the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Sep 2022
Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments
Abstract. Scintillations of transionospheric satellite signals during geomagnetic storms can severely threaten navigation accuracy and the integrity of space assets. We analyze vertical Total Electron Content (vTEC) variations from the Global Navigation Satellite System (GNSS) at different latitudes around the world during the geomagnetic storms of June 2015 and August 2018. The resulting ionospheric perturbations at the low-and mid-latitudes are investigated in terms of the prompt penetration electric field (PPEF), the equatorial electrojet (EEJ), and the magnetic H component from INTERMAGNET stations near the equator. East and South-East Asia, Russia, and Oceania exhibited positive vTEC disturbances, while South American stations showed negative vTEC disturbances during both storms. We also analyzed the vTEC from the Swarm satellites and found similar results to the GNSS retrieved vTEC during different phases of both geomagnetic storms. Moreover, we observed that ionospheric plasma tended to increase rapidly during the afternoon in the main phase of the storms. At nighttime, the ionosphere depicted an opposite behavior under similar conditions. The equatorial ionization anomaly (EIA) crest expansion to mid and high latitudes is driven by PPEF during daytime at the main and recovery phases of the storms. The magnetic H component exhibits a longitudinal behavior along with the EEJ enhancement near the magnetic equator.
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RC1: 'Comment on angeo-2022-18', Anonymous Referee #1, 19 Oct 2022
Comments to “Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments” by Rasim Shahzad et al.
Ionospheric responses to magnetic storms have been widely investigated due to the remarkable influences of storms on the space environment. In this paper the authors used multiple measurements that cover low to higher latitudes to investigate ionospheric and thermospheric responses to the magnetic storms of June 2015 and August 2018, including TEC measurements of ground-based receivers and the SWARM satellites, TIMED/GUVI [O/N2] ratio, Magnetometer observations, and various indices and solar wind parameters. My major concern is that the ionosphere has complex background variations and day-to-day variations, in Figures 4-8 how did the authors exactly (there are many quantitative descriptions for the responses to the storms) determine the responses to the different phases of storms from the complex TEC variability caused by multiple factors. Maybe you have done such, whereas there is no a detailed explanation in the text. A reference for the background variation of TEC may be helpful.
In the “Discussion” section, many explanations are suggested for the physical processes that cause the storm time responses, I think there are somewhat short of convinced observation evidences and detailed analyses. Figures 9-13 may be moved to the “Discussion” section to analyze the mechanisms in more detail.
Moreover,
Lines 305-309: Please explain why the reductions (enhancements) of the [O/N2] ratio result in the increment (depletion) of vTEC.
Line 317-324: You mentioned TEC enhancement and larger TEC variation. How did you confirm them to be related to the storms, not ionospheric background variations?
The PPEF and disturbed dynamo electric field are emphasized. You may further check the changes in the latitudinal structure of the low-latitude ionosphere such as EIA to analyze the effect of the zonal electric field, not only talk about the low-latitude density enhancement.
Minor comments:
Line 66-80: It is not a logical introduction.
Tables 1 and 2: Why the geomagnetic locations of the stations change between 2015 and 2018? Is that due to the secular change of the Earth’s magnetic field?
Line 100: What does “duration of the solar activity” mean?
Line 155: What does “dTEC” stand for? Please explain in the text.
Figures 7 and 8: It is better to mark the different phases of the storms in the figures. Please explain how you calculated dTEC. What is the reference value?
Line 239-240: The lowest Dst value was -203nT around 07:00 h UT on 26 August.
This cannot be seen from Figure 3. The lowest Dst did not reach -200 nT.
Figures 10 and 11: It is better to add local time information into the figures. The distribution of the plasma density depends on local time.
Figure 12: Please indicate the positive direction of the PPEF.
In the “summary”:
line 464: How did you identify ionospheric irregularities (bubbles, blobs?) from SWARM TEC measurements?
Line 469: EEJ is not a direct driver of TEC variations, the driver is ionospheric electric field.
There are many English/grammar mistakes, some suggestions (not cover all mistakes) are as follows:
Line 22: analyze -> analyzed
Line 41: trigger -> triggers
Line 67: please delete “due to PPEF”, repeat with the front
Line 68: induced -> induce
Line 75: in eastward -> are in eastward
Line 76-77: The zonal electric field corresponding to horizontal component of magnetic field
Line 101: we need satellites
Line 124: a measure of -> positively correlated with
Line 125: please delete “increases in N2 decreases electron density”, the determining factor is the [O/N2] ratio.
Line 171: This data aims -> these data aim
Line 172: is -> are
Line 251: VTEC -> vTEC, please keep consistent throughout the text.
Line 252: 42~50 TECU …
Line 254: 18~20 TECU …
Line 349: this due to -> this is due to
Citation: https://doi.org/10.5194/angeo-2022-18-RC1 -
AC1: 'Reply on RC1', munawar shah, 02 Dec 2022
Reviewer 1
Comments to “Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments” by Rasim Shahzad et al.
Ionospheric responses to magnetic storms have been widely investigated due to the remarkable influences of storms on the space environment. In this paper the authors used multiple measurements that cover low to higher latitudes to investigate ionospheric and thermospheric responses to the magnetic storms of June 2015 and August 2018, including TEC measurements of ground-based receivers and the SWARM satellites, TIMED/GUVI [O/N2] ratio, Magnetometer observations, and various indices and solar wind parameters. My major concern is that the ionosphere has complex background variations and day-to-day variations, in Figures 4-8 how did the authors exactly (there are many quantitative descriptions for the responses to the storms) determine the responses to the different phases of storms from the complex TEC variability caused by multiple factors. Maybe you have done such, whereas there is no a detailed explanation in the text. A reference for the background variation of TEC may be helpful.
In the “Discussion” section, many explanations are suggested for the physical processes that cause the storm time responses, I think there are somewhat short of convinced observation evidences and detailed analyses. Figures 9-13 may be moved to the “Discussion” section to analyze the mechanisms in more detail.
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
Moreover,
Lines 305-309: Please explain why the reductions (enhancements) of the [O/N2] ratio result in the increment (depletion) of vTEC.
Ans: Done
Line 317-324: You mentioned TEC enhancement and larger TEC variation. How did you confirm them to be related to the storms, not ionospheric background variations?
Ans: We also analyzed the data of 10 to 20 days before and after the commencement of geomagnetic storms. But, to show clear storm time variation we only utilized 2 days before and 1 day after the geomagnetic storm. As in Fig 4 to 6 of GNSS Receiver’s vTEC one can clearly see the vTEC fluctuation in various region in reference to different geomagnetic storms indicated in figure as well. Further GUVI, Magnetometer, Geomagnetic indices along with PPEF data depicted strong correlation with vTEC variation showing these variations are due to geomagnetic storms.
The PPEF and disturbed dynamo electric field are emphasized. You may further check the changes in the latitudinal structure of the low-latitude ionosphere such as EIA to analyze the effect of the zonal electric field, not only talk about the low-latitude density enhancement.
Ans: Dear reviewer, the GIM maps show clearly the EIA variations at different latitudes. The GNSS VTEC from stations at different latitudes also mean to clear the extent of variations in EIA at different latitudes. Thanks for your brief comments.
Minor comments:
Line 66-80: It is not a logical introduction.
Ans: Thank you very much. We have revised the text.
“In the equatorial and low latitudes, the electrodynamics in the ionospheric E and F regions influences the plasma distribution (Heelis, 2004). Field Aligned Current System (FACS) controls the transfer of energy and momentum from the magnetosphere to the ionosphere (Binod et al. 2017). The neutral wind dynamo induces electric fields in the low latitude regions during dayside (night side) having eastward (westward) direction (Fuller‐Rowell, 2011). The zonal electric field corresponding to horizontal component of magnetic field generates plasma upwelling due to E×B effect. As a result, negatively and positively charged particles form on top and bottom of the ionospheric E region, respectively. At an altitude of 90-130 km, the migration of electrons produces an electric current known as the equatorial electrojet (EEJ). “
Tables 1 and 2: Why the geomagnetic locations of the stations change between 2015 and 2018? Is that due to the secular change of the Earth’s magnetic field?
Ans: Yes, it is due to the secular variation of Earth’s magnetic field. In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached ~10° per year. Further, Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up to 6° per day at some time in Earth's history.
Line 100: What does “duration of the solar activity” mean?
Ans: It means time duration of geomagnetic storm from commencement of storm to final phase of geomagnetic storm i.e., recovery phase.
Line 155: What does “dTEC” stand for? Please explain in the text.
Ans: It is the deviation from quiet-time variability (dTEC)
Figures 7 and 8: It is better to mark the different phases of the storms in the figures. Please explain how you calculated dTEC. What is the reference value?
Ans: Dear reviewer, we apologize for missing descriptions: “In order to investigate the abrupt TEC anomalies during geomagnetic storms, the new empirical vTEC model of Calabia and Jin (2020, 2019) is used as quiet-time background. In this model, vTEC observables from 2003 to 2018 were reduced to a lower-dimensional through the principal component analysis, and the resulting time-expansion coefficients were parameterized in terms of solar and magnetospheric forcing, annual, and LST cycles. The quiet magnetospheric forcing is set during the geomagnetic index condition at Am=6. In this scheme, the diurnal, annual, and solar cycle variations are eliminated, and the residuals mainly show the short-term variations due to magnetospheric forcing; i.e., those variations mainly caused due to geomagnetic storms. The resulting deviation from quiet-time variability is noted here as dTEC. “
Fig 7 and 8 is updated according to storm phases.
Fig 8
Line 239-240: The lowest Dst value was -203nT around 07:00 h UT on 26 August.
This cannot be seen from Figure 3. The lowest Dst did not reach -200 nT.
Ans: It is corrected.
Figures 10 and 11: It is better to add local time information into the figures. The distribution of the plasma density depends on local time.
Ans: Dear reviewer: ‘We analyzed the storm time variations in ionosphere during different phases around the globe in UT using GNSS receivers. Therefore, for SWARM time is also in UT to confirm the observed vTEC variations. In future we will work on local time as well.’
Figure 12: Please indicate the positive direction of the PPEF.
Ans: Done.
In the “summary”:
line 464: How did you identify ionospheric irregularities (bubbles, blobs?) from SWARM TEC measurements?
Ans: Dear reviewers: ‘In present study we quantify the impact of geomagnetic storms during multiple storm phase in ionosphere GPS vTEC variations. And, SWARM is only used to verify thee variations on global scale.’
Line 469: EEJ is not a direct driver of TEC variations, the driver is ionospheric electric field.
Ans: It is corrected as EEJ>>EIA (Typing Mistake). As low and mid latitude go through storm time variations generated by fountain effect leading to strong EIA.
There are many English/grammar mistakes, some suggestions (not cover all mistakes) are as follows:
Line 22: analyze -> analyzed Done
Line 41: trigger -> triggers Done
Line 67: please delete “due to PPEF”, repeat with the front Done
Line 68: induced -> induce Done
Line 75: in eastward -> are in eastward Done
Line 76-77: The zonal electric field corresponding to horizontal component of magnetic field Done
Line 101: we need satellites Done
Line 124: a measure of -> positively correlated with Done
Line 125: please delete “increases in N2 decreases electron density”, the determining factor is the [O/N2] ratio. Done
Line 171: This data aims -> these data aim Done
Line 172: is -> are Done
Line 251: VTEC -> vTEC, please keep consistent throughout the text. Done
Line 252: 42~50 TECU … Done
Line 254: 18~20 TECU … Done
Line 349: this due to -> this is due to Done
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AC1: 'Reply on RC1', munawar shah, 02 Dec 2022
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CC1: 'Comment on angeo-2022-18', MAJID KHAN, 07 Nov 2022
The paper entitled ‘Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments’ presents important results for the storm-time ionospheric variations. These variations are clearly explained throughout the text. The paper is recommended for publications after the below changes.
Title: replace ‘responses to Geomagnetic’ to ‘responses to the Geomagnetic’.
Abstract. Show in abstract in a line the aim of this paper.
Introduction: uniform the reference style in the text. Where ever cite in the text.
Line 51-53. What seasonal changes and what is the change? Enhancement/depletion
Page 2. Line 60. Replace ‘during storm conditions’ with ‘during the storm conditions’.
Page 4. Line 99-100. Show you aim also.
Data and methods.
Change all the data links. Whether properly added. And working?
Page 4, line 118. Add reference for Kp, 0-9.
Page 5. Line 127. Replace ‘Fig. 1’ by ‘Figure 1’ and change all Fig. with Figure in the text.
Check all equations properly and their numbers also
Fig. 1. The geomagnetic line must be black or red.
Explain more Fig 10 and 11 in the context of storms different phases and their local or UT hours.
Page 10 line 223. Insert here the explanation of both the storms in which solar phase.
Check all references to correctly cited.
Conclusion. Add one bullet on the equatorial ionospheric enhancement and its relation with EEJ and PPEF.
Check all references in the list to be properly added.
Citation: https://doi.org/10.5194/angeo-2022-18-CC1 -
AC2: 'Reply on CC1', munawar shah, 02 Dec 2022
Reviewer 2
The paper entitled ‘Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments’ presents important results for the storm-time ionospheric variations. These variations are clearly explained throughout the text. The paper is recommended for publications after the below changes.
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
Title: replace ‘responses to Geomagnetic’ to ‘responses to the Geomagnetic’. Done
Abstract. Show in abstract in a line the aim of this paper. Done
Introduction: uniform the reference style in the text. Where ever cite in the text. Done
Line 51-53. What seasonal changes and what is the change? Enhancement/depletion
Ans: According to Stankov et al. 2010 and Gao et al. 2013 geomagnetic storm induce variable variation at different latitude depicting more negative storms in summer and positive storms in winter depending upon the local time of a specific region. (Stankov, S.M., Stegen, K., Warnant, R., 2010. Seasonal variations of storm-time TEC at European middle latitudes. Advances in Space Research. 48:1318–1325), (Gao, Q., Liu, L., Zhao, B., Wan, W., Zhang, M., Ning, B., 2008. Statistical study of the storm effects in middle and low latitude ionosphere in the East-Asian sector, Chinese Journal of Geophysics. 51:435–443)
Page 2. Line 60. Replace ‘during storm conditions’ with ‘during the storm conditions’. Done
Page 4. Line 99-100. Show you aim also.
Ans: it is already mentioned in line 103-105.
Data and methods.
Change all the data links. Whether properly added. And working?
Ans: All the links are working.
Page 4, line 118. Add reference for Kp, 0-9. Done
Ans:
Page 5. Line 127. Replace ‘Fig. 1’ by ‘Figure 1’ and change all Fig. with Figure in the text. Done
Check all equations properly and their numbers also Done
Fig. 1. The geomagnetic line must be black or red. Done
Ans:
Explain more Fig 10 and 11 in the context of storms different phases and their local or UT hours. Done
Ans:
Page 10 line 223. Insert here the explanation of both the storms in which solar phase. Done
Ans:
Check all references to correctly cited. Done
Conclusion. Add one bullet on the equatorial ionospheric enhancement and its relation with EEJ and PPEF. Done
Check all references in the list to be properly added. Done
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AC2: 'Reply on CC1', munawar shah, 02 Dec 2022
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RC2: 'Comment on angeo-2022-18', Anonymous Referee #2, 10 Nov 2022
The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2022-18/angeo-2022-18-RC2-supplement.pdf
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AC3: 'Reply on RC2', munawar shah, 02 Dec 2022
General comments:
Using ground and space-based multi-instruments the authors investigated the longitudinal and latitudinal variations of ionospheric total electron content and the plausible reasons during the geomagnetic storm conditions. The strength of this study is the multi-instrument data however the presentation is not clear. For example, the authors used GNSS TEC, SWARM-TEC, and TIMED- O/N2 but they did not talk about the co-incident time of these three different measurements and how these observations agree or disagree with each other. Instead, they only mention the overall changes. There are more figures but the scientific content them are not explored. Moreover, it is very hard to follow the result section because the GNSS data is for a particular location and the SWARM and TIMED-O/N2 are on the global map. First, the authors should compare these parameters where the GNSS data is available which is more important for this study then they can give additional information about other locations. In my opinion, this manuscript needs a major revision. Therefore, I recommend to the editor for a major revision. The detailed comment and suggestions are as follows:
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
In the results section:
There is no clear information about how the authors differentiate the day-to-day variation and storm-induced variations in the TEC. Moreover, the TEC variation at different locations may due to local time variations. This point should be clarified.
Ans:
What do the authors mean by anomalies? How does it differ from the daily variation? How the anomalies are defined?
Ans: Anomaly is a term used for something that is different from the normal trend. Anomalies were defined by comparing the vTEC pattern of both quiet and disturbed days with respect to different storm phases by considering the vTEC behavior at that specific time. It was observed at various region the vTEC values exhibited unusual behavior in respond geomagnetic storms through multiple sources.
The authors' wish to convey a message from the GIMs model is not clear. How much does the model agree or disagree with the observation? Clarify it.
Ans: Thank you very much for this suggestion, we have included descriptions about the model performance.
“The TEC variations in GIMs for both storms are shown in Figures 7-8. In general, the model performs very well as a quiet-time background, with deviations up to approximately ±5 TECU previous and afterwards the storms. These results are obvious in Africa and Asia, while in America the deviations are more prominent after the storm. The residuals clearly show the short-term variations due to magnetospheric forcing; i.e., those variations mainly caused due to geomagnetic storms. The deviations during the storms reach up to approximately ±20 TECU, mostly at the low latitude regions. During the storm…”
Discussion:
Lines 369-374: These are vague arguments! First of all the exact time of these three different observations should be mentioned before the comparison! At least, there should be a table that should show the VTEC of these three measurements with coinciding time.
Ans: Thank you very much for your concern, the phases of the storms are indicated in the plots to identify the time of events. We have revised the text with more appropriate descriptions.
“All the 3 sources of VTEC data used in this study, i.e. GNSS, Swarm, and IGS GIM TEC, have reflected similar responses to the storms. Several minor differences are seen, specifically between GNSS and IGS GIM TEC, mostly due to local anomalies not well represented by GIMs of TEC (Lisa et al. 2020). The PPEF and thermospheric O/N2 variations show a clear agreement with TEC variability. Smaller PPEF, O/N2 and TEC variations are detected during the 2018 storm than during the storm of 2015. Positive TEC enhancements…”
Lines 408-413: It is hard to see these results from the figures presented in this study.
Ans: With all the respect, note figure 12 is representing PPEF variation in longitude, so that the variation can be localized.
Line-by-line comments:
Line 57, The Ionospheric irregularities… unknown. These references cited here are not relevant to the above statement. Corrected
Ans:
Line 187, equation (5), in the original equation from Ley Huy and Amory-Mazaudier, did not include the Ho, and H is 𝝙H in their equation. Since the authors use the equations from other paper better to use the equation and the symbols as it is. Done
Ans:
Lines 203-210, Provide more detail about which are the stations used inside EEJ and which stations are considered as outside EEJ in this study. Done
Ans:
From Figures 2 & 3, How does the SSC are identified? I feel from the Dst of figure 2 the SSC1 should be around 18 UT but the authors marked it at 05:46 UT why?
Ans: As it is well known SSC is the sudden increase in the magnetic field on the dayside of the Earth and magnetopause compression due to its interaction with solar winds. In figure 2, at 22/05:45 a small hock is observable. During this shock, not much change was exhibited but the wind speed increases from 350-430 km/s along with IMF Bz fluctuation from northward to southward i.e., ~6nT to ~-10nT.
Line 228, Does the solar wind speed have any role in the IMF Bz variations? If not then no need the emphasis the solar wind speed in that sentence.
Ans: IMF Bz variation is not affected by the solar wind speed. Speed is mentioned in this sentence to give more detail about the solar wind parameters.
Line 251, similar intensity in which parameter?
Ans: Both storms were of comparable intensity in terms of Dst. Both storms exhibited -210<Dst<-170nT along with Kp max 8. It has been corrected as:
Line 254 remove the space between 18 and < Done
Line 280, Do the authors think 2TECu variation is an enhancement? Remember that the error is the TEC estimation itself few TECu. Comment on it.
Ans: In that specific station vTEC values vary between 1-8TECu. 2TECu was considered as an enhancement because according to previous day (i.e., quiet day) pattern vTEC was decreasing but in relation to geomagnetic storm a variable increase was observed.
Line 281, depletion: How much reduction in the TEC is considered depletion?
Ans: According to line written there, vTEC was rising after the initial phase. But afterward a sudden 3 TECu drop was observed.
Lines 305-309, Does the time of vTEC and O/N2 observations are similar? If not then the argument is not valid.
Ans: Dear reviewers: ’Using GUVI, we showed the longitudinal behavior profile to confirm the thermospheric contribution to ionosphere variations. Furthermore, GUVI provide diurnal profile. Which we compare with ionosphere variation in different regions.’
From figures 10 and 11 it is very hard to interpret the TEC variations, the TEC range from the color bar looks like a daily and latitudinal variation rather than the storm-induced variation. Comment on it. Better to make the color bar clear with more tick labels.
Ans: These variations are positively correlated with vTEC derived from various GNSS stations with respect to various geomagnetic storm phases over the globe.
More ticks have been added in both figures.
In figure 11, VTEC is negative! How is it possible?
Ans: There was a problem with ArcGIS Pro. It has been corrected.
Lines 416-417: The ionosphere…satellite data. It is well known. What is the new message here, emphasis on it?
Ans: Dear reviewers: As mentioned in the text. ‘In this work, PPEF variability has demonstrated strong influences to TEC variability. High PPEF was detected in East and West regions during both storms, depicting clear variations in Oceania and not in the American sector. As the storm commenced, Asia, Oceania, and Russia exhibited VTEC enhancements at the low- and mid-latitudes due to PPEF. Storm time variations at the low- and mid-latitudes were generated by a large fountain effect, creating a stronger EIA. In fact, many researchers (Manucci et al. 2005; Abdu et al. 2007; Sharma et al. 2011; Lu et al. 2013) have reported these effects. The ionosphere exhibited a variable response along different longitudes. This has also been confirmed by different magnitudes of PPEF and satellite data (Figure. 4-8 & 10-12).’ Using multiple satellite data, we demonstrated these variations in multiple regions and linked them to various storm phases.
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AC3: 'Reply on RC2', munawar shah, 02 Dec 2022
Status: closed
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RC1: 'Comment on angeo-2022-18', Anonymous Referee #1, 19 Oct 2022
Comments to “Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments” by Rasim Shahzad et al.
Ionospheric responses to magnetic storms have been widely investigated due to the remarkable influences of storms on the space environment. In this paper the authors used multiple measurements that cover low to higher latitudes to investigate ionospheric and thermospheric responses to the magnetic storms of June 2015 and August 2018, including TEC measurements of ground-based receivers and the SWARM satellites, TIMED/GUVI [O/N2] ratio, Magnetometer observations, and various indices and solar wind parameters. My major concern is that the ionosphere has complex background variations and day-to-day variations, in Figures 4-8 how did the authors exactly (there are many quantitative descriptions for the responses to the storms) determine the responses to the different phases of storms from the complex TEC variability caused by multiple factors. Maybe you have done such, whereas there is no a detailed explanation in the text. A reference for the background variation of TEC may be helpful.
In the “Discussion” section, many explanations are suggested for the physical processes that cause the storm time responses, I think there are somewhat short of convinced observation evidences and detailed analyses. Figures 9-13 may be moved to the “Discussion” section to analyze the mechanisms in more detail.
Moreover,
Lines 305-309: Please explain why the reductions (enhancements) of the [O/N2] ratio result in the increment (depletion) of vTEC.
Line 317-324: You mentioned TEC enhancement and larger TEC variation. How did you confirm them to be related to the storms, not ionospheric background variations?
The PPEF and disturbed dynamo electric field are emphasized. You may further check the changes in the latitudinal structure of the low-latitude ionosphere such as EIA to analyze the effect of the zonal electric field, not only talk about the low-latitude density enhancement.
Minor comments:
Line 66-80: It is not a logical introduction.
Tables 1 and 2: Why the geomagnetic locations of the stations change between 2015 and 2018? Is that due to the secular change of the Earth’s magnetic field?
Line 100: What does “duration of the solar activity” mean?
Line 155: What does “dTEC” stand for? Please explain in the text.
Figures 7 and 8: It is better to mark the different phases of the storms in the figures. Please explain how you calculated dTEC. What is the reference value?
Line 239-240: The lowest Dst value was -203nT around 07:00 h UT on 26 August.
This cannot be seen from Figure 3. The lowest Dst did not reach -200 nT.
Figures 10 and 11: It is better to add local time information into the figures. The distribution of the plasma density depends on local time.
Figure 12: Please indicate the positive direction of the PPEF.
In the “summary”:
line 464: How did you identify ionospheric irregularities (bubbles, blobs?) from SWARM TEC measurements?
Line 469: EEJ is not a direct driver of TEC variations, the driver is ionospheric electric field.
There are many English/grammar mistakes, some suggestions (not cover all mistakes) are as follows:
Line 22: analyze -> analyzed
Line 41: trigger -> triggers
Line 67: please delete “due to PPEF”, repeat with the front
Line 68: induced -> induce
Line 75: in eastward -> are in eastward
Line 76-77: The zonal electric field corresponding to horizontal component of magnetic field
Line 101: we need satellites
Line 124: a measure of -> positively correlated with
Line 125: please delete “increases in N2 decreases electron density”, the determining factor is the [O/N2] ratio.
Line 171: This data aims -> these data aim
Line 172: is -> are
Line 251: VTEC -> vTEC, please keep consistent throughout the text.
Line 252: 42~50 TECU …
Line 254: 18~20 TECU …
Line 349: this due to -> this is due to
Citation: https://doi.org/10.5194/angeo-2022-18-RC1 -
AC1: 'Reply on RC1', munawar shah, 02 Dec 2022
Reviewer 1
Comments to “Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments” by Rasim Shahzad et al.
Ionospheric responses to magnetic storms have been widely investigated due to the remarkable influences of storms on the space environment. In this paper the authors used multiple measurements that cover low to higher latitudes to investigate ionospheric and thermospheric responses to the magnetic storms of June 2015 and August 2018, including TEC measurements of ground-based receivers and the SWARM satellites, TIMED/GUVI [O/N2] ratio, Magnetometer observations, and various indices and solar wind parameters. My major concern is that the ionosphere has complex background variations and day-to-day variations, in Figures 4-8 how did the authors exactly (there are many quantitative descriptions for the responses to the storms) determine the responses to the different phases of storms from the complex TEC variability caused by multiple factors. Maybe you have done such, whereas there is no a detailed explanation in the text. A reference for the background variation of TEC may be helpful.
In the “Discussion” section, many explanations are suggested for the physical processes that cause the storm time responses, I think there are somewhat short of convinced observation evidences and detailed analyses. Figures 9-13 may be moved to the “Discussion” section to analyze the mechanisms in more detail.
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
Moreover,
Lines 305-309: Please explain why the reductions (enhancements) of the [O/N2] ratio result in the increment (depletion) of vTEC.
Ans: Done
Line 317-324: You mentioned TEC enhancement and larger TEC variation. How did you confirm them to be related to the storms, not ionospheric background variations?
Ans: We also analyzed the data of 10 to 20 days before and after the commencement of geomagnetic storms. But, to show clear storm time variation we only utilized 2 days before and 1 day after the geomagnetic storm. As in Fig 4 to 6 of GNSS Receiver’s vTEC one can clearly see the vTEC fluctuation in various region in reference to different geomagnetic storms indicated in figure as well. Further GUVI, Magnetometer, Geomagnetic indices along with PPEF data depicted strong correlation with vTEC variation showing these variations are due to geomagnetic storms.
The PPEF and disturbed dynamo electric field are emphasized. You may further check the changes in the latitudinal structure of the low-latitude ionosphere such as EIA to analyze the effect of the zonal electric field, not only talk about the low-latitude density enhancement.
Ans: Dear reviewer, the GIM maps show clearly the EIA variations at different latitudes. The GNSS VTEC from stations at different latitudes also mean to clear the extent of variations in EIA at different latitudes. Thanks for your brief comments.
Minor comments:
Line 66-80: It is not a logical introduction.
Ans: Thank you very much. We have revised the text.
“In the equatorial and low latitudes, the electrodynamics in the ionospheric E and F regions influences the plasma distribution (Heelis, 2004). Field Aligned Current System (FACS) controls the transfer of energy and momentum from the magnetosphere to the ionosphere (Binod et al. 2017). The neutral wind dynamo induces electric fields in the low latitude regions during dayside (night side) having eastward (westward) direction (Fuller‐Rowell, 2011). The zonal electric field corresponding to horizontal component of magnetic field generates plasma upwelling due to E×B effect. As a result, negatively and positively charged particles form on top and bottom of the ionospheric E region, respectively. At an altitude of 90-130 km, the migration of electrons produces an electric current known as the equatorial electrojet (EEJ). “
Tables 1 and 2: Why the geomagnetic locations of the stations change between 2015 and 2018? Is that due to the secular change of the Earth’s magnetic field?
Ans: Yes, it is due to the secular variation of Earth’s magnetic field. In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached ~10° per year. Further, Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up to 6° per day at some time in Earth's history.
Line 100: What does “duration of the solar activity” mean?
Ans: It means time duration of geomagnetic storm from commencement of storm to final phase of geomagnetic storm i.e., recovery phase.
Line 155: What does “dTEC” stand for? Please explain in the text.
Ans: It is the deviation from quiet-time variability (dTEC)
Figures 7 and 8: It is better to mark the different phases of the storms in the figures. Please explain how you calculated dTEC. What is the reference value?
Ans: Dear reviewer, we apologize for missing descriptions: “In order to investigate the abrupt TEC anomalies during geomagnetic storms, the new empirical vTEC model of Calabia and Jin (2020, 2019) is used as quiet-time background. In this model, vTEC observables from 2003 to 2018 were reduced to a lower-dimensional through the principal component analysis, and the resulting time-expansion coefficients were parameterized in terms of solar and magnetospheric forcing, annual, and LST cycles. The quiet magnetospheric forcing is set during the geomagnetic index condition at Am=6. In this scheme, the diurnal, annual, and solar cycle variations are eliminated, and the residuals mainly show the short-term variations due to magnetospheric forcing; i.e., those variations mainly caused due to geomagnetic storms. The resulting deviation from quiet-time variability is noted here as dTEC. “
Fig 7 and 8 is updated according to storm phases.
Fig 8
Line 239-240: The lowest Dst value was -203nT around 07:00 h UT on 26 August.
This cannot be seen from Figure 3. The lowest Dst did not reach -200 nT.
Ans: It is corrected.
Figures 10 and 11: It is better to add local time information into the figures. The distribution of the plasma density depends on local time.
Ans: Dear reviewer: ‘We analyzed the storm time variations in ionosphere during different phases around the globe in UT using GNSS receivers. Therefore, for SWARM time is also in UT to confirm the observed vTEC variations. In future we will work on local time as well.’
Figure 12: Please indicate the positive direction of the PPEF.
Ans: Done.
In the “summary”:
line 464: How did you identify ionospheric irregularities (bubbles, blobs?) from SWARM TEC measurements?
Ans: Dear reviewers: ‘In present study we quantify the impact of geomagnetic storms during multiple storm phase in ionosphere GPS vTEC variations. And, SWARM is only used to verify thee variations on global scale.’
Line 469: EEJ is not a direct driver of TEC variations, the driver is ionospheric electric field.
Ans: It is corrected as EEJ>>EIA (Typing Mistake). As low and mid latitude go through storm time variations generated by fountain effect leading to strong EIA.
There are many English/grammar mistakes, some suggestions (not cover all mistakes) are as follows:
Line 22: analyze -> analyzed Done
Line 41: trigger -> triggers Done
Line 67: please delete “due to PPEF”, repeat with the front Done
Line 68: induced -> induce Done
Line 75: in eastward -> are in eastward Done
Line 76-77: The zonal electric field corresponding to horizontal component of magnetic field Done
Line 101: we need satellites Done
Line 124: a measure of -> positively correlated with Done
Line 125: please delete “increases in N2 decreases electron density”, the determining factor is the [O/N2] ratio. Done
Line 171: This data aims -> these data aim Done
Line 172: is -> are Done
Line 251: VTEC -> vTEC, please keep consistent throughout the text. Done
Line 252: 42~50 TECU … Done
Line 254: 18~20 TECU … Done
Line 349: this due to -> this is due to Done
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AC1: 'Reply on RC1', munawar shah, 02 Dec 2022
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CC1: 'Comment on angeo-2022-18', MAJID KHAN, 07 Nov 2022
The paper entitled ‘Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments’ presents important results for the storm-time ionospheric variations. These variations are clearly explained throughout the text. The paper is recommended for publications after the below changes.
Title: replace ‘responses to Geomagnetic’ to ‘responses to the Geomagnetic’.
Abstract. Show in abstract in a line the aim of this paper.
Introduction: uniform the reference style in the text. Where ever cite in the text.
Line 51-53. What seasonal changes and what is the change? Enhancement/depletion
Page 2. Line 60. Replace ‘during storm conditions’ with ‘during the storm conditions’.
Page 4. Line 99-100. Show you aim also.
Data and methods.
Change all the data links. Whether properly added. And working?
Page 4, line 118. Add reference for Kp, 0-9.
Page 5. Line 127. Replace ‘Fig. 1’ by ‘Figure 1’ and change all Fig. with Figure in the text.
Check all equations properly and their numbers also
Fig. 1. The geomagnetic line must be black or red.
Explain more Fig 10 and 11 in the context of storms different phases and their local or UT hours.
Page 10 line 223. Insert here the explanation of both the storms in which solar phase.
Check all references to correctly cited.
Conclusion. Add one bullet on the equatorial ionospheric enhancement and its relation with EEJ and PPEF.
Check all references in the list to be properly added.
Citation: https://doi.org/10.5194/angeo-2022-18-CC1 -
AC2: 'Reply on CC1', munawar shah, 02 Dec 2022
Reviewer 2
The paper entitled ‘Latitudinal variations of ionospheric-thermospheric responses to Geomagnetic Storms from Multi-Instruments’ presents important results for the storm-time ionospheric variations. These variations are clearly explained throughout the text. The paper is recommended for publications after the below changes.
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
Title: replace ‘responses to Geomagnetic’ to ‘responses to the Geomagnetic’. Done
Abstract. Show in abstract in a line the aim of this paper. Done
Introduction: uniform the reference style in the text. Where ever cite in the text. Done
Line 51-53. What seasonal changes and what is the change? Enhancement/depletion
Ans: According to Stankov et al. 2010 and Gao et al. 2013 geomagnetic storm induce variable variation at different latitude depicting more negative storms in summer and positive storms in winter depending upon the local time of a specific region. (Stankov, S.M., Stegen, K., Warnant, R., 2010. Seasonal variations of storm-time TEC at European middle latitudes. Advances in Space Research. 48:1318–1325), (Gao, Q., Liu, L., Zhao, B., Wan, W., Zhang, M., Ning, B., 2008. Statistical study of the storm effects in middle and low latitude ionosphere in the East-Asian sector, Chinese Journal of Geophysics. 51:435–443)
Page 2. Line 60. Replace ‘during storm conditions’ with ‘during the storm conditions’. Done
Page 4. Line 99-100. Show you aim also.
Ans: it is already mentioned in line 103-105.
Data and methods.
Change all the data links. Whether properly added. And working?
Ans: All the links are working.
Page 4, line 118. Add reference for Kp, 0-9. Done
Ans:
Page 5. Line 127. Replace ‘Fig. 1’ by ‘Figure 1’ and change all Fig. with Figure in the text. Done
Check all equations properly and their numbers also Done
Fig. 1. The geomagnetic line must be black or red. Done
Ans:
Explain more Fig 10 and 11 in the context of storms different phases and their local or UT hours. Done
Ans:
Page 10 line 223. Insert here the explanation of both the storms in which solar phase. Done
Ans:
Check all references to correctly cited. Done
Conclusion. Add one bullet on the equatorial ionospheric enhancement and its relation with EEJ and PPEF. Done
Check all references in the list to be properly added. Done
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AC2: 'Reply on CC1', munawar shah, 02 Dec 2022
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RC2: 'Comment on angeo-2022-18', Anonymous Referee #2, 10 Nov 2022
The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2022-18/angeo-2022-18-RC2-supplement.pdf
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AC3: 'Reply on RC2', munawar shah, 02 Dec 2022
General comments:
Using ground and space-based multi-instruments the authors investigated the longitudinal and latitudinal variations of ionospheric total electron content and the plausible reasons during the geomagnetic storm conditions. The strength of this study is the multi-instrument data however the presentation is not clear. For example, the authors used GNSS TEC, SWARM-TEC, and TIMED- O/N2 but they did not talk about the co-incident time of these three different measurements and how these observations agree or disagree with each other. Instead, they only mention the overall changes. There are more figures but the scientific content them are not explored. Moreover, it is very hard to follow the result section because the GNSS data is for a particular location and the SWARM and TIMED-O/N2 are on the global map. First, the authors should compare these parameters where the GNSS data is available which is more important for this study then they can give additional information about other locations. In my opinion, this manuscript needs a major revision. Therefore, I recommend to the editor for a major revision. The detailed comment and suggestions are as follows:
Dear Reviewer thanks for your suggestion and useful comments. We have tried to improve the discussion as per your comments.
In the results section:
There is no clear information about how the authors differentiate the day-to-day variation and storm-induced variations in the TEC. Moreover, the TEC variation at different locations may due to local time variations. This point should be clarified.
Ans:
What do the authors mean by anomalies? How does it differ from the daily variation? How the anomalies are defined?
Ans: Anomaly is a term used for something that is different from the normal trend. Anomalies were defined by comparing the vTEC pattern of both quiet and disturbed days with respect to different storm phases by considering the vTEC behavior at that specific time. It was observed at various region the vTEC values exhibited unusual behavior in respond geomagnetic storms through multiple sources.
The authors' wish to convey a message from the GIMs model is not clear. How much does the model agree or disagree with the observation? Clarify it.
Ans: Thank you very much for this suggestion, we have included descriptions about the model performance.
“The TEC variations in GIMs for both storms are shown in Figures 7-8. In general, the model performs very well as a quiet-time background, with deviations up to approximately ±5 TECU previous and afterwards the storms. These results are obvious in Africa and Asia, while in America the deviations are more prominent after the storm. The residuals clearly show the short-term variations due to magnetospheric forcing; i.e., those variations mainly caused due to geomagnetic storms. The deviations during the storms reach up to approximately ±20 TECU, mostly at the low latitude regions. During the storm…”
Discussion:
Lines 369-374: These are vague arguments! First of all the exact time of these three different observations should be mentioned before the comparison! At least, there should be a table that should show the VTEC of these three measurements with coinciding time.
Ans: Thank you very much for your concern, the phases of the storms are indicated in the plots to identify the time of events. We have revised the text with more appropriate descriptions.
“All the 3 sources of VTEC data used in this study, i.e. GNSS, Swarm, and IGS GIM TEC, have reflected similar responses to the storms. Several minor differences are seen, specifically between GNSS and IGS GIM TEC, mostly due to local anomalies not well represented by GIMs of TEC (Lisa et al. 2020). The PPEF and thermospheric O/N2 variations show a clear agreement with TEC variability. Smaller PPEF, O/N2 and TEC variations are detected during the 2018 storm than during the storm of 2015. Positive TEC enhancements…”
Lines 408-413: It is hard to see these results from the figures presented in this study.
Ans: With all the respect, note figure 12 is representing PPEF variation in longitude, so that the variation can be localized.
Line-by-line comments:
Line 57, The Ionospheric irregularities… unknown. These references cited here are not relevant to the above statement. Corrected
Ans:
Line 187, equation (5), in the original equation from Ley Huy and Amory-Mazaudier, did not include the Ho, and H is 𝝙H in their equation. Since the authors use the equations from other paper better to use the equation and the symbols as it is. Done
Ans:
Lines 203-210, Provide more detail about which are the stations used inside EEJ and which stations are considered as outside EEJ in this study. Done
Ans:
From Figures 2 & 3, How does the SSC are identified? I feel from the Dst of figure 2 the SSC1 should be around 18 UT but the authors marked it at 05:46 UT why?
Ans: As it is well known SSC is the sudden increase in the magnetic field on the dayside of the Earth and magnetopause compression due to its interaction with solar winds. In figure 2, at 22/05:45 a small hock is observable. During this shock, not much change was exhibited but the wind speed increases from 350-430 km/s along with IMF Bz fluctuation from northward to southward i.e., ~6nT to ~-10nT.
Line 228, Does the solar wind speed have any role in the IMF Bz variations? If not then no need the emphasis the solar wind speed in that sentence.
Ans: IMF Bz variation is not affected by the solar wind speed. Speed is mentioned in this sentence to give more detail about the solar wind parameters.
Line 251, similar intensity in which parameter?
Ans: Both storms were of comparable intensity in terms of Dst. Both storms exhibited -210<Dst<-170nT along with Kp max 8. It has been corrected as:
Line 254 remove the space between 18 and < Done
Line 280, Do the authors think 2TECu variation is an enhancement? Remember that the error is the TEC estimation itself few TECu. Comment on it.
Ans: In that specific station vTEC values vary between 1-8TECu. 2TECu was considered as an enhancement because according to previous day (i.e., quiet day) pattern vTEC was decreasing but in relation to geomagnetic storm a variable increase was observed.
Line 281, depletion: How much reduction in the TEC is considered depletion?
Ans: According to line written there, vTEC was rising after the initial phase. But afterward a sudden 3 TECu drop was observed.
Lines 305-309, Does the time of vTEC and O/N2 observations are similar? If not then the argument is not valid.
Ans: Dear reviewers: ’Using GUVI, we showed the longitudinal behavior profile to confirm the thermospheric contribution to ionosphere variations. Furthermore, GUVI provide diurnal profile. Which we compare with ionosphere variation in different regions.’
From figures 10 and 11 it is very hard to interpret the TEC variations, the TEC range from the color bar looks like a daily and latitudinal variation rather than the storm-induced variation. Comment on it. Better to make the color bar clear with more tick labels.
Ans: These variations are positively correlated with vTEC derived from various GNSS stations with respect to various geomagnetic storm phases over the globe.
More ticks have been added in both figures.
In figure 11, VTEC is negative! How is it possible?
Ans: There was a problem with ArcGIS Pro. It has been corrected.
Lines 416-417: The ionosphere…satellite data. It is well known. What is the new message here, emphasis on it?
Ans: Dear reviewers: As mentioned in the text. ‘In this work, PPEF variability has demonstrated strong influences to TEC variability. High PPEF was detected in East and West regions during both storms, depicting clear variations in Oceania and not in the American sector. As the storm commenced, Asia, Oceania, and Russia exhibited VTEC enhancements at the low- and mid-latitudes due to PPEF. Storm time variations at the low- and mid-latitudes were generated by a large fountain effect, creating a stronger EIA. In fact, many researchers (Manucci et al. 2005; Abdu et al. 2007; Sharma et al. 2011; Lu et al. 2013) have reported these effects. The ionosphere exhibited a variable response along different longitudes. This has also been confirmed by different magnitudes of PPEF and satellite data (Figure. 4-8 & 10-12).’ Using multiple satellite data, we demonstrated these variations in multiple regions and linked them to various storm phases.
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AC3: 'Reply on RC2', munawar shah, 02 Dec 2022
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