Dear Dr. Luo, dear co-authors,

Thank you for submitting your manuscript to the Annales Geophysicae and for your response to referees’ comments. The paper contains interesting results for ionospheric community. Nevertheless, as it was mentioned in the referees’ comments and suggestions, there are some incorrect statements and interpretations of your findings.
Let’s start from the title. One of the referees suggested modification of the title and I fully agree with his opinion. In your response to the referee’s comments you stated that “ The subject of this study is the influence of the ionospheric storm on the characteristics of HF radio waves propagating over the area of the People’s Republic of China”. The title of the manuscript should therefore reflect the aim and substance of the research carried out. You have introduced a large number of values of different solar wind, geomagnetic and ionospheric parameters, nevertheless they are not fully used for interpretation of your findings. So, my suggestion is to change the title of the manuscript and focus on the main goal “influence of ionospheric storm on HF radio wave propagation” instead of widely describing geospace storms.
On the other hand, the space weather event you are analysing in the paper, is not a CME-related event, but the event of CIR/CH HS origin combined with solar sector boundary crossing event, which could also affect geomagnetic situation. The NOAA informed that “ from midday on 30 Aug through 01 Sep, field activity increased to unsettled to G1 (minor) and G2 (moderate) levels as Earth came under the influence of a large, recurrent positive polarity CH HSS. 30 Aug saw a SSBC from a negative to a positive sector in advance of a CIR, all preceding the CH HSS. 31 Aug and 01 Sep observed active to G1 and G2 storm conditions. Wind speeds averaged about 750 km/s during this time frame with a peak of 835 km/s observed early on 01 Sep” (SWPC PRF 2296 02 September 2019). These events have a bit different characteristics and courses compared with those of the CME-origin, e.g. smaller effect on Dst index, not so well expressed single phases of the storm, longer entire duration of the disturbances and, in total, larger energy input into the Earth’s upper atmosphere (for more information, please, see Koskinen HEJ, (2011). Physics of space storms. From Solar Surface to the Earth, Springer in association with Praxis Publishing. DOI:10.1007/978-3-642-00319-6). During ionospheric storms the phases/ionospheric response (positive and negative) are usually alternating. In most cases the CIR storms have positive effect just after storm onset. Storms are usually accompanied by large- or medium-scale travelling ionospheric disturbances formed by GW that propagate from high latitudes toward the equator.
My suggestion is to compare the courses of ionospheric parameters with monthly median values or running means (or compare with the courses for quiet days near the even) to see real response to the storm-induced disturbances.
Now some minor comments. It seems that the ionospheric data you are using have some gaps, e.g. Fig.5, foF2 and h’(F2) at bout 05-08 am and 11am -15 pm. Please, don’t use a solid line to cross the data gaps. Are your ionospheric data manually checked or are coming from automatic scaling?



“The manifestations of geospace storms vary over the solar cycle, and depend on season, local time, latitude, longitude, and observational facilities” (between lines 65-70). Are you really sure that manifestation of storms depends on observation facilities?
“The main feature of this geospace storm is its duration, of up to four days.”(between lines 70-75). The duration of storms could be quite different depending on driver (from several hours up to 8-10 days). “Thus, this magnetic storm had the longest duration observed over the last few years,…” (part 135-140). This statements is also doubtful.
“To assess the ionospheric storm on the global scale, ionosonde data from the City of Moscow (55.47°N, 37.30°E), the Russian Federation, have been used.” (between 170-175). I guess that expression “global” usually is used for description of the phenomenon around all the globe and both hemispheres.
“…subsequently, a decrease from 15 x106 m–3 to to ? 106 m–3 in the course of the next three days” (between 115-120).
When concluding the referees’ comments and what has been mentioned above, I would like to inform you that the current status of your manuscript is “major revision”. One referee and me will read the manuscript once again.
If you are prepared to undertake the improvements required, please submit the revised manuscript as well as a list of changes or a rebuttal against each point, which is being raised when you submit the revised manuscript.
Kindest regards

Yours sincerely

Dalia Buresova

Dear author, dear co-authors,

The manuscript contains the results of interesting measurements and provides information about the effects of an ionospheric storm on the propagation of radio waves over a certain locality, which is useful information for the scientific community. Unfortunately, in its current form, the article still gives the impression of inconsistency: a large amount of diverse information without proper interpretation and discussion.
Please, clarify for yourself what was the main goal of your research, the results of which you wish to publish. In your responses you stated that “The subject of this study is the influence of the ionospheric storm on the characteristics of HF radio waves propagating over the area of the People’s Republic of China”. If this is indeed the case, please focus particularly on this goal. Then it is not necessary to analyze in detail the individual solar and geomagnetic parameters of the storm, because in the article you do not analyze how this or that specific parameter affected the observed changes in the propagation of radio waves. On the other hand, in the manuscript we are reading “This study provides general analysis of the 30 August–2 September 2019 geospace storm, the analysis of disturbances in the geomagnetic field and in the ionosphere, as well as the influence of the ionospheric storm on the characteristics of HF radio waves over the People's Republic of China.” If you are analysing both the storm occurrence, its course and the effects on HF radio wave propagation, then you should give information on storm characteristics, discuss the physical mechanism of storm behaviour and also how individual features/parameters of the storm affect the propagation of radio waves.
Recently, your Conclusions are focused mostly on the storm classification, parameters and changes in the ionospheric parameters. There is no convincing summary/findings on the effects on the radio wave propagation. The only finding on HF wave propagation you gave here is that “In the course of the ionospheric storm, the altitude of reflection of radio waves could exhibit sharp increases from ~150 km to ~300–310 km”. However, in your response you mentioned that this could be due to ionospheric transition from the day to the night time. Yes, it seems to be a most possible reason. To see the effects of the storm on the reflexion height, you should compare measured values with the mean values of the reflexion heights (or the values for quiet days) for the same time period.
In the Conclusions you also stated that “The geospace storm acted to notably disturb the ionospheric E region, as well as sporadic Es layer.” The Es layer is sporadic layer. It could appear during the storm, but this is not a rule. It could be formatted under quiet conditions during different seasons or time of the day and could have different duration. What you have observed, are changes in the critical frequency foEs (again, comparison with mean values or quiet time values would be useful).

Abstract and Introduction: You have newly introduced a statement “The concept that geospace storms are comprised of synergistically coupled magnetic storms, ionospheric storms, atmospheric storms, and storms in the electric field originating in the magnetosphere, the ionosphere and the atmosphere (i.e., electrical storms) was validated a few decades ago.” This is correct. Nevertheless the another sentence in the abstract says that “The geospace storm was accompanied by a moderate to strong negative ionospheric storm”, what evocates that ionospheric disturbances are out of the “synergistically coupled” system. Please, make a correction, for example “…during this geospace storm significant negative ionospheric effects were observed above China…” or so (the same for Conclusions)



Some remarks with regards to previous comments:
(8) Comment to the Authors:
“The main feature of this geospace storm is its duration, of up to four days.”(between lines 70-75). The duration of storms could be quite different depending on driver (from several hours up to 8-10 days).
Authors’ reply:
We have made a more accurate as “One of the interesting features of this geospace storm is its duration, of up to four days.”
Dear authors, I could not agree with the change you made in the sentence above (“interesting” instead of “important”). The duration of the storm in this case is not exceptional or interesting, so there is enough to state that the storm lasted four days.
The same is true for the comment (9)
(9) Comment to the Authors:
“Thus, this magnetic storm had the longest duration observed over the last few years,…” (part 135-140).
This statements is also doubtful.
Authors’ reply:
We have made a more accurate assertion: “Thus, this magnetic storm was seen to be of quite a long duration over the last few years, ”.
Again, as for its duration the storm you have analysed is not exceptional when you consider that it is a storm of CIR-origin. Usually these storms have longer (more than four days) duration when comparing with those CME-related storms and the total energy input into Earth's upper atmosphere could also be larger. Going back into last few years we had several storms with similar or longer duration both CME- or CIR-related (e.g. June and March 2015; March, May, July, September, November 2017; April, August 2018)

Please, try to modify the article once again in the light of the reviewers' recommendations. The work contains interesting experimental results. It would be good to organize the results logically, put them into context and discuss them appropriately. Then the article will be understandable and beneficial for the reader.
Kindest regards

Yours cordially
Dalia Buresova