P21     Mass-flux parameterization of turbulent downdrafts in marine stratocumulus clouds.

Wu, Elynn, Handa Yang, Jan Kleissl, Center for Renewable Resource and Integration, Department of Mechanical and Aerospace Engineering, University of California, Kay Suselj, Marcin J. Kurowski, and Joao Teixeira, Jet Propulsion Laboratory, California Institute of Technology

To better estimate vertical mixing in Weather Research and Forecasting (WRF) in simulations of stratocumulus-topped boundary layers (STBL), we employ the eddy-diffusivity/mass-flux (EDMF) framework which decomposes the subgrid vertical mixing into local mixing through ED and non-local transport through convective plumes. As part of the non-local mass-flux transport, we propose a scheme for radiatively-cooled downdrafts that enhances the existing surface-driven updraft scheme implemented as an add-on option within Mellor-Yamada-Nakanishi-Niino (MYNN) planetary boundary layer (PBL) scheme. We modified the existing updraft scheme to account for the strong inversion in STBL, limiting the updraft penetration in regions where strong stability is present. Downdraft properties for the WRF parameterization are derived from two typical STBL large eddy simulation (LES) runs. In the LES, the downdraft and updraft contributions to the total heat and moisture transport in the PBL are comparable. The downdraft parameterization is implemented in MYNN and tested in the WRF single column model. The results show good agreement between parameterized downdraft turbulent transport and LES, while contribution from ED changes in the absence of updrafts and downdrafts. We investigate the roles of ED, updrafts, and downdrafts to the total turbulent heat and moisture transport in WRF.