Updraft Dynamics and Microphysics: On the Added Value of the Cumulus Thermal Reference Frame in Simulations of Aerosol–Deep Convection Interactions
One fundamental question about atmospheric moist convection processes that remains debated is whether or under what conditions a relevant variability in background aerosol concentrations may have a significant dynamical impact on convective clouds and their associated precipitation. Furthermore, cur...
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Published in: | Atmospheric chemistry and physics 2022-01, Vol.22 (2), p.711-724 |
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Main Authors: | , , |
Format: | Article |
Language: | eng |
Subjects: | |
Online Access: | Get full text |
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Summary: | One fundamental question about atmospheric moist convection processes that remains debated is whether or under
what conditions a relevant variability in background aerosol concentrations may have a significant dynamical impact on convective
clouds and their associated precipitation. Furthermore, current climate models must parameterize both the microphysical
and the cumulus convection processes, but this is usually implemented separately, whereas in nature there is a strong coupling
between them. As a first step to improve our understanding of these two problems, we investigate how aerosol concentrations
modify key properties of updrafts in eight large-eddy permitting regional simulations of a case study of scattered convection
over Houston, Texas, in which convection is explicitly simulated and microphysical processes are parameterized. Dynamical
and liquid-phase microphysical responses are investigated using two different reference frames: static cloudy-updraft grid
cells versus tracked cumulus thermals. In both frameworks we observe the expected microphysical responses to higher aerosol
concentrations, such as higher cloud number concentrations and lower rain number concentrations. In terms of the dynamical
responses, both frameworks indicate weak impacts of varying aerosol concentrations relative to the noise between simulations
over the observationally derived range of aerosol variability for this case study. On the other hand, results suggest that thermals
are more selective than cloudy-updraft grid cells in terms of sampling the most active convective air masses. For instance,
vertical velocity from thermals is significantly higher at upper levels than when sampled from cloudy-updraft grid points,
and several microphysical variables have higher average values in the cumulus thermal framework than in the cloudy-updraft
framework. In addition, the thermal analysis is seen to add rich quantitative information about the rates and covariability of
microphysical processes spatially and throughout tracked thermal lifecycles, which can serve as a stronger foundation for
improving subgrid-scale parameterizations. |
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ISSN: | 1680-7316 1680-7324 1680-7324 |