Simultaneous ground-based and in situ Swarm observations of equatorial F-region irregularities over Jicamarca

Aol, Sharon; Buchert, Stephan; Jurua, Edward; Milla, Marco

doi:https://doi.org/10.5194/angeo-38-1063-2020

Articles | Volume 38, issue 5

https://doi.org/10.5194/angeo-38-1063-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/angeo-38-1063-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 38, issue 5

Regular paper

|

16 Oct 2020

Regular paper |

| 16 Oct 2020

Simultaneous ground-based and in situ Swarm observations of equatorial F-region irregularities over Jicamarca

Sharon Aol, Stephan Buchert, Edward Jurua, and Marco Milla

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Final revised paper (published on 16 Oct 2020)
Preprint (discussion started on 03 Dec 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'major revision', Anonymous Referee #1, 08 Jan 2020
- AC1: 'Response to referee one comments', Sharon Aol, 31 Jan 2020
RC2: 'Review of «Simultaneous Ground-based and In Situ Swarm Observations of Equatorial F-region Irregularities over Jicamarca”', Anonymous Referee #2, 17 Feb 2020
- AC2: 'Response to referee two comments', Sharon Aol, 11 Mar 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Publish subject to revisions (further review by editor and referees) (17 Mar 2020) by Keisuke Hosokawa

AR by Sharon Aol on behalf of the Authors (15 Apr 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Apr 2020) by Keisuke Hosokawa

RR by Anonymous Referee #1 (16 May 2020)

RR by Anonymous Referee #2 (09 Jun 2020)

Suggestions for revision or reasons for rejection

Review of «Simultaneous Ground-based and In Situ Swarm Observations of Equatorial F-region Irregularities over Jicamarca” by Sharon Aol et al.

General comment: The authors compare density irregularities observed in-situ by the Swarm satellites with ground-based observations of plumes made by the Jicamarca unattended long term investigations of the ionosphere and atmosphere (JULIA) radar and ionosondes. Using data between 2014 and 2018, the authors investigate whether Swarm can be used as indicator of plasma plumes/Spread F observed on the ground, and compare the statistical trends between the in-situ and ground-based instruments.
This study provides a nice confirmation that Swarm can detect plumes and Spread F and, having conjunctions from different instruments grouped in one manuscript is of significant interest. However, even though the authors attempted to address the comments from the previous reviews, the main messages and discussion are still somehow unclear. This may also partially be due to the structure of the text where observations and discussions merged, making the global arguments less clear.
Since the study is very similar to previous ones, my point of view is that the results should be discussed in more detail (especially with respect to the other, almost similar studies) and the main findings emphasized. Furthermore, some parts should be clarified.

Further details and comments are given below. (pages P and lines l refer to the final version of the manuscript)

Comment 1: Discussion

From what I understand, the authors argue that the main differences between their work and the previous ones are (very briefly summarized)
a) They study meridional structures (and that few have done this before, and DMSP was too high)
b) They used 16 Hz data (LP 2 Hz data was used before for Swarm).
c) Previous JULIA-Swarm comparison was mostly from a case study (using 2Hz)

While the “technical differences” are mentioned in the introduction (P3), there is no real substantial discussion on comparing the author’s results with the previous studies. Since the studies are similar, some more detail discussion is expected to highlight differences/similarities in the results.
E.g. of ideas of discussion points: Differences between studies based on zonal and merional? Comparison with results of DMSP? Is it actually necessary to use the 16 Hz or is 2 Hz (as done in the previous studies) sufficient? Since the scales detected by JULIA and Swarm are different anyways… etc

Comment 2: Statistical analysis
While looking at the statistical analysis and now that the authors explained how they performed their analysis, I have a few questions:

a) Comparing Fig. 8, 9, and 10, it seems like the largest occurrence of plasma plumes about 400km (so the ones that can be detected by Swarm) occur around December solstice, which also corresponds to the period with peak in mean QF. The distribution of the std(Ne) from Swarm do not seem to exhibit this pattern (but maybe the actual occurrence rate of ionospheric irregularities detected by Swarm would?). Could the authors comment on this and on the eventual implications for using Swarm as indicator of Spread F.

b) In 3.3.1, the authors only look at well-developed plumes, while in 3.3.2, all altitudes seem to be taken into account. It is not so clear to me why the authors did not only include high-altitude data in part 3.3.2 if the intention was to directly compare distributions of plumes/SF that can be detected by Swarm? Could the authors comment on this, and eventually clarify their main intention in the text?

b) The inclusion of IBI is interesting. However, the authors compare an occurrence rate (IBI) versus std(Ne). I don’t understand how this comparison is meaningful, and how the authors can claim “The binned percentage occurrence of IBI = 1 shown in Fig. 12 shows similar results to the ones shown in Fig. 11, but with lower percentage occurrence” (P18 L6). Could the authors please elaborate?

Minor comments:

0. I found several places where sentences were the same as in the sources e.g.:
-P4 L20-21: “is programmed to emit pulses of 26:6 mus duration at a repetition rate of 100 Hz”
-P4 L21-22 “This allows sampling of 200 range gates of 4 km extent from 95 to about 900 km altitude above sea level (Hysell and Burcham, 1998).”
-P6 L5-6 “The spread range at each frequency is the virtual height difference between the top and bottom of the spread echo at a particular frequency»
-P7 L8-9 (see minor comment 6.)

This is easily rectified, but fairly important, and I would advise to go through the manuscript once more in detail to check for parts that are too similar to previous articles.

1. P2 l5 and l11: Precise “equatorial”, as there are irregularities at high latitudes also.

2. P2 l15: «(Tsunoda et al. 1982)»: Is this the correct reference? (no mention of the smaller extent, it seems).

3. P5 l12: “(Ngwira et al., 2013a)”: Is this the correct reference?

4. P5 l26: “Field-aligned irregularities in the F-region are often observed between 1800 LT and 0600 LT by the JULIA radar”: Add reference.

5. P6 l17: “certainly”: I am not sure it is certain. Maybe “most likely”, or “probably”, or some alternative.

6. P7 l8-9: “Bottom-type layers do not cause strong ionogram spread F or intense radio scintillation at VHF frequencies and above” same sentence as in Hysell, 2000 except with one word removed. Modify slightly and add reference.

7. P11 l5-12: A few points are still unclear:

a) how were the conjunctions selected with respect to time?
b) By peak height, is it meant “the altitude with largest SNR?
c) RTI has been defined as Rayleigh - Taylor Instability P.2 L.10

8. P12 l14-15: “This suggests that plume structures may not have ascended to Swarm altitudes by the time the satellites passed…”: Couldn’t this actually be checked precisely, since the authors wrote they made summary plots like figure 4 for each pass?

9. P15 l5: “geomagnetic conditions”: Is it still Kp<3?

10. P19 l9: “Therefore, we presented the calculated std(Ne) per bin” : This is still unclear to me. Do the authors show the average std(Ne) per bin for the different periods, or the maxima, or do they only have one std(Ne) value per bin?

11. P17 l7: Define IBI.

12. P18 l2: The binning is different with respect to the one made for std(Ne). Is there a reason for this?

13. P18 l7: add “(…)” to Wan et al. 2018

14. P19 l29-32: “on …. Soltice”: about three months of data were used to represent the conditions at equinox or solstice, so the authors may consider to write a bit more precisely.

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ED: Publish subject to revisions (further review by editor and referees) (11 Jun 2020) by Keisuke Hosokawa

AR by Sharon Aol on behalf of the Authors (22 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Jul 2020) by Keisuke Hosokawa

RR by Anonymous Referee #2 (14 Aug 2020)

ED: Publish as is (17 Aug 2020) by Keisuke Hosokawa

Short summary

Ionospheric irregularities are a common phenomenon in the low-latitude ionosphere. In this paper, we compared simultaneous observations of plasma plumes by the JULIA radar, ionogram spread F generated from ionosonde observations installed at the Jicamarca Radio Observatory, and irregularities observed in situ by Swarm to determine whether Swarm in situ observations can be used as indicators of the presence of plasma plumes and spread F on the ground.