 |
| Titel |
Towards a Lagrangian mixing scheme at the stratocumulus cloud top |
| VerfasserIn |
Lukas Müßle, Alberto de Lozar, Juan-Pedro Mellado |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096911
|
| Publikation (Nr.) |
 EGU/EGU2014-12443.pdf |
|
|
|
|
|
| Zusammenfassung |
| Mixing processes at the top of stratocumulus clouds are still not well understood. This causes
uncertainty in weather and climate predictions of the subtropics and polar regions, where
stratocumuli play an important role. Parameterizations of mixing are usually based on high
resolution models, but these might be hampered by a lack of understanding of the interaction
of the droplet dynamics with small scale turbulence. For example, most models assume
thermodynamic equilibrium for the droplets but in reality it takes a finite time to reach
this thermodynamic equilibrium. Moreover it is assumed that cloud droplets are
equally distributed over the cloud domain, but the droplets have a tendency to prefer
regions with lower vorticity. Both factors could be an important factor for the cloud
mixing.
To investigate the microphysical droplet dynamics in a cloud, both Eulerian and Lagrangian
schemes can be used. In a traditional Eulerian approach all droplets are treated as a
continuum field. This approach is computationally much cheaper than the Lagrangian one,
but it is known to introduce extra diffusion and to smooth out fluctuations of the droplet
dynamics. In order to resolve the mixing dynamics more accurately, a Lagrange approach can
be used. Here the equations of motion are solved individually for each droplet, and the
droplet dynamics are coupled to the flow equations. This approach needs much more
computational resources than the Eulerian approach. Therefore, simulations using a
Lagrangian description are limited to small domains. Despite the more extensive numerical
effort and costs, the application of this method in some idealized configurations could
reduce uncertainties regarding the role of microphysical dynamics in the mixing
process.
Our goal is to develop a Lagrangian scheme to work in high resolution simulations of the
stratocumulus cloud top. We use Direct Numerical Simulations for the flow, which is then
coupled to the Lagrangian scheme. We want to compare our Lagrangian results to fully
Eulerian simulations, in order to determine the major differences of both schemes. We are
particularly interested in quantifying the deviations in the mixing introduced by the
Eulerian scheme. Furthermore, we want also to explore the effect of mixing on the
droplet radius spectrum and to asses which model of the mixing (homogeneous
or inhomogeneous) fits better for the mixing at the top of stratocumulus clouds. |
|
|
|
|
|
|