Influences of an entrainment–mixing parameterization on numerical simulations of cumulus and stratocumulus clouds
<p>Different entrainment–mixing processes can occur in clouds; however, a homogeneous mixing mechanism is often implicitly assumed in most commonly used microphysics schemes. Here, we first present a new entrainment–mixing parameterization that uses the grid mean relative humidity without requ...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/5459/2022/acp-22-5459-2022.pdf |
| Summary: | <p>Different entrainment–mixing processes can occur in clouds; however, a homogeneous mixing mechanism is often implicitly assumed in most commonly used microphysics schemes. Here, we first present a new entrainment–mixing parameterization that uses the grid mean relative humidity without requiring
the relative humidity of the entrained air. Then, the parameterization is
implemented in a microphysics scheme in a large eddy simulation model, and
sensitivity experiments are conducted to compare the new parameterization
with the default homogeneous entrainment–mixing parameterization. The
results indicate that the new entrainment–mixing parameterization has a
larger impact on the number concentration, volume mean radius, and cloud
optical depth in the stratocumulus case than in the cumulus case. This is
because inhomogeneous and homogeneous mixing mechanisms dominate in the
stratocumulus and cumulus cases, respectively, which is mainly due to the
larger turbulence dissipation rate in the cumulus case. Because
stratocumulus clouds break up during the dissipation stage to form cumulus
clouds, the effects of this new entrainment–mixing parameterization during
the stratocumulus dissipation stage are between those during the
stratocumulus mature stage and the cumulus case. A large aerosol
concentration can enhance the effects of this new entrainment–mixing
parameterization by decreasing the cloud droplet size and evaporation timescale. The results of this new entrainment–mixing parameterization with
grid mean relative humidity are validated by the use of a different
entrainment–mixing parameterization that uses parameterized entrained air
properties. This study sheds new light on the improvement of
entrainment–mixing parameterizations in models.</p> |
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| ISSN: | 1680-7316 1680-7324 |