Uncertainty from the choice of microphysics scheme in convection-permitting models significantly exceeds aerosol effects
This study investigates the hydrometeor development and response to cloud droplet number concentration (CDNC) perturbations in convection-permitting model configurations. We present results from a real-data simulation of deep convection in the Congo basin, an idealised supercell case, and a warm...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-10-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/17/12145/2017/acp-17-12145-2017.pdf |
Summary: | This study investigates the hydrometeor development and response to
cloud droplet number concentration (CDNC) perturbations in
convection-permitting model configurations. We present results from
a real-data simulation of deep convection in the Congo basin, an
idealised supercell case, and a warm-rain large-eddy simulation
(LES). In each case we compare two frequently used double-moment bulk
microphysics schemes and investigate the response to CDNC
perturbations. We find that the variability among the two schemes,
including the response to aerosol, differs widely between these
cases. In all cases, differences in the simulated cloud morphology and
precipitation are found to be significantly greater between the
microphysics schemes than due to CDNC perturbations within each
scheme. Further, we show that the response of the hydrometeors to CDNC
perturbations differs strongly not only between microphysics schemes,
but the inter-scheme variability also differs between cases of
convection. Sensitivity tests show that the representation of
autoconversion is the dominant factor that drives differences in rain
production between the microphysics schemes in the idealised
precipitating shallow cumulus case and in a subregion of the Congo
basin simulations dominated by liquid-phase processes. In this region,
rain mass is also shown to be relatively insensitive to the radiative
effects of an overlying layer of ice-phase cloud. The conversion of
cloud ice to snow is the process responsible for differences in cold
cloud bias between the schemes in the Congo. In the idealised
supercell case, thermodynamic impacts on the storm system using
different microphysics parameterisations can equal those due to
aerosol effects. These results highlight the large uncertainty in
cloud and precipitation responses to aerosol in convection-permitting
simulations and have important implications not only for process
studies of aerosol–convection interaction, but also for global
modelling studies of aerosol indirect effects. These results indicate
the continuing need for tighter observational constraints of cloud
processes and response to aerosol in a range of meteorological
regimes. |
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ISSN: | 1680-7316 1680-7324 |