Comments

This paper compares the GNSS observations (both ground-based zenith TEC and radio occultation observations) to the numerical simulation of the rocket exhaust depletion (RED). RED has become an important issue given that there are almost rocket launches on daily basis in the modern era. The authors perform the observation and simulation on a specific event and their observations show clear RED effect in the ionosphere electron density. Their simulations also show very nice 3-D structure of the RED effects in the ionosphere with the clear depleted plasma structure. The literature review given by the authors is also comprehensive. Although the presented results look good as well as the literature review. There are some places require further improvements. Literature review is generally good but some important aspects were overlooked. For example, 3-D structure were previous given by Park et al. (2022) but the authors did not mention it well making a wrong impression that this study is the first one to give 3-D structure of RED, which is not true. Secondly, simulation works similar to this study were carried out by Furuya and Heki (2008) but was not well mentioned and discussed with the simulations done in this study. I think all these aspects need to be addressed seriously for evaluation of whether this study is warranted for publication. I put the specific comments as follows.

1. Lines 85-89, authors state that “Park et al. (2022) also utilized the GOLD imager, Madrigal TEC, and multiple Low-Earth-Orbit satellites, with COSMIC-2 data revealing an increase in ionospheric slab thickness at the depletion center, indirectly supporting vertical structure analysis. However, the 3D structure of rocket-exhausted electron density depletion remains unclear.” Also, in Lines 111-112, it is stated “The gridded data products derived from COSMIC occultation observations have been used in rocket‐induced depletion (RED) studies (Park et al., 2022).”

I think the authors miss out what the COSMIC-2 data were utilized in Park et al. (2022). It was the data assimilation data product of COSMIC-2, which has 3-D structure of the ionosphere. As Park et al. (2022) did provide altitudinal variations of REDs for their event, it is not for the first time the authors provide the 3-D results. In fact the Abel inversion of the electron density profile provided by the standard data output of COSMIC might be errouneous at lower altitudes (lower than ~250 km altitudes) due to its assumptions of spherical symmetry over a wide area of ionosphere (Yue et al., 2010; Liu et al., 2010). The RED generation of the density depltion on the other hand is an asymmetry density structure and therefore the actual depth/strength of the RED might not be precised using Abel inversion of the radio occultation observations. This altitude is also roughly similar to that the authors reported, so some cautious or discussion is also necessary.

Ref.

Yue, X., Schreiner, W. S., Lei, J., Sokolovskiy, S. V., Rocken, C., Hunt, D. C., and Kuo, Y.-H.: Error analysis of Abel retrieved electron density profiles from radio occultation measurements, Ann. Geophys., 28, 217–222, https://doi.org/10.5194/angeo-28-217-2010, 2010.

Liu, J. Y.,  C. Y. Lin,  C. H. Lin,  H. F. Tsai,  S. C. Solomon,  Y. Y. Sun,  I. T. Lee,  W. S. Schreiner, and  Y. H. Kuo(2010),  Artificial plasma cave in the low-latitude ionosphere results from the radio occultation inversion of the FORMOSAT-3/COSMIC, J. Geophys. Res.,  115, A07319, doi:10.1029/2009JA015079.

2. Lines 115-116, the authors claimed that “A detailed assessment of the feasibility and reliability of COSMIC occultation data can be found in Yan et al. (2022). In this study, we utilize the electron density and total electron content (TEC).” I assume they refer to this one from their Reference list.

Yan, X., Yu, T., and Xia, C.: Limb Sounders Tracking Tsunami-Induced Perturbations from the Stratosphere to the Ionosphere. Remote Sensing, 14(21), 5543. https://doi.org/10.3390/rs14215543, 2022.

However, this one is clearly not for validation of COSMIC radio occultation, two more suitable references validating COSMIC-1 and COSMIC-2 are provided as follows.

For COSMIC-1:

Lei, J., et al. (2007),  Comparison of COSMIC ionospheric measurements with ground-based observations and model predictions: Preliminary results, J. Geophys. Res.,  112, A07308, doi:10.1029/2006JA012240.

COSMIC-2:

Lin, C.-Y.,  Lin, C. C.-H.,  Liu, J.-Y.,  Rajesh, P. K.,  Matsuo, T.,  Chou, M.-Y., et al. (2020).  The early results and validation of FORMOSAT-7/COSMIC-2 space weather products: Global ionospheric specification and Ne-aided Abel electron density profile. Journal of Geophysical Research: Space Physics,  125, e2020JA028028. https://doi.org/10.1029/2020JA028028

3. In the comparison of the simulations and the observed RED, the discrepancy between observation and simulation was attributed to the background ionosphere applied in the simulation, which is from IRI. It is well understood that IRI output would not match to realistic ionosphere. But a good comparison can be made by percentage of the depletion. Also, the assumption of the H2O diffusion shall be different from reality. I think a better comparison shall be made by the authors by performing various simulation task to find out what the most suitable diffusion parameter might be for the density depletion to better agree with the observation. In this way, the authors or the readers could know how far off the assumption of diffusion given by Bernhardt (1976) to the reality. In the current version, simply compare the simulation with observation and give hypothesis to the discrepancy is actually not very helpful to better understandings of the underlying physics.

4. Furuya and Heki (2008) did perform similar simulation and compare their results to observations of GNSS-TEC. Any new insights from this study on top of Furuya and Heki (2008)? The authors may state the differences between the then study to this latest one to better describe the novelty of this study. Maybe the modeling is more comprehensive in this study? Maybe the electrodynamics is included in this study? What is the advantage of this study to the one published in 2008?