Theoretical analysis of mixing in liquid clouds – Part 3: Inhomogeneous mixing
An idealized diffusion–evaporation model of time-dependent mixing between a cloud volume and a droplet-free volume is analyzed. The initial droplet size distribution (DSD) in the cloud volume is assumed to be monodisperse. It is shown that evolution of the microphysical variables and the final eq...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/9273/2016/acp-16-9273-2016.pdf |
| Summary: | An idealized diffusion–evaporation model of time-dependent mixing between a
cloud volume and a droplet-free volume is analyzed. The initial droplet size
distribution (DSD) in the cloud volume is assumed to be monodisperse. It is
shown that evolution of the microphysical variables and the final equilibrium
state are unambiguously determined by two non-dimensional parameters. The
first one is the potential evaporation parameter <i>R</i>, proportional to the
ratio of the saturation deficit to the liquid water content in the cloud
volume, that determines whether the equilibrium state is reached at 100 %
relative humidity, or is characterized by a complete evaporation of cloud
droplets. The second parameter <i>Da</i> is the Damkölher
number equal to the ratio of the characteristic mixing time to the phase
relaxation time. Parameters <i>R</i> and <i>Da</i> determine the type of mixing.<br><br>The results are analyzed within a wide range of values of <i>R</i> and
<i>Da</i>. It is shown that there is no pure homogeneous mixing, since the
first mixing stage is always inhomogeneous. The mixing type can change during
the mixing process. Any mixing type leads to formation of a tail of small
droplets in DSD and, therefore, to DSD broadening that depends on
<i>Da</i>. At large <i>Da</i>, the final DSD dispersion can be as large
as 0.2. The total duration of mixing varies from several to 100 phase
relaxation time periods, depending on <i>R</i> and <i>Da</i>.<br><br>The definitions of homogeneous and inhomogeneous types of mixing are
reconsidered and clarified, enabling a more precise delimitation between
them. The paper also compares the results obtained with those based on the
classic mixing concepts. > |
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| ISSN: | 1680-7316 1680-7324 |