This talk presents three-dimensional numerical simulations of oceanic trade cumulus clouds underlying stratocumulus clouds. It is based on a Global Energy and Water Experiment (GEWEX) Cloud System Study (GCSS) model intercomparison that is loosely based on observed conditions during the Atlantic Trade Cumulus Experiment (ATEX). It is motivated by the importance of this cloud type to global cloud radiative forcing, and its role as a feeder system for deep convection in the tropics. This study focuses on the sensitivity of the modeled cloud field to the domain size and the grid spacing by studying two sequences of simulations with different domain widths of 6.4 and 20.2 kilometers. Each sequence contains simulations where the horizontal mesh spacing ranged from 10 to 80 meters and the vertical from 5 to 40 m. The combination of large domain size and small grid resolution (up to 2.5 billion grid-cells) provides an unprecedented perspective on this type of convection. This is in contrast to Prior LES simulations which have often used domains a few kilometers wide. The larger domain size considered here is comparable to the grid resolution of a typical current mesoscale model (a similar resolution will soon be achieved in some global weather forecast models), and can better represent the potential horizontal variability achievable within a mesoscale grid cell.
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