General comments

This manuscript presents an extensive and well-documented experimental database on downburst-like flows generated using buoyancy-driven and mechanically-assisted impinging jets in a large-scale thermal wind tunnel. The CLIMATHUNDERR project addresses an important, relevant and timely topic: the experimental replication of non-stationary thunderstorm downbursts under realistic thermodynamic conditions. The Authors propose a compelling contribution, succeeding in bridging a methodological gap between traditional gravity current and impinging jet techniques by reproducing buoyancy effects at large scales using only air as the working fluid. This work constitutes a notable advancement, and will influence the literature on this topic in the following years.

The experimental campaign is impressively ambitious,  being definitely out of the current state-of-the-art. At the same time, the gathered database seems comprehensive. It combines advanced measurement techniques (large-scale PIV, distributed thermocouples), caused by a systematic variation of governing parameters (such as the variation of temperature, piston speed). It also includes the study of the problem on real-world orography. The processed datasets via Zenodo under open-access licensing will significantly enhances the paper’s value for the community.

The manuscript is well-organized, clearly written, and follows a logical structure. The physical modeling choices, instrumentation, and experimental design are well justified. 

However, some aspects would benefit from further clarification and elaboration, and I will be pointing them in the following. In fact, clarifying them will help contextualize the scope and limitations of the dataset for future users. In particular, these will concern the scaling of the experiments with respect to real-world phenomena, as well as the uncertainties in the data estimation.

Overall, the manuscript makes a valuable contribution to the wind engineering and atmospheric science communities. It meets the ESSD criteria for scientific quality, transparency, and data reusability. I recommend its acceptance after minor revisions, as outlined below.

Specific Comments

Section 3.3: several quantities withing Eqs. (1) and (2) are not introduced, unless I am mistaken. w_B may be immediately introduced as the expected vertical buoyant jet velocities, avoiding detailing that w is the vertical velocity of the jet; concerning z, it is not specified whether it is pointing upwards or downwards, if I am not mistaken. The terms “t” is not introduced, and neither are the nomenclatures “d/dt”, or the partial derivatives. Analogously, also several terms in Eq. (2) are not introduced. Besides, I would like to ask the Authors whether the hypothesis of non-varying reference density value could be verified.

Section 3.3: On the Richardson number, do the Authors think there is a variability in its estimation for full-scale downbursts? They refer to a specific case, but I am wondering whether it could vary across several full-scale records. Besides, I am wondering whether there is variability in the estimation of the Richardson number even in the experiments. Could the Authors provide more details about its variability with the other parameters of the tests ? I think it would make a very interesting point of the discussion.

Eq (5): It seems to me the Authors tried to estimate w_IJ based on the flow rate conservation. Could this be instrumental to identify w_GC (something that was discussed at Lines 244/245).

Line 274: could the Authors provide details on how they synchronized all the different measurements based on the louvers’ opening ?  

Section 3.4.1: Do the simulated experimental phenomena “resemble” any of the full-scale events present in the database of the University of Genoa ? Specifically, the relative position of the orography model is allowing a touchdown point that may recall any full-scale event ? I believe comparison of wind velocity time-histories in specific points (i.e., anemometric stations in Genoa) will be a great point for future studies.

Do the Authors expect any end-effects induced by the boundary of the orography model that may cause some impact on the experimental measurements ? I am thinking how the orography model was installed within the surrounding environment in the laboratory. Was it flushing? I could not understand this piece of information from the manuscript. Perhaps an additional close-up picture would be beneficial.

Section 3,5 and in general: How do the Authors handle measurement uncertainties of the relevant instrumentation ? Which is the impact that the tolerance of the instrumentation may have on the results ? I am thinking, for example, to the different parameters included in Table 2 for the same “nominal” experiment. Could measurement uncertainty be important in this discrepancy? Still on this topic, the Authors note (p. 18–19) that the exact reproduction of experimental conditions (e.g., ∆T, piston speed) was challenging, and that each test is to be considered "unique." While this is understandable, some discussion is needed on how such variability might affect data interpretation, particularly in cross-test comparisons or model training/validation. Are users encouraged to use specific test subsets (e.g., most stable ∆T cases)?

Line 463- 466: as mentioned in the caption, the lines in Figure 9c is not a temperature timeseries, but it is the time-history of the percentage variation estimated from the thermocouples. I think this should be reflected in Line 465, replacing the terms “temperature timeseries” accordingly. This would also allow the Authors to modify the caption of Figure 9, avoiding the part  “Temperature is actually the percentage …”. 

Still on this Figure, I do not understand where are the surface thermocouples in Fig 9a-9b; could the Authors make them clearer ? Finally, I think that the legend voice “5.50 s” in Figure 9c may be replaced with “5.50 s + 0.5s”. 

The paper meets the general principles of open data, but it would benefit from a brief discussion of metadata structure, variable names, and standard formats used. Are NetCDF, CSV, or other structured formats adopted? Is the dataset interoperable with common post-processing tools?

As final general conclusions, also to help with the next perspectives:

It is well-known the significant effects played by the Reynolds number in numerous aspects related to Fluid Mechanics and aerodynamics of bluff-bodies, which affect the design of wind tunnel studies of structures for Wind Engineering purpose. I am wondering if the Authors expect analogous effects in this study concerning thermal aspects because of significant scaling effects studied here (1:2000 scale). I think it would be an interesting aspect to deepen in future studies.

Still related to this aspect: In the introduction, it was mentioned that the models by Xhelaj et al. (2020, 2022, 2024) will be enhanced by incorporating the results from the current experiments to account for the thermal effects on downburst wind evolution. May I ask the Authors to detail how do they plan on doing that, also in light of scaling considerations ? What do they expect ?

Technical comments

Line 246: is the term “wGC=” needed within the parenthesis, or “wB” should suffice ?

Line 259: I think there is a missing “m” after ground level( 0.10 … below the nozzle).

Bibliography

The adopted bibliography is adequate; however, I note the following potential issues:

Some journals are cited with their full name (e.g., Journal of Wind Engineering and Industrial Aerodynamics), others are cited with abbreviations. Concerning the latter, there are some that are cited with a final dot (e.g., Mon. Wea. Rev.) and others without it (e.g., Environ Fluid Mech). I suggest the Authors to be consistent throughout, following ESSD's guidelines. 

Canepa et al. (2025) is not in the bibliography; could the Authors add it ?

In the text, it is always mentioned Canepa (2024), but in actuality in the bibliography there are two (a and b); I suggest the Authors to modify the text accordingly.

The authors describe a novel downburst experiment data set can be used for various types of studies, with particular interest for engineers.

The experimental data are valuable in that the experiments are the first to combine both of the widely used techniques for recreating downbursts – gravity current and impinging jet. However, the degree to which this is done successfully is difficult to determine, particularly since – as the authors say – each experiment in this study must be regarded as unique.

The organization of the paper and the writing are adequate, though there are some minor problems.

Overall, the authors do not adequately explain how downbursts develop and their observed spatial extent (in fact, what they do describe is incorrect). The authors also make reference to several types of vortices associated with downbursts but do not adequately describe these until late in the paper, and even then do not provide evidence that they exist in nature. This does not inspire confidence in the data or limited results that are presented.

The paper can, however, likely be improved with a number of minor revisions. Recommendations are described in the detailed comments below.

Detailed Comments

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L14 – The abstract beings by discussing downbursts but on this line switches to the formation of thunderstorms. It took me a few reads to understand that “warm, humid air is lifted” does not refer to lifting by the horizontal outflow of a downburst. This needs to be revised to improve clarity for the reader.

L16 – This is the only line in the entire paper that tries to describe the origins of a downburst, and does so poorly. It should say that the air parcels sink due to ‘negative buoyancy’. And it should be made clear – perhaps not in the abstract but at least in the introduction of the paper – that the negative buoyancy does not just happen on its own, that it requires evaporative cooling of precipitation.

L17 – Re a ‘symmetrical vortex’, the authors should be clear about what that means i.e. symmetrical about what? And there isn’t a need for an acronym e.g. ‘PV’ if that term is not used again in the abstract.

L45 – Re ‘non-stationary winds’, how can wind be non-stationary? Do the authors mean ‘non-stationary wind phenomena’, where the phenomena are non-stationary?

L46-47 – I don’t believe that an increase in the frequency or intensity of such events has been shown, only projected. The authors need to revise this sentence to reflect that.

L57 – The authors state the downbursts have a limited spatial extent of only a few km. That is incorrect. Downbursts can be tens of km across. If downbursts are 4 km or less, they are referred to as ‘microbursts’. See Fujita (1981). If the authors are intending to investigate microbursts, and not downbursts in general, they should say so.

L67 – Should be ‘combined with thermal effects’

L72 – Should be ‘a downburst develops’

L72 – Yes, a downburst is associated with relatively cold, dense air descending from aloft, but:

• Needs to mention how i.e. evaporative cooling of precipitation
• Needs to mention that it can be enhanced by precipitation loading
• Needs to mention that ‘dry downbursts’ can occur in the absence of a thunderstorm, and how that can happen

L93 – CAPE is not measured at the ground, it is measured through much of the depth of the troposphere. I’m sure at least some of the authors know this, so it’s disappointing to see this here. It of course needs to be corrected.

L107 – The term ‘wind-safer’ is not valid; the authors need to find another way to express this.

L117 – What is the difference between ‘meteorological’ and ‘anemometric’ measurements? I think just meteorological measurements would suffice here.

L119-120 – I think the Mediterranean Seas serving a source of warn and humid air for thunderstorm updrafts is an assumption made by the authors. If not, please provide references.

Figure 1 – There is a dotted white line on the upper plenum – is there supposed to be a vertical measurement shown here?

Figure 1 – The yellow arrow appears to show only one orientation, so not sure why ‘upstream/downstream orientations’ is mentioned in the caption.

L177 – ‘in the view of ensuring’ should be ‘in order to ensure’

L190 – Is the sheet really only 0.03 mm thick? Just want to make sure this isn’t a typo.

L192 – The authors mention a primary vortex, a secondary vortex, and trailing vortices, but these are not described in detail and for the latter two the origins are not explained. There needs to be a paragraph or two at this point in the manuscript that describes these and refers to a idealized schematic that shows all of the vortices occurring at once (based on Fig 8c). Showing what these vortices are so late in the paper (Fig. 8) is not adequate. The authors also need to be state whether the SV and TV have ever actually been observed to occur.

L222 – Not sure if ‘an overpressure’ is an actual engineering term – if not, please revise.

L311 – Again, the PV and SV need to be explained earlier with reference to an idealized schematic.

L317 – ‘allows to extend’ should be ‘allows for’

Figure 4. Spectacular results here. The caption mentions ‘vortices’ but should say whether they are PV, SV or TV or some combination.

Figure 4. The labels on the axis for b are too small to be legible. Need to increase the font size.

Figure 5. Caption should say what the arrows and the broken line mean and that the green rectangle represents the PIV field of view.

L350 – Should be ‘0.5 mm’ and ‘300 mm’

Figure 6. In caption, ‘model’ should be ‘orography model’ for clarity.

L391 - ‘model’ should be ‘orography model’ here for clarity

L432 – Re ‘1000 ms’, why not just write ‘1 s’?

Figs 8 and 9 – It’s difficult to make out the axis titles – please correct.

Figure 9. Re ‘Temperature is actually’, should probably say ‘the y-axis is’ – it’s not temperature.

L483 – Where would these ‘full-scale recordings of downburst events’ come from? The authors should expand on this in the text.

References – a paper on downbursts that does not reference Fujita – who discovered downbursts – is incomplete.

Reference

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Fujita, 1981: Tornadoes and downbursts in the context of generalized planetary scales. J. Atmos. Sci., 38, 1511-1534.