On the parameterization of convective downdrafts to represent marine stratocumulus clouds
Abstract
The role of non-local transport on the development and maintenance of marine stratocumulus in coarse resolution models is investigated, with a special emphasis on the downdraft contribution. A new parameterization of cloud-top triggered downdrafts is proposed and validated against large-eddy simulation (LES). The applied non-local mass-flux scheme is part of the stochastic multi-plume eddy-diffusivity/mass-flux (EDMF) framework decomposing the turbulence into local and non-local contributions. The eddy-diffusivity (ED) transport is represented with the Mellor-Yamada-Nakanishi-Niino (MYNN) scheme. This EDMF scheme has been implemented in the WRF single-column model (SCM) and tested for three simulations: without mass flux, with updrafts only, and with both updrafts and downdrafts. In the LES, the downdraft and updraft contributions to the total heat and moisture transport are comparable and significant. Two idealized cases are simulated in both LES and WRF. The WRF SCM results show a good agreement between the parameterized downdraft turbulent transport and LES, while the ED parameterization adjusts dynamically to the amount of non-local MF present. From the two idealized cases, results suggest that while it is more important to include updrafts, the inclusion of downdrafts leads to some improvement on the modeling of Sc clouds. To test how MF parameterization responds to changes in physical parameters that control marine stratocumulus, additional sensitivity tests are performed by switching off radiation and setting surface fluxes to zero. We hypothesis that contribution to turbulent transport from downdrafts decreases without radiation and increases without surface fluxes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A41L2737W
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3379 Turbulence;
- ATMOSPHERIC PROCESSES