Global GNSS-RO Electron Density in the Lower Ionosphere

Round 1

Reviewer 1 Report

See the attached PDF file.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Article

Global GNSS-RO Electron Density in the Lower Ionosphere

Dong L. Wu ,Daniel J. Emmons, and Nimalan Swarnalingam

 

The paper reports “a robust algorithm is developed to retrieve global D/E-region N_e from the high-rate GNSS radio occultation (RO) data, to take advantage of improved spatiotemporal coverage from recent SmallSat/CubeSat constellations.” The proposed algorithm is based on the fitting of a linear function to the observed quantities, after a simple transformation

 

This is a research with interest to extract information on the lower ionosphere, and consequently it could be useful to the ionospheric community. I think that the paper includes too many details which makes the paper too long. If the purpose is to  show a method and its utility, probably it should try to focus into the standard paradigm: observables, model, inversion, errors...But this is just an opinion.

 

The following are some comments on this paper.

 

Main Concerns:

 

This reviewer considers that the section Data and Methods should be clarified. It should be explained the physical meaning of the concept “excess phase” in its first appearance in line 105.

This excess phase is related later, in Equation (1) to the TEC along the path, while the observed “excess phase delay” in a RO experiment corresponds to a different concept.

This reviewer understands that the method is summarized in Equations (5),(7) and (8) to provide the derived observables \Delta hTEC, which are considered the input for the characterization of the of the electron density in the lower ionosphere, discussed in Section (2.3.1). If this understanding is correct, the authors could reduce greatly the length of the Section 2.1, and to improve the clarity of the method proposed.

Because the effects on the ionospheric delays are bigger for the signals at the lower band, the authors should justify their choice of L1 in the Equations (5), (7) and (8). Perhaps showing a comparison between both (L1 and L2) possibilities could be useful to the reader.

 

 

• Figure 1. The \phi symbol do not appears in this Figure. It is confusing.

• RIF should be RIE in line 283

• The authors very often refer to atmospheric bending (see line 175) something that is a delay. In my opinion this is confusing, as bending is an angular quantity. This should be addressed in the different instances where the term bending appears.

• But, because as the authors accept (line 193) that the dominant term is the ionospheric delay, it could be omitted the consideration of the “bending delay” term, as it is not relevant. It is opinion of this reviewer that the RO community that the relevant aspect to explain ionospheric delays is the TEC encountered by the signal and not its bending. See for instance https://www.romsaf.org/general-documents/rsr/rsr_17.pdf,  Note 1, page 9.

• Figure 2. What are the red lines in the right panels?

 

 

 

Author Response

please our responses in the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper describe the retrievel of Ne in the ionosphere D and E region, which is an area that has been relatively ignored, but still important. Using the RO-measured data, they carried out the bottom Ne retrieval down to 60 to 90 km. With the retrieved data, they give the seasonal, latitudinal, local-time and solar-cycle variations of Ne in the bottom ionosphere. The work can be an important contribution to the Aeronomy and make up the shortage of the understanding of the bottom ionosphere. I recommend the paper to have a minor revison before it is suitable for publication

 

Line 64-78 the author shall also acknowledge the Es studies carried out by local instrument and add the corresponding references such as the following

 

Yuan, T., Wang, J., Cai, X., Sojka, J., Rice, D., Oberheide, J., and Criddle, N. (2014), Investigation of the seasonal and local time variations of the high-altitude sporadic Na layer (Na_s) formation and the associated midlatitude descending E layer (E_s) in lower E region, J. Geophys. Res. Space Physics, 119, 5985– 5999, doi:10.1002/2014JA019942.

 

Tang, Q., Zhou, C., Liu, H., Liu, Y., Zhao, J., Yu, Z., et al. (2021). The possible role of turbopause on sporadic-E layer formation at middle and low latitudes. Space Weather, 19, e2021SW002883. https://doi.org/10.1029/2021SW002883

Author Response

please our responses in the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed the points of my previous review.

Author Response

We made a substantial editing on the manuscript to improve English and correct grammatical errors. The changes are reflected in the new revision. 

Reviewer 2 Report

The labels in Figure 1 still are wrong. The authors indicate that they are trying to solve this issue with the editors. In fact the Figure that they include in their rebuttal letter seems correct. This should be solved.

Author Response

We followed the editor's suggestion to replace the figure with a screenshot picture. Hope this works.