A method to represent subgrid-scale updraft velocity in kilometer-scale models: Implication for aerosol activation

摘要: Updraft velocities strongly control the activation of aerosol particles or that component act as cloud condensation nuclei (CCN). For kilometer-scale models, vertical motions are partially resolved but subgrid-scale (SGS) contribution needs to be parametrized constrained properly represent CCNs. This study presents a method estimate missing SGS (or unresolved) velocity variability in models with horizontal grid sizes up ∼2 km. A framework based on Large Eddy Simulations (LES) and high-resolution aircraft observations stratocumulus shallow cumulus clouds has been developed applied output from United Kingdom Met Office Unified Model (UM) operating at resolutions numerical weather prediction configuration. deck simulation, we show UM 1 km model underestimates significantly updraft an averaged base standard deviation between 0.04 0.05 m s−1 compared LES estimates 0.38 0.54 s−1, respectively. Once is considered, corrected averages 0.34 0.44 s−1. Off-line calculations CCN-activated fraction using scheme have performed illustrate implication including velocity. It suggests increased 0.52 0.89 (respectively, 0.10 0.54) for clean polluted) environment simulations 1 km size. Our results highlight importance representing aerosol-cloud interactions.