the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Jun 2025
The role of aerosols and meteorological conditions in shaping cloud droplet development in New Mexico summer deep-convective systems
Abstract. The accurate representation of aerosol physicochemical properties is important when describing aerosol-cloud interactions. The Deep Convective Microphysics Experiment (DCMEX) aimed to improve the representation of microphysical processes in deep convective systems. As part of this project, an airborne campaign (July to August 2022) was conducted to characterize the thermodynamics-dynamic-aerosol-cloud system over the isolated Magdalena Mountains in New Mexico, US. Backward dispersion analyses identified a transition in dominant airmass origins from Northwest (NW) continental to Southeast (SE) aged oceanic flow, coinciding with substantial changes in meteorological conditions and aerosol characteristics. The SE-flow period generally exhibited lower lifting condensation levels, enhanced convection, higher boundary layer humidity, and more frequent and intense precipitation, compared to the NW-flow period. During the SE-flow period, aerosol size distributions showed a more pronounced bimodality, characterized by increased Aitken-mode concentrations and fewer but larger accumulation-mode particles, indicating enhanced cloud processing. Submicron aerosols exhibited larger sulfate fractions, more oxidized organics, and greater hygroscopicity. Correspondingly, clouds presented larger droplet sizes and liquid water contents. A bin-microphysics parcel model was also employed to simulate the development of cloud droplets, constrained by airborne observations. Model-observation comparisons highlight the critical role of aerosol entrainment in reproducing the observed broad cloud droplet spectra extending toward small sizes. The results underscore the combined influence of meteorological conditions and aerosol characteristics on cloud microphysics under different flow regimes and emphasize the importance of aerosol entrainment in the development of deep convective clouds. This study provides valuable constraints for improving parameterizations of aerosol-cloud interactions in convective systems.
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RC1: 'Comment on egusphere-2025-2600', Anonymous Referee #1, 14 Jul 2025
This study beautifully documents the deep convective clouds that occur almost daily during summer over the Magdalena Mountains, which serve as a natural laboratory for continental convection. I enjoyed reading the detailed descriptions, which provide a comprehensive account and interpretation of the observations surrounding and within these clouds.
The study describes the differences and probable causes of the aerosols, thermodynamics, and composition of the clouds under different air mass origins. These clouds, unsurprisingly, have high and cold bases, microphysically highly continental, with little or no significant warm rain processes. It follows that the clouds remain supercooled at least up to the -20 °C isotherm, which was the top of the measured flight levels. Apparently, only growing cloud towers were penetrated, because maturing clouds do glaciate at least occasionally at these high supercooled temperatures as they mature. So, please clarify the selection criteria for cloud penetrations.
The most enlightening part of the paper was the comparison of the clouds' vertical microphysical profiles with the parcel model, considering various assumptions. It showed the potential role of mixing in cloud drop activation and evaporation aloft.
While informative, the paper lacks a scientific focus and a statement of novelty, i.e., where does it contribute fundamental understanding to the state of the art? This is evident in the fact that much of the introduction is devoted to issues not addressed by the findings of this study, such as the extensive description of the aerosol convective invigoration hypothesis.
This shortcoming can be overcome by focusing on the processes of cloud mixing (homogeneous vs. inhomogeneous) and the additional activation of drops versus evaporation aloft. To do that, I suggest:
- Replace much of the irrelevant parts of the introduction with a review of the known background on the processes that cause deviations from adiabatic parcels in deep non-precipitating water clouds.
- Review causes for shaping the cloud drop size distributions with height in such clouds.
- In the parcel simulations, provide the exact handling, formulation, and fraction of mixing with ambient air and secondary aerosol activation. Which extent of mixing would provide the best match with observations? Would replacing the aerosol size distribution near cloud base with its vertical profile improve the agreement between the simulated and observed cloud microstructure vertical profile?
- Provide the formulation of the mix between homogeneous and inhomogeneous mixing, and which fractionation provides the best match to observations.
There is a wealth of data from the individual flights, warranting an additional study that focuses on this, aiming to find the parameterization that best fits the individual flights. It is likely beyond the scope of this paper, but at the very least, state that this is a potential future study when addressing the most general questions above.
Minor comments:
Line 395: It is much more likely that the SO2 sources at the southeast are from urban and industrial emissions, including the extensive oil fields and refineries.
Line 500: Replace “raindrops” with “cloud drops”.
Line 522: All cloud drop size distributions had a local maximum concentration at 6.5 μm and a local minimum at 8 μm. It appears to be a problem of incorrect bin widths for the CDP, rather than a bimodal drop size distribution being the issue.
Line 555 and the whole paragraph: How was the mixing performed in the model?
And how was the portion of homogeneous and inhomogeneous mixing determined?
Lines 613-614: The added precipitation with warmer bases can be explained by the increased water vapor content and the corresponding additional condensation. Please add this as a further possible explanation.
Fig. S1: Please state the heights of the origins of the back tracks.
Citation: https://doi.org/10.5194/egusphere-2025-2600-RC1 -
RC2: 'Comment on egusphere-2025-2600', Anonymous Referee #2, 06 Aug 2025
Review of “The role of aerosols and meteorological conditions in shaping cloud droplet development in New Mexico summer deep-convective systems” by Huihui Wu et al.
Major Comments
This manuscript deals with the relationship between aerosols, meteorological conditions and the development of cloud droplets and their size distribution. The methodology is based on both aircraft observations and numerical parcel model with bin microphysics. The overall goal is to understand the role of aerosols (number and type), constrained by meteorology, on the droplet formation mechanisms. The authors argue that aerosol entrainment is an important mechanism to explain the broadening of the droplet spectra.
Overall, I think the manuscript is deserving of publication, but there are some major and minor adjustments to be made. I will point some major comments here and list a few minor comments later.
1) There is a disconnect between what the manuscript seems to be by reading the title, abstract and introduction and what the manuscript actually is. When I started to read the manuscript I thought it was going to be about the invigoration hypothesis, which is extensively reviewed in the introduction. However, the results section dedicates a lot of text to the description of the aerosol properties and air mass backtrajectories. While interesting, it doesn’t seem to fit what the I expected from the title/abstract/introduction. The same could be said about the entrainment process, which seems to be a major focus of the study and is not mentioned in the title, for instance. I will give my suggestions together with my second comment below.
2) The origin of the issue listed above is possibly related to the many foci present in the manuscript:
I) There is discussion about air masses/backtrajectories
II) There is discussion on physicochemical properties of aerosols, with vertical profiles
III) Only then the manuscript goes into the discussion that I was expecting to see from the start, which is the droplet spectra properties
IV) Compounding the many-foci issue, there is also a lot to cover from the observations side as well as from the modeling side. Therefore, there is also multiple foci on the methodology side.
With the given above, the manuscript ended up being, in my opinion, too long and without a clear message. I would suggest the authors to rewrite the manuscript in a way to make their contribution more explicit. From reading the manuscript, I think the most interesting aspect was the comparison between the observations and the bin model with the entrainment discussion. Because the manuscript had so many foci, this discussion ended up being shorter and shallower than expected. For instance, the authors mention that the entrainment effect is important to reproduce the observed droplet spectra width. However, there is no figure showing this parameter explicitly. There is plenty of literature about the aerosol effect on droplet width, which could be used as context to the present study.
To summarize and provide a more objective suggestion:
I would suggest to refocus the title/abstract/introduction towards this entrainment effect and the observation-model comparison. The aerosol/backtrajectories analysis, while interesting, could be left out without hurting the overall message of the manuscript. This part could be later incorporated in a new submission focused on the aerosol discussion, in my opinion.
Minor Comments
Lines 40-43: no references are given. Please provide appropriate references.
Lines 44-45: there are more references to add here, most notably the IPCC reports
Lines 54-55: again, no references given about the aerosol effect on cloud cover, lifetime, etc
Line 89: would by nice to mention which advances in measurement techniques
Line 111 and Line 114: please avoid using “etc”
Line 178: cloud development → cloud parcel development ? (since it is a cloud parcel model)
Line 210: remains → retains?
Lines 292-294: no need to repeat the “(0.1 to 3 micron)” parenthesis, since Na and Nsa were already defined earlier
Line 310: please consider citing “Isoprene nitrates drive new particle formation in Amazon’s upper troposphere” by Curtius et al. (2024). It is a recent and relevant paper on the subject, available in Nature: https://www.nature.com/articles/s41586-024-08192-4. Also note that the aerosol-rich layer in the Amazonian upper troposphere is mostly above 8 km, which seems to be the upper limit in your study.
Figure 7 (and others): there should be legends in the figures themselves to explain what the different lines are. The figures should be as self-sufficient as possible, without needed to read the caption.
Citation: https://doi.org/10.5194/egusphere-2025-2600-RC2
Data sets
DCMEX: Collection of in-situ airborne observations, ground-based meteorological and aerosol measurements and cloud imagery for the Deep Convective Microphysics Experiment Facility for Airborne Atmospheric Measurements; D. Finney et al. https://catalogue.ceda.ac.uk/uuid/b1211ad185e24b488d41dd98f957506c/
Model code and software
bin-microphysics-model Paul Connolly https://github.com/UoM-maul1609/bin-microphysics-model
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