the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Sep 2022
Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E layer
Abstract. Based on the global COSMIC occultation data, the latitudinal dependence of the geomagnetic and solar activity effect on the sporadic-E (Es) layer is investigated. Statistical results demonstrate that the relationship between Es layer occurrence rate and geomagnetic activity shows no correlation in low geomagnetic latitudes, a negative correlation in middle geomagnetic latitudes, and a positive correlation in high geomagnetic latitudes. The decrease in Es layer occurrence rate during geomagnetic activity in middle geomagnetic latitudes may be due to the descending meteor rate caused by the atmospheric density change during the geomagnetic storm. While the increase in Es layer occurrence rate in high geomagnetic latitudes is mostly related to the ionospheric electric field change driven by the international magnetic field (IMF) embedded within the solar wind. Solar activity effect on the Es layer also presents latitudinal dependence, with negative correlation in low and middle geomagnetic latitudes and positive correlation in high geomagnetic latitudes. The negative correlation may be owing to the negative correlation between meteor rate and solar activity revealed by many previous studies. The positive correlation in high geomagnetic latitudes is mostly related to the enhanced IMF during solar maximum.
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RC1: 'Comment on acp-2022-534', Anonymous Referee #1, 11 Oct 2022
Referee comments on the paper by Q. Tang et al., entitled "Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E layer", submitted to Atmospheric Chemistry and Physics.
The paper investigates the latitudinal dependence of the geomagnetic and solar activity effect on the sporadic-E layer. While the authors declared that the Es layer occurrence rate shows a positive correlation with geomagnetic Kp index at high geomagnetic latitudes, a negative correlation at middle latitudes, and no correlation at low latitudes, no quantitative analyses were conducted in the paper to show how significant the correlations are. It is some kind of arbitrary to give this conclusion simply from bar graphs in Figures 3 & 6. Figure 8 is confusing as the IMF strength is related to the F10.7, but how is the Es layer occurrence rate related to the variation of IMF?
Even on the basis of Figure 3, does the left side on the top panel (80-90N) show a negative correlation rather than a positive correlation? Besides, what makes the Es layer occurrence rate between 30° S to 60° S first presents a negative correlation with solar activity and then presents a positive correlation after the solar F10.7 index exceeds a certain value in Figure 6? The authors explained that the increasing trend of Es occurrence rate could be related to the low intensive Es layers formed from molecular ions and the decreasing trend of Es occurrence rate could be related to the high-intensive Es layers formed from metallic ions. That's not convincing. Would the authors expect opposite correlation results for the low intensive Es layers in winter hemisphere and the high-intensive Es layers in summer hemisphere? I think it is attributed to the South Atlantic Anomaly influence on the Es layer spanning from −50° to 0° geographic latitude.
Overall, more additional analyses need to be done. The discussion and conclusions are speculative. The response of the Es layer to solar activity is dependent on the interaction of photochemical reactions, chemical reactions and dynamics process in the MLT. I encourage the authors to conduct more analyses of observations and investigate the response of metallic ions and atoms in the E region in the model (i.e., Whole Atmosphere Community Climate Model with metallic chemistry) to consider the solar radiation effects on the photo-ionization and chemical reactions of neutrals and ions. The simulation results are helpful to understand the key mechanism of the variations of Es layer with F10.7 index and latitude in observations.
Citation: https://doi.org/10.5194/acp-2022-534-RC1 -
RC2: 'Comment on acp-2022-534', Anonymous Referee #2, 04 Nov 2022
Referee comment on “Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E layer” by Tang et al.
The paper presents analyses of the global S4 irregularity index distribution using S4 data from 2007-2018 as downloaded from the COSMIC Data Analysis and Archive Center. The authors claim that S4 above a certain threshold represents the occurrence of sporadic E (Es) layers. In the paper, a seasonal climatology is presented, and the manuscript includes an attempt to analyze the connection of Es occurrence with magnetic variability and the solar cycle.
The manuscript shows several weaknesses. An important one concerns the interpretation of S4 as Es occurrence. In section 2 it is described that simply a S4 index maximum > 0.3 is taken as the signature of the Es layer. Have there been additional criteria applied, or how do the authors know that the signal is not due to other irregularities or artefacts? Of course, the overall long-term distribution of S4 is similar to the one known for Es as shown in Fig. 1, and this information is not new. But, as shown in Fig. 2, for example, in magnetically disturbed cases the S4 distribution becomes very irregular and it is unclear how much of it is owing to Es then. Thus, a more critical analysis of S4 in terms of Es occurrence is necessary, or, if it had been done, must be described in more detail.
Another concern is related to the analysis and interpretation. The authors simply present long-term mean distributions of S4 without any statistical analysis and interpretation. On several occasions, the authors write of correlation or significance, but do not provide correlation coefficients or significance levels. Not even the numbers of used occultations for the different seasons, latitude ranges, or magnetic or solar ranges are provided. Given in particular that the magnetically disturbed cases are more rare than the quiet ones, the differences shown in Fig. 3 may be insignificant, if they relate to Es at all. The analyses of magnetic and solar influence is obviously done without consideration of the seasonal cycle. This would mean that any possible effect if dominated by the respective summer, does this have an influence of the results?
More minor issues relate to the presentation and discussion of the results. What is the use of not simply showing height-time cross-sections in Figs. 1, 2, and 5? A disadvantage of the present form is that for low altitudes the diurnal cycle is not well visible. And how have the spirals in Fig. 1 been calculated? In my view, this presentation can only show whether diurnal or semidiurnal variability is dominating, but this has been shown before, including higher order tidal variability. In Fig. 1, the seasons should be presented as boreal spring, summer, etc., otherwise it is incorrect for the southern hemisphere. Close inspection of Figs. 4 and 7 show some slight differences to Figs. 3 and 6, so for example, in Fig. 6, 10-20N, the occurrence rates decreases with F10.7 while in Fig. 7 it increases again for high solar activity. A further point is the presentation of the IMF in Fig. 8. IMF is somehow related to the solar cycle, but shows a delay with larger values during the declining phase. Therefore, if the authors claim that the Es solar variability could be due to IMF variations, they should repeat their analyses using IMF instead of F10.7.
To summarize, I have some concern of the validity of the analysis method, at least when low numbers of occultations are used, and the statistical analysis of the results is by far not sufficient. The paper is probably hastily written, as there are many typos and other errors, which would have been visible by a careful check. If the authors can resolve the concerns about the Es analysis method, and provide a much more thorough statistical analysis, more care should be given to the presentation in the manuscript.
Citation: https://doi.org/10.5194/acp-2022-534-RC2 -
RC3: 'Comment on acp-2022-534', Anonymous Referee #3, 25 Nov 2022
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-534/acp-2022-534-RC3-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on acp-2022-534', Anonymous Referee #1, 11 Oct 2022
Referee comments on the paper by Q. Tang et al., entitled "Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E layer", submitted to Atmospheric Chemistry and Physics.
The paper investigates the latitudinal dependence of the geomagnetic and solar activity effect on the sporadic-E layer. While the authors declared that the Es layer occurrence rate shows a positive correlation with geomagnetic Kp index at high geomagnetic latitudes, a negative correlation at middle latitudes, and no correlation at low latitudes, no quantitative analyses were conducted in the paper to show how significant the correlations are. It is some kind of arbitrary to give this conclusion simply from bar graphs in Figures 3 & 6. Figure 8 is confusing as the IMF strength is related to the F10.7, but how is the Es layer occurrence rate related to the variation of IMF?
Even on the basis of Figure 3, does the left side on the top panel (80-90N) show a negative correlation rather than a positive correlation? Besides, what makes the Es layer occurrence rate between 30° S to 60° S first presents a negative correlation with solar activity and then presents a positive correlation after the solar F10.7 index exceeds a certain value in Figure 6? The authors explained that the increasing trend of Es occurrence rate could be related to the low intensive Es layers formed from molecular ions and the decreasing trend of Es occurrence rate could be related to the high-intensive Es layers formed from metallic ions. That's not convincing. Would the authors expect opposite correlation results for the low intensive Es layers in winter hemisphere and the high-intensive Es layers in summer hemisphere? I think it is attributed to the South Atlantic Anomaly influence on the Es layer spanning from −50° to 0° geographic latitude.
Overall, more additional analyses need to be done. The discussion and conclusions are speculative. The response of the Es layer to solar activity is dependent on the interaction of photochemical reactions, chemical reactions and dynamics process in the MLT. I encourage the authors to conduct more analyses of observations and investigate the response of metallic ions and atoms in the E region in the model (i.e., Whole Atmosphere Community Climate Model with metallic chemistry) to consider the solar radiation effects on the photo-ionization and chemical reactions of neutrals and ions. The simulation results are helpful to understand the key mechanism of the variations of Es layer with F10.7 index and latitude in observations.
Citation: https://doi.org/10.5194/acp-2022-534-RC1 -
RC2: 'Comment on acp-2022-534', Anonymous Referee #2, 04 Nov 2022
Referee comment on “Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E layer” by Tang et al.
The paper presents analyses of the global S4 irregularity index distribution using S4 data from 2007-2018 as downloaded from the COSMIC Data Analysis and Archive Center. The authors claim that S4 above a certain threshold represents the occurrence of sporadic E (Es) layers. In the paper, a seasonal climatology is presented, and the manuscript includes an attempt to analyze the connection of Es occurrence with magnetic variability and the solar cycle.
The manuscript shows several weaknesses. An important one concerns the interpretation of S4 as Es occurrence. In section 2 it is described that simply a S4 index maximum > 0.3 is taken as the signature of the Es layer. Have there been additional criteria applied, or how do the authors know that the signal is not due to other irregularities or artefacts? Of course, the overall long-term distribution of S4 is similar to the one known for Es as shown in Fig. 1, and this information is not new. But, as shown in Fig. 2, for example, in magnetically disturbed cases the S4 distribution becomes very irregular and it is unclear how much of it is owing to Es then. Thus, a more critical analysis of S4 in terms of Es occurrence is necessary, or, if it had been done, must be described in more detail.
Another concern is related to the analysis and interpretation. The authors simply present long-term mean distributions of S4 without any statistical analysis and interpretation. On several occasions, the authors write of correlation or significance, but do not provide correlation coefficients or significance levels. Not even the numbers of used occultations for the different seasons, latitude ranges, or magnetic or solar ranges are provided. Given in particular that the magnetically disturbed cases are more rare than the quiet ones, the differences shown in Fig. 3 may be insignificant, if they relate to Es at all. The analyses of magnetic and solar influence is obviously done without consideration of the seasonal cycle. This would mean that any possible effect if dominated by the respective summer, does this have an influence of the results?
More minor issues relate to the presentation and discussion of the results. What is the use of not simply showing height-time cross-sections in Figs. 1, 2, and 5? A disadvantage of the present form is that for low altitudes the diurnal cycle is not well visible. And how have the spirals in Fig. 1 been calculated? In my view, this presentation can only show whether diurnal or semidiurnal variability is dominating, but this has been shown before, including higher order tidal variability. In Fig. 1, the seasons should be presented as boreal spring, summer, etc., otherwise it is incorrect for the southern hemisphere. Close inspection of Figs. 4 and 7 show some slight differences to Figs. 3 and 6, so for example, in Fig. 6, 10-20N, the occurrence rates decreases with F10.7 while in Fig. 7 it increases again for high solar activity. A further point is the presentation of the IMF in Fig. 8. IMF is somehow related to the solar cycle, but shows a delay with larger values during the declining phase. Therefore, if the authors claim that the Es solar variability could be due to IMF variations, they should repeat their analyses using IMF instead of F10.7.
To summarize, I have some concern of the validity of the analysis method, at least when low numbers of occultations are used, and the statistical analysis of the results is by far not sufficient. The paper is probably hastily written, as there are many typos and other errors, which would have been visible by a careful check. If the authors can resolve the concerns about the Es analysis method, and provide a much more thorough statistical analysis, more care should be given to the presentation in the manuscript.
Citation: https://doi.org/10.5194/acp-2022-534-RC2 -
RC3: 'Comment on acp-2022-534', Anonymous Referee #3, 25 Nov 2022
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-534/acp-2022-534-RC3-supplement.pdf
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