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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. Many 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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Type‐Dependent Impact of Aerosols on Precipitation Associated With Deep Convective Cloud Over East Asia
Abstract Aerosol‐cloud‐precipitation interactions represent one of the most significant uncertainties in climate simulation and projection. In particular, the impact of aerosols on precipitation is highly uncertain due to limited and conflicting observational evidence. A major challenge is to distinguish the effects of different types of aerosols on precipitation associated with deep convective clouds, which produces most of the precipitation in East Asia. Here, we use 9‐yr observations from multiple satellite‐borne sensors and find that the occurrent frequency of heavy rain increases while that of light rain decreases with the increase of aerosol optical depth (AOD) for dust and polluted continental aerosol types. For average hourly precipitation amount, elevated smoke tends to suppress deep convective precipitation, while dust and polluted continental aerosols enhance precipitation mainly through the invigoration of deep convection. The invigoration effect is more significant for clouds with higher cloud base temperature (CBT), while no significant invigoration is observed when CBT is <12°C. A great contrast is found for the response of average hourly precipitation amount to aerosols over ocean and land. While the prevailing continental aerosol types other than smoke increase precipitation, the marine aerosols first enhance and then inhibit precipitation with the increase of AOD. Moreover, our analysis indicates that the above‐mentioned enhancement and inhibition effects on precipitation are mainly caused by aerosols themselves, rather than by the covariation of meteorological factors. These observed relationships between different aerosol types and precipitation frequency and amount provide valuable constraints on the model forecasting of precipitation.
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- Award ID(s):
- 2103820
- PAR ID:
- 10374541
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 127
- Issue:
- 2
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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