the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Opinion: A Critical Evaluation of the Evidence for Aerosol Invigoration of Deep Convection
Adele L. Igel
Hugh Morrison
Wojciech W. Grabowski
Zachary J. Lebo
Abstract. Deep convective updraft invigoration via indirect effects of increased aerosol number concentration on cloud microphysics is frequently cited as a driver of correlations between aerosol and deep convection properties. Here, we critically evaluate the theoretical, modeling, and observational evidence for warm- and cold-phase invigoration pathways. Though warm-phase invigoration is plausible and theoretically supported via lowering of the supersaturation with increased cloud droplet concentration in polluted conditions, the significance of this effect depends on substantial supersaturation changes in real-world convective clouds that have not been observed. Much of the theoretical support for cold-phase invigoration depends on unrealistic assumptions of instantaneous freezing and unloading of condensate in growing, isolated updrafts. When applying more realistic assumptions, impacts on buoyancy from enhanced latent heating via fusion in polluted conditions are largely canceled by greater condensate loading. Foundational observational studies supporting invigoration have several fundamental methodological flaws that render their findings incorrect or highly questionable. Thus, much of the evidence for invigoration has come from numerical modeling, but different models and setups have produced a vast range of results. Furthermore, modeled aerosol impacts on deep convection are rarely tested for robustness, and microphysical biases relative to observations persist, rendering many results unreliable for application to the real world. Without clear theoretical, modeling, or observational support, and given that enervation rather than invigoration may occur for some deep convective regimes and environments, it is entirely possible that the overall impact of cold-phase invigoration is negligible. Substantial mesoscale variability of dominant thermodynamic controls on convective updraft strength coupled with substantial updraft and aerosol variability in any given event are poorly quantified by observations and present further challenges to isolating aerosol effects. Observational isolation and quantification of convective invigoration by aerosols is also complicated by limitations of available cloud condensation nuclei and updraft speed proxies, aerosol correlations with meteorological conditions, and cloud impacts on aerosols. Furthermore, many cloud processes such as entrainment and condensate fallout modulate updraft strength and aerosol-cloud interactions, varying with cloud life cycle and organization, but these processes remain poorly characterized. Considering these challenges, recommendations for future observational and modeling research related to aerosol invigoration of deep convection are provided.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3939 KB) - Metadata XML
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- Final revised paper
Journal article(s) based on this preprint
Adam C. Varble et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-938', Anonymous Referee #1, 30 May 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-938/egusphere-2023-938-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2023-938', Anonymous Referee #2, 01 Jul 2023
General Comment: This opinion article summarizes the complexities of assessing the microphysical impacts of aerosol particles on clouds, both from modeling and observational perspectives. Overall, the article was well-written and nicely demonstrates many of the uncertainties associated with answering the question on whether cloud condensation nuclei concentrations strengthen convective cloud vertical motions. I provided some comments below that I think would make the manuscript clearer, as well as a few important points and citations that I think the authors have missed.
Specific Comments:
Title: How do the authors define deep convection? Since one of the two mechanisms that the authors are focusing on is the warm-phase mechanism, perhaps the title should be invigoration of “Convective Clouds” instead of “Deep Convection?”
L34: The authors initially state that “There are many proposed effects of aerosol on deep convection,” and then subsequently focus the remainder of the manuscript on how cloud condensation nuclei may impact hydrometeor production and related microphysical impacts. While the authors do state on L63 that this paper will focus how aerosol will impact latent heating, it would perhaps be useful to make very clear somewhere in these initial stages of the manuscript that the following topics are not discussed, even though they could also impact this invigoration question: 1) aerosol radiative effects and 2) that aerosol can act as ice nucleating particles, which can also impact the microphysics within clouds. To be clear, I do not think the authors should go into much detail on these other topics as they themselves are complex, but rather mention them as additional factors to this problem.
L100: Marinescu et al., 2021 also shows many models with negative impacts on updrafts in the cold-phase regions (above 7km AGL) with the ensemble median having no response to aerosol in this region and should be included here as well.
L170: One of the primary findings of Marinescu et al., 2021 is that the consistent warm phase invigoration in 7 different models is likely attributed to increased environmental instability due to aerosol-induced boundary layer changes and can be included here as another example.
L230-232: Many additional studies have shown an assessment of updraft changes under different environmental conditions, so I think the citation list on L232 should have an e.g. in front of it. Some additional examples of the early research on this, as well as some more recent work are Fan et al., 2007; Lee et al., 2008; Storer et al., 2010; and Sokolowsky et al., 2022, but there are many others as well.
L234-238: I found this statement a little confusing, and perhaps the readership would benefit from a clearer explanation here. Specifically, how can an environment “adjust to aerosol-induced convective invigoration”?
L265. There have been community-wide model intercomparison studies to assess aerosol effects on clouds, with several more currently on-going. These model intercomparison projects have even focused on topics such as CCN invigoration of updrafts (Marinescu et al., 2021). I think these community-wide efforts should be highlighted here, as they also represent an ensemble of results and a way to understand variability in modeling results.
L277: Were “substantial biases” in model simulations discussed? Perhaps consider removing “biases” here or mention what these biases are, with references?
L374-376: “The failure of this approach results from mixing cloud and meteorological regimes together …" Are the authors stating that the issue is that regimes need to be further constrained by both cloud types AND meteorological regime? I found this statement a little confusing.
L915: Should arrow “color” be arrow “direction?”
References:
Fan, J., R. Zhang, G. Li, and W. K. Tao, 2007: Effects of aerosols and relative humidity on cumulus clouds. J. Geophys. Res., 112, D14204, https://doi.org/10.1029/2006JD008136.
Lee, S. S., L. J. Donner, V. T. J. Phillips, and Y. Ming, 2008: The dependence of aerosol effects on clouds and precipitation on cloud-system organization, shear and stability. J. Geophys. Res., 113, D16202, https://doi.org/10.1029/2007JD009224.
Marinescu, P. J., and Coauthors, 2021: Impacts of Varying Concentrations of Cloud Condensation Nuclei on Deep Convective Cloud Updrafts—A Multimodel Assessment. J. Atmos. Sci., 78, 1147–1172, https://doi.org/10.1175/JAS-D-20-0200.1.
Sokolowsky, G. A., S. W. Freeman, and S. C. van den Heever, 2022: Sensitivities of Maritime Tropical Trimodal Convection to Aerosols and Boundary Layer Static Stability. J. Atmos. Sci., 79, 2549–2570, https://doi.org/10.1175/JAS-D-21-0260.1.
Storer, R. L., S. C. van den Heever, and G. L. Stephens, 2010: Modeling aerosol impacts on convective storms in different environments. J. Atmos. Sci., 67, 3904–3915, https://doi.org/10.1175/2010JAS3363.1.
Citation: https://doi.org/10.5194/egusphere-2023-938-RC2 -
AC1: 'Response to reviewers', Adam Varble, 25 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-938/egusphere-2023-938-AC1-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-938', Anonymous Referee #1, 30 May 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-938/egusphere-2023-938-RC1-supplement.pdf
-
RC2: 'Comment on egusphere-2023-938', Anonymous Referee #2, 01 Jul 2023
General Comment: This opinion article summarizes the complexities of assessing the microphysical impacts of aerosol particles on clouds, both from modeling and observational perspectives. Overall, the article was well-written and nicely demonstrates many of the uncertainties associated with answering the question on whether cloud condensation nuclei concentrations strengthen convective cloud vertical motions. I provided some comments below that I think would make the manuscript clearer, as well as a few important points and citations that I think the authors have missed.
Specific Comments:
Title: How do the authors define deep convection? Since one of the two mechanisms that the authors are focusing on is the warm-phase mechanism, perhaps the title should be invigoration of “Convective Clouds” instead of “Deep Convection?”
L34: The authors initially state that “There are many proposed effects of aerosol on deep convection,” and then subsequently focus the remainder of the manuscript on how cloud condensation nuclei may impact hydrometeor production and related microphysical impacts. While the authors do state on L63 that this paper will focus how aerosol will impact latent heating, it would perhaps be useful to make very clear somewhere in these initial stages of the manuscript that the following topics are not discussed, even though they could also impact this invigoration question: 1) aerosol radiative effects and 2) that aerosol can act as ice nucleating particles, which can also impact the microphysics within clouds. To be clear, I do not think the authors should go into much detail on these other topics as they themselves are complex, but rather mention them as additional factors to this problem.
L100: Marinescu et al., 2021 also shows many models with negative impacts on updrafts in the cold-phase regions (above 7km AGL) with the ensemble median having no response to aerosol in this region and should be included here as well.
L170: One of the primary findings of Marinescu et al., 2021 is that the consistent warm phase invigoration in 7 different models is likely attributed to increased environmental instability due to aerosol-induced boundary layer changes and can be included here as another example.
L230-232: Many additional studies have shown an assessment of updraft changes under different environmental conditions, so I think the citation list on L232 should have an e.g. in front of it. Some additional examples of the early research on this, as well as some more recent work are Fan et al., 2007; Lee et al., 2008; Storer et al., 2010; and Sokolowsky et al., 2022, but there are many others as well.
L234-238: I found this statement a little confusing, and perhaps the readership would benefit from a clearer explanation here. Specifically, how can an environment “adjust to aerosol-induced convective invigoration”?
L265. There have been community-wide model intercomparison studies to assess aerosol effects on clouds, with several more currently on-going. These model intercomparison projects have even focused on topics such as CCN invigoration of updrafts (Marinescu et al., 2021). I think these community-wide efforts should be highlighted here, as they also represent an ensemble of results and a way to understand variability in modeling results.
L277: Were “substantial biases” in model simulations discussed? Perhaps consider removing “biases” here or mention what these biases are, with references?
L374-376: “The failure of this approach results from mixing cloud and meteorological regimes together …" Are the authors stating that the issue is that regimes need to be further constrained by both cloud types AND meteorological regime? I found this statement a little confusing.
L915: Should arrow “color” be arrow “direction?”
References:
Fan, J., R. Zhang, G. Li, and W. K. Tao, 2007: Effects of aerosols and relative humidity on cumulus clouds. J. Geophys. Res., 112, D14204, https://doi.org/10.1029/2006JD008136.
Lee, S. S., L. J. Donner, V. T. J. Phillips, and Y. Ming, 2008: The dependence of aerosol effects on clouds and precipitation on cloud-system organization, shear and stability. J. Geophys. Res., 113, D16202, https://doi.org/10.1029/2007JD009224.
Marinescu, P. J., and Coauthors, 2021: Impacts of Varying Concentrations of Cloud Condensation Nuclei on Deep Convective Cloud Updrafts—A Multimodel Assessment. J. Atmos. Sci., 78, 1147–1172, https://doi.org/10.1175/JAS-D-20-0200.1.
Sokolowsky, G. A., S. W. Freeman, and S. C. van den Heever, 2022: Sensitivities of Maritime Tropical Trimodal Convection to Aerosols and Boundary Layer Static Stability. J. Atmos. Sci., 79, 2549–2570, https://doi.org/10.1175/JAS-D-21-0260.1.
Storer, R. L., S. C. van den Heever, and G. L. Stephens, 2010: Modeling aerosol impacts on convective storms in different environments. J. Atmos. Sci., 67, 3904–3915, https://doi.org/10.1175/2010JAS3363.1.
Citation: https://doi.org/10.5194/egusphere-2023-938-RC2 -
AC1: 'Response to reviewers', Adam Varble, 25 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-938/egusphere-2023-938-AC1-supplement.pdf
Peer review completion
Journal article(s) based on this preprint
Adam C. Varble et al.
Adam C. Varble et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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