This paper performed MHD simulations with two kinds of code, EUHFORIA and Gorgon-Space, to study the responses of Earth's magnetosphere and ionosphere to two CMEs that caused geomagnetic storms. EUHFORIA is for predicting the arrival time at Earth of a CME ejected from Sun, while Gorgon-Space is for simulating the magnetospheric and ionospheric responses to the solar wind and CMEs. Combining the two simulations, the authors attempted to show the differences in magnetospheric and ionospheric responses between the two CMEs. The topic is important for understanding space weather and developing its forecast, and the results are potentially interesting.

However, I do not think that this manuscript is well written, so I cannot recommend accepting this paper for publication in its present form. First, the new points of this paper are not clear to me. They should be clearly stated and discussed in the paper. Second, the authors discuss the magnetospheric and ionospheric responses to two CMEs, but the definitions of the two CMEs are not adequately stated, and the data or simulation results are not sufficiently shown. In particular, this manuscript does not show the solar wind data for the second CME (CME2) and the simulation results of the ionosphere in the Southern Hemisphere listed in the conclusion section as main results of this paper. Hence, it is difficult to understand the simulation results of the causal relationship between the CMEs and the magnetospheric and ionospheric changes and to understand the differences between the two hemispheres.

Specific comments:

Line 8 in the abstract: The authors mention CME1 without definition. What is CME1 should be explained, or the word CME1 should be reworded.

Lines 127-136: In this paragraph, the authors mention the two specific CMEs for this study, CME1 and CME2, without any explanations. Please reword CME1 and CME2 or explain them briefly here, and then explain these CMEs in more detail in the following section with appropriate figures of the solar wind data and the corresponding Kp. The authors may have shown the figure and explain the CMEs in another paper, but the main points should be repeated here so that this readers do not have to refer to the previous paper.

Lines 162-180 and Figures 1 and 3: Figure 1 shows Kp predicted by this study. Kp has three peaks, but I could not understand which Kp changes the authors discuss in this paper. CME1 seems to correspond to the second peak at ~0 UT on 23 June, but the Kp change associated with CME2 seems to be out of range of this figure. Please specify not only the date but also the time of CMEs' arrival and the associated Kp increase and show the figure for the entire interval of interest.

On the other hand, Figure 3 show the solar wind data (simulation input data), but it seems to be only for about 1 day from the beginning of the simulation although the authors seem to have performed the simulation for more than 10 days including the multiple CMEs. Again, please show the figure of the solar wind for the entire interval of interest. In addition, are the solar wind data shown in Figure 3 from real observations? I think that the horizontal axis is simulation time in hour, so is it correct that the data themselves are real observations from a spacecraft, but the time is modified according to the prediction by EUHFORIA? Please explain the detail about that, or how EUHFORIA, Gorgon-Space, and real solar wind observations are connected.

Furthermore, I checked the real solar wind (OMNI) data. As the authors describe, a few CMEs arrived at Earth on 21-23 June 2015, but it is not clear to me which CME the authors discuss in this paper or which is CME1. On the other hand, it seems to me that no CME arrived at Earth on 28 June 2015 (the arrival time of CME2 according to the main text), that is, large changes in the solar wind speed, dynamic pressure, magnetic field peculiar to a CME are not seen. I guess there are some time differences between the observations and the EUHFORIA simulation results. After all, it is necessary to show the solar wind data, state the definitions of CME1 and CME2 clearly, and furthermore make some comments on the time differences between the observations and the simulation results.

Figures 4 and 6 caption: The second sentence says that the first CME arrived at Earth at 00:03 UT on 23 June 2015. However, looking at the predicted Kp index shown in Figure 1, it began to increase before that, around ~20 UT on 22 June 2015, implying that this CME arrived then. Check the simulation results again and modify the description, if necessary.

Line 177: "23 June" should be "22 June".

Lines 196-200 (Figure 5), lines 216-219 (Figure 7), lines 281-285 (Figures 9), and lines 299-301 (Figure 11): The caption says that the second CME arrived at Earth at 12:52 UT on 28 June 2015, but it is after the interval shown in Figure 1. In addition, Figures 5, 7, 9, and 11 show that unlike CME1, the changes associated with CME2 are small, which do not seem to be due to the storm main phase. Are these results really due to the CME or the storm? Please reexamine the observation and simulation data, show the solar wind and Kp data for the entire interval of interest, and describe when CME2 occurred specifically.

Lines 276-277: The authors wrote that Fig. 8d shows the difference in field-aligned current between the Northern and Southern Hemispheres. The plots of the Southern Hemisphere should also be shown.

Minor comments:

Lines 28-29: In my understanding, sudden impulse indicates magnetospheric compression due to sudden enhancement of the solar wind dynamic pressure in general, irrespective of whether a geomagnetic storm follows. If a geomagnetic storm occurs after sudden impulse, it is also called storm sudden commencement. 

Line 172: towards --> along

Lines 249-250: The field-aligned current and J of JxB at the end of this sentence should be different. This part would need to be reworded to avoid confusion.

Line 278: along --> across ? (Convection should be perpendicular to the magnetic field.)

Lines 296-297: Perhaps the elevated cross-polar cap potential (enhanced large-scale convection) was associated with the storm, not substorms.

Other minor corrections:

Line 125: Typo "?".

Figures 4 and 5 captions: solar wind pressure --> thermal pressure

Figures 6 and 7 captions, and lines 207 and 216: solar wind velocity --> velocity (because the magnetosphere is included)

Line 232: Move equation (6) to the appropriate place.

Line 248: Equation 7 --> 6

Line 273: zero latitude ... a latitude --> zero colatitude ... a colatitude (or correct the values of latitude from 0, 10, 20, ... to 90, 80, 70, ...., respectively, in the text and the ionospheric plots)

Figures 10 and 11 caption: positive flux, negative flux --> positive potential, negative potential

References: Bartels and Veldkamp (1950), Gieseler et al. (2023), Zheng (2013) are listed in the references list, but are not cited in the text. Delete them from the references list, or cite them in the text.