECb) in a SED area on July 15, 2012. And then in the section “Discussion” they used the regional eastward auroral electrojets indices from SuperMAG to study the relationship between the eastward electric field and the SED motion, and described an important role of electric field in the longitude dependence of the SED structure. Also the authors found, for the first time, ground-based observations of the double-SEDs structure lasted for about 1 hour. Obtained results of SED’s study during the July 15, 2012 storm based on above-mentioned plots with its detailed descriptions are new findings of the manuscript.
There does remain a level of uncertainty that needs to be addressed, however.
Thus, it is recommended the manuscript to be accepted by Remote Sensing after major revision.
Comments
Major:
(i) What motive is chosen by the authors for selection of 13 TECU value to determine SED plume boundaries?
Also, on the opinion of the reviewer, a determination of SED plume boundaries as “poleward and equatorward boundaries” in Figure 3 is confusing. Corresponding SED plume boundaries for first three UT points in the northern hemisphere are stretched to the pole than ones are aligned on longitude.
(ii) Please explain in text, how a values of CPCP obtained or calculated?
(iii) Double-SEDs structure observed by GPS TEC data during the July 15, 2012 storm is new result. In this case, the reviewer would like to know whether validations of second SED (or plume) have been made using satellite and incoherent scatter radar data?
By the way, Spasojevic et al. [Spasojevic et al., J. Geophys. Res. 2003, doi: 10.1029/2003JA009987] have been explained second SED as following “The plasmaspheric plume has wrapped around the main plasmapause and second plume has formed as a result of the rotation of the shoulder into the dusk sector.” (see their Figure 16).
(iv) Please make Citations and References according to Instructions for Authors.
https://www.mdpi.com/journal/remotesensing/instructions
For the convenience of readers, please indicate the DOI number for references.
(v) English in the manuscript needs improving. It would be better, if the authors consulted an English speaker.
In particular, please check following terms.
on North American sectors (see L.14) & on the North American sector (see L.75);
longitudinal evolution (see L.14) & the longitude evolution (see L.17-18);
Please correct the following term.
movement --> motion
Line 67: the movements
Line 237: the SED movement
Line 241: the SED movement
Line 276: SED movement
Line 277: the movement of the SED
Minor
Line 74: under magnetically disturbed conditions with Kp=6.
Please add the term “geomagnetic index” for Kp.
/Figure 2 caption/
Line 122: Kp index; --> Kp index (vertical dashed red line with dot);
Line 123: (f) the cross polar cap potential --> (f) the cross polar cap potential (CPCP)
Line 123: The vertical red gives the UT --> The vertical red line gives the UT
Line 127: CPCP (panel f) --> the cross polar cap potential, CPCP (panel f)
Line 148: we can get --> We can get
Line 150: (a1 panel), --> (panel a1),
Line 160: In c2 and d2 panels, --> In panels c2 and d2,
Line 252: in Figure 5, --> in Figure 6,
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Line 45-47. “Another reason is the longitudinal dependence of the SED occurrence rate due to the inconsistency between the geographic and the geomagnetic axes.” – Please explain how this reason impacts the SED structure observation and investigation ?
Line 89. OMNI – please, decode abbreviation.
Line 90. SuperMAG - please, decode abbreviation.
Figure 1. GPS TEC map in the Northern Hemisphere is difficult to read. Description of Figures 1-6 are given 2 times – on the top of Figure and below. Please, do according the template requirements.
In Figure 1 description is used MLAT/MLT (Line 96, 106), in text of article used MLT/MLAT Line 104)., magnetic latitude (M-Lat) and magnetic local time (M-LT) (Line 116). Please, unify.
Figure 2(d). Mistake - Kp index is not measured in nT units.
Line 146 GPS TEC – it would be preferable to give definition: what do you mean GPS TEC ?
Line 167. “Figure 4. Universal time variations of the parameters of the maximum TEC value bin (mTECb) in a SED area on July 15, 2012.” Are there UT variations or parameter variations ???
Line 191. SAPS - please decode abbreviation.
Line 213. M-Lat variation or TECb variation in dependence of M-Lat ???
Line 248. In Figure 6 is shown SED 1, but SED 2 is not shown.
11 sources [10, 12, 13, 14, 22, 25, 26, 27, 28, 29, 32] are not mentioned in the article from the list of 38 references.
Author Response
Please see the attachment.
Author Response File: Author Response.doc
Round 2
Reviewer 3 Report
The authors investigated the dynamic longitudinal evolution of the Storm Enhanced Density (SED) from the European sector to the Northern American sector, for the first time, during the July 15, 2012 storm, its main phase lasted nearly 30 hours, maintaining the stable interplanetary magnetic field and solar wind input conditions. First, they plotted a time series of polar maps of the GPS TEC and corresponding SED plume boundaries of four UT points defined by a value of 13 TECU according to the TEC's spatial distribution in the northern hemisphere with local noon on the top. Next, in order to check the examination of the longitude dependence of the TEC magnitude of the plume, they plotted universal time variations of the parameters of the maximum TEC value bin (mTECb) in a SED area on July 15, 2012. And then in the section “Discussion” they used plasma data from Millstone Hill incoherent scatter radar (MHISR) and the regional eastward auroral electrojets indices from SuperMAG to study the relationship between the SED motion and the eastward electric field. Also the authors found, for the first time, ground-based observations of the double-SEDs structure lasted for about 1 hour. Obtained results of SED’s study during the July 15, 2012 storm based on above-mentioned plots with its detailed descriptions are new findings of the manuscript.
I think this variant of the manuscript properly takes into account my previous comments and can be published in Remote Sensing.
Comments for author File: Comments.pdf
