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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Status: open (until 05 Aug 2025)
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RC1: 'Comment on egusphere-2025-2600', Anonymous Referee #1, 14 Jul 2025
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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
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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