Illustration of microphysical processes in Amazonian deep convective clouds in the gamma phase space: introduction and potential applications
The behavior of tropical clouds remains a major open scientific question, resulting in poor representation by models. One challenge is to realistically reproduce cloud droplet size distributions (DSDs) and their evolution over time and space. Many applications, not limited to models, use the gamm...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/14727/2017/acp-17-14727-2017.pdf |
| Summary: | The behavior of tropical clouds remains a major open scientific question,
resulting in poor representation by models. One challenge is to realistically
reproduce cloud droplet size distributions (DSDs) and their evolution over
time and space. Many applications, not limited to models, use the gamma
function to represent DSDs. However, even though the statistical
characteristics of the gamma parameters have been widely studied, there is
almost no study dedicated to understanding the phase space of this function
and the associated physics. This phase space can be defined by the three
parameters that define the DSD intercept, shape, and curvature. Gamma phase
space may provide a common framework for parameterizations and
intercomparisons. Here, we introduce the phase space approach and its
characteristics, focusing on warm-phase microphysical cloud properties and
the transition to the mixed-phase layer. We show that trajectories in this
phase space can represent DSD evolution and can be related to growth
processes. Condensational and collisional growth may be interpreted as
pseudo-forces that induce displacements in opposite directions within the
phase space. The actually observed movements in the phase space are a result
of the combination of such pseudo-forces. Additionally, aerosol effects can
be evaluated given their significant impact on DSDs. The DSDs associated with
liquid droplets that favor cloud glaciation can be delimited in the phase
space, which can help models to adequately predict the transition to the
mixed phase. We also consider possible ways to constrain the DSD in
two-moment bulk microphysics schemes, in which the relative dispersion parameter
of the DSD can play a significant role. Overall, the gamma phase space
approach can be an invaluable tool for studying cloud microphysical evolution
and can be readily applied in many scenarios that rely on gamma DSDs. |
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| ISSN: | 1680-7316 1680-7324 |