Review of WCD manuscript egusphere-2025-4969 “Storm-Resolving Models Advance Atmospheric Blocking Simulations and Climate Change” by Edgar Dolores-Tesillos et al.

Climate modelling is increasingly moving toward higher spatial resolution, and recent initiatives such as NextGEMS and Climate DT are at the forefront in this development. These projects use kilometre-scale global simulations based on the ICON and IFS modelling systems, producing among the most advanced high-resolution climate model datasets available to the research community at the moment.

As these simulations from Climate DT are becoming more and more available, it is likely that they will play an important role in future climate change assessments due to their ability to better resolve and represent atmospheric key processes such as convection and cyclone structures. Therefore, evaluating the systematic biases of these models is essential. This manuscript contributes to that effort by assessing blocking characteristics in ICON and IFS models. Thus, I believe that this manuscript provides a timely and valuable addition to the literature, and it will be useful for future studies, for example those assessing changes in windstorm frequency or intensity in these high-resolution models.

The authors analyze blocking characteristics and storm tracks from ICON and IFS historical simulations, as well as IFS atmosphere-only (AMIP) simulations, and compare them against ERA5 reanalysis for both northern hemisphere winter and summer seasons. They also compare the results with the CMIP6 ensemble mean. Overall, the study finds that the higher resolution in ICON and IFS models does not necessarily translate to reduced biases in blocking and storm track features. The IFS AMIP simulation, which uses observed sea surface temperatures (SSTs), exhibits the smallest biases, highlighting the importance of realistic SSTs in coupled climate model simulations.

I think the paper was well written, although some sections such as Discussion felt a bit too lengthy. I was also a bit puzzled about the differences between NextGEMS and Climate DT projects and model simulations. As I am by no means an expert on blocking dynamics, I provided only some minor comments related to the presentation and readability of the paper. I hope that the other reviewers can comment more on the methodological choices. Overall, I am happy to recommend publication of this paper after my relatively minor comments have been addressed.

Minor comments:

1. It wasn’t entirely clear for me what the differences are between NextGEMS and Climate DT simulations. Is the IFS FESOM SSP3-7.0 that you analysed the same simulation that will be used also in Climate DT? (it wasn't marked with star in Table 1). In the Supplementary material (Fig. S5-S6) you analysed the ICON NextGEMS and ICON DestinE SSP3-7.0. Is the only difference between them the atmospheric resolution? For example, one clarifying paragraph about the differences between NextGEMS and Climate DT / DestinE could work here. 
2. As far as I know, the Climate DT project also uses the IFS-NEMO model, which has a different ocean component (NEMO model) than in IFS-FESOM. Why didn’t you analyse that model in this paper? It might be worth mentioning why it has been left out. 
3. Throughout the results section, you talk about the North Atlantic and North Pacific basins but it seems that these domains cover the land as well, so they effectively mean the whole hemispheres. For example, Fig. 2a “Blocks in ATL”: does that include the whole hemisphere from -90° to 90°E, and not just the North Atlantic ocean basin?
4. The discussion section is relatively lengthy. It could help readability to divide it into smaller subsections, and maybe condense the text if you find that possible.  
5. Title. When I finished reading the paper, I was honestly a bit disappointed about the models’ skill in reproducing the blocking and storm track features, given the enormous effort put in these digital twin activities. The biases in many variables, especially in SSTs, were very pronounced in IFS and ICON hist runs. Overall, I got the feeling that the new high-resolution models do not appear to outperform the CMIP6 models. In this light, for me, the title “Storm-Resolving Models Advance Atmospheric Blocking Simulations” seems somewhat optimistic.

Line-by-line comments:

L90: What does “energetically consistent climate” mean?

Table 1. Maybe add one column for the years in the periods?

L163: Storm-tracks

Fig. 2 caption: "the extent of the basins is shown as dashed lines." I did not see any dashed lines in Fig. 1. See also minor comment #2 about the basins. Also, the dashed line in Fig. 2 which seems to be the ERA5 median, is missing from the caption. 

L231: Table 4? Same also in L237.

Fig. 3: Is the colorbar value -10 correct? The scale seems otherwise to go with 1 m/s interval. Same for Fig. 8.

Fig. 4: The panels do not have b) but the caption has. Same in Fig. 9.

L276: Maybe add that the northward shift of storm tracks in the Pacific seems to occur in western Pacific only.

L304: What is the Atlantic frequency bias in ICON? I cannot see it from Fig. 6c.

L309: whereas CMIP6 exhibits longer durations. For me, it seems that the duration in CMIP6 in the Pacific (Fig. 7e) is the same as in other models. 

L311: ICON frequency overestimation is true only for high latitudes, but these boxplots (in Fig. 7) show the values for the whole domain, right? So can you actually use that argument as there is underestimation over the lower latitudes in the Pacific (Fig. 6c).

L338: The slightly negative wind bias southwest of Greenland seems to be a very minor feature, and the increased blocking in my opinion is more over southeast of Greenland (Fig. 6a) where the bias in winds is positive (Fig. 8a). But is positive wind bias consistent with increased blocking in the region then? Overall I think the wind biases near Greenland are very consistent between all three models.

L340: Should be maybe Figs. 8b,c

L340: Reduced blocking? I don’t see reduced blocking southeast of Greenland in Fig. 6 in these models. 

L347: The broader jet is present also in the CMIP6 ensemble. Aren’t the CMIP6 jet biases in the Pacific somewhat opposite to that in IFS hist? Fig. 8a vs. 8d?

L369: I think negative SST anomalies are basically everywhere in the North Atlantic in IFS hist so they are not just co-located with positive blocking biases. The interpretation starting from L370 (low SSTs -> favoring high pressure systems) seems to hold only in the high-latitude North Atlantic. The relationship is pretty much the opposite in the Pacific and absent in ICON so I’m not sure how robust the interpretation is. 

L393: Maybe you mean here bias maximum?

Fig. 11 title: Do you mean spatial correlation of blocking biases vs. storm-track biases? The first “biases” was missing which is why I first thought you meant the absolute blocking and not its bias. 

Fig. 11. Is the correlation calculated for ocean-only? 

L435: The reduced blocking in Fig. 12b (JJA) seems to be co-located with the North Atlantic warming hole (Fig. 13d). Thus, I do not really agree with your reasoning about the warmer North Atlantic in this context.

Fig. 13. The colorbar scale in e-f is not symmetric around zero. I would put that symmetric to have balanced view of the biases. 

Figs. S5 and S6. I don't understand these figures. Why does the caption say biases? I thought the b) and c) panels represent the response for climate change (i.e. SSP3–7.0 2020-2049 minus historical)? i.e. similar to Fig. 12a-b but for ICON model. If that's the case, shouldn't the comparison be against the model's historical simulation and not ERA5, given the biases?