Review of manuscript entitled “Co-seismic infrasound in the ionosphere over Central Europe from the M8.8 Kamchatka 2025 earthquake observed by Doppler sounding at record heights” by Chum et al.

This study reported a unique observation of co-seismic infrasound wave signature at an unprecedented high altitude of the ionosphere by the continuous Doppler sounding systems (CDSS) in Czechia and Slovakia. This paper is novel in two aspects: (1) Co-seismic infrasound waves can propagate upward to the altitude of ionospheric F layer. (2) The ionospheric perturbations observed by Doppler sounder is an effective characterization of the response to earthquakes. The authors confirmed the presence of infrasound wave using ray tracing simulation, and also revealed the characteristics and underlying mechanisms of the upward propagation of infrasound waves generated by the earthquake. This paper should be published after considering the follow comments.

1. The authors should emphasize the significance of the findings of this paper in abstract and conclusion. e.g., promoting community’s understanding of seismic wave propagation, or providing new results or methods for monitoring atmospheric and ionospheric responses to the earthquake.
2. Line 315: The authors indicated the reasonableness of the observed infrasound wave amplitude by the approximately similar time and frequency between the observed and simulated waveforms. However, there is obvious phase delay between them. Please provide some explanation to clarify.
3. I do not quite understand the purpose of checking the measurements of OH airglow emissions. As the author indicated, the high-frequency infrasound wave also presents in the lower altitudes but cannot reach the ionospheric F layer height, but they showed no significant changes in the OH temperature related to infrasound waves.
4. The authors should mention the limitation in the discussion/conclusion that the detection of co-seismic infrasound waves by Doppler sounder needs a nearby ionosonde to provide the electron density gradient at the reflection height.

Comment on the revised manuscript entitled "Co-seismic infrasound in the ionosphere over Central Europe from the M8.8 Kamchatka 2025 earthquake observed by Doppler sounding at record heights" by Chum et al. 

This manuscript presents observations of co-seismic ionospheric disturbances associated with the 29 July 2025 M8.8 Kamchatka earthquake using continuous Doppler sounding systems in Czechia and Slovakia. The authors report the detection of ionospheric signatures at reflection heights of approximately 340 km, which they claim to represent the highest-altitude observation of co-seismic infrasound by HF Doppler sounding to date. The study combines Doppler observations, digisonde measurements, ray-tracing calculations, and full-wave numerical simulations to investigate the propagation and attenuation of earthquake-generated infrasound waves.

The topic is timely and relevant to the communities studying lithosphere--atmosphere--ionosphere coupling and coseismic ionospheric disturbances. The dataset is valuable, and the reported observations are potentially significant. In particular, the apparent detection of co-seismic infrasound at unusually high altitudes and the discussion of frequency-dependent attenuation during upward propagation are interesting and worthy of publication.

However, I would ask the authors to carefully consider the following points before the manuscript is accepted for publication.

1. Discussion of the OH airglow observations

In Lines 353--358, the authors state that "The time resolution of OH temperature measurement by GRIPS is 15 s. This sampling frequency … using the continuous Wavelet Transform (not shown)." This sentences showed that the temporal resolution of the OH airglow observations is insufficient to resolve the higher-frequency perturbations expected in association with the earthquake. If so, the meanings for discussing the OH airglow results is not clear.

OH airglow observations would be highly valuable if they were capable of detecting temporal variations similar to those reported by Snively et al. (2013). However, if the time resolution used in this study is unable to resolve such variations, the scientific value of presenting and discussing these observations becomes questionable. The authors should therefore provide a stronger justification for including the OH airglow results or consider removing this section from the manuscript.

2. Discussion of the Swarm satellite data

The inclusion of the Swarm satellite analysis also appears unnecessary. It should have been evident from a preliminary inspection of the satellite trajectories that no Swarm spacecraft passed sufficiently close to the region of interest during the period investigated in this study. Consequently, the absence of relevant observations does not provide meaningful information regarding the phenomenon under investigation.

Therefore, there appears to be little justification for describing the Swarm data in either the Data section or the Results section. Unless these observations contribute directly to the scientific objectives of the study, I recommend removing them in order to improve the focus and conciseness of the manuscript.

If the authors wish to incorporate additional datasets in addition to the Doppler sounding observations, GNSS-TEC measurements would likely provide more useful information. In fact, TEC observations are already discussed in the Introduction as a powerful tool for investigating ionospheric disturbances associated with seismic events. Compared with the OH airglow and Swarm datasets presented here, TEC measurements would be expected to provide more direct information on the spatial extent, propagation characteristics, and amplitude of the ionospheric response. Therefore, I encourage the authors to consider incorporating TEC observations, if available, rather than presenting datasets that do not substantially constrain the interpretation of the event.

3. Interpretation of Figure 2

According to Equation (2), the plasma vertical velocity, w_p, should be smaller than the neutral vertical velocity, w. However, Figure 2 appears to show the opposite relationship, with w being smaller than w_p. The reason for this apparent discrepancy is unclear. The authors should explain why the relationship shown in Figure 2 differs from that expected from Equation (2), or clarify whether there is a misunderstanding regarding the definition, derivation, or presentation of these quantities.

In addition, Figure 2(c) contains several different quantities, including the observed plasma vertical velocity (w_p), the neutral velocity (w) derived from the observations, the numerically simulated neutral velocity, and the result obtained over Slovakia, which is shown as a green dashed line. As a result, the figure is rather crowded and difficult to interpret.

In particular, the green dashed line is difficult to distinguish from the other curves. I recommend improving the figure by using more clearly distinguishable colours, line styles, and/or line widths, and by enhancing the overall readability of the plot. Since the scientific interpretation relies heavily on comparisons among these datasets, the figure should be redesigned so that all curves can be readily distinguished by the reader.