 |
| Titel |
Investigating the scale-adaptivity of a shallow cumulus parameterization scheme with LES |
| VerfasserIn |
Maren Brast, Vera Schemann, Roel Neggers |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148059
|
| Publikation (Nr.) |
 EGU/EGU2017-12288.pdf |
|
|
|
|
|
| Zusammenfassung |
| In this study we investigate the scale-adaptivity of a new parameterization scheme for shallow
cumulus clouds in the gray zone. The Eddy-Diffusivity Multiple Mass-Flux (or ED(MF)n )
scheme is a bin-macrophysics scheme, in which subgrid transport is formulated in
terms of discretized size densities. While scale-adaptivity in the ED-component
is achieved using a pragmatic blending approach, the MF-component is filtered
such that only the transport by plumes smaller than the grid size is maintained. For
testing, ED(MF)n is implemented in a large-eddy simulation (LES) model, replacing
the original subgrid-scheme for turbulent transport. LES thus plays the role of a
non-hydrostatic testing ground, which can be run at different resolutions to study
the behavior of the parameterization scheme in the boundary-layer gray zone. In
this range convective cumulus clouds are partially resolved. We find that at high
resolutions the clouds and the turbulent transport are predominantly resolved by the
LES, and the transport represented by ED(MF)n is small. This partitioning changes
towards coarser resolutions, with the representation of shallow cumulus clouds
becoming exclusively carried by the ED(MF)n. The way the partitioning changes
with grid-spacing matches the results of previous LES studies, suggesting some
scale-adaptivity is captured. Sensitivity studies show that a scale-inadaptive ED component
stays too active at high resolutions, and that the results are fairly insensitive to the
number of transporting updrafts in the ED(MF)n scheme. Other assumptions in
the scheme, such as the distribution of updrafts across sizes and the value of the
area fraction covered by updrafts, are found to affect the location of the gray zone. |
|
|
|
|
|
|