Controlling factors of continental shallow cumulus clouds – sensitivity tests of LES and ACME single-column model on a new composite SGP case
Poster PDF
Authors
Yunyan Zhang — Lawrence Livermore National Laboratory
Stephen Klein — Lawrence Livermore National Laboratory
Wuyin Lin — Brookhaven National Laboratory
Shaocheng Xie — Lawrence Livermore National Laboratory
Category
Warm low clouds, including aerosol interactions
Description
Based on long-term, diurnal-cycle observations at the ARM SGP site, a new composite case of continental active shallow cumulus (ShCu) convection is built for large-eddy simulations (LES) and single-column models (SCM). This case represents a typical daytime, non-precipitating, fair-weather ShCu, the formation and dissipation of which are driven by the local atmospheric conditions and land-surface forcing, and are not influenced by synoptic weather events. The case includes: early morning initial profiles of temperature and moisture with a residual layer; diurnally varying sensible and latent heat fluxes that represent a domain average over different land-surface types; simplified large-scale horizontal advective tendencies and subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation (Zhang et al., 2016).
In this study, based on this new active ShCu composite case, a series of sensitivity simulations are done for LES and SCM with the exact same sets of initial and boundary conditions and large-scale forcings. Sensitivity tests are designed to reflect the variability in environmental factors among the ShCu days that are included in this active ShCu composite and the difference in the environmental factors among the composites of different convective regimes such as forced and active ShCu and the ShCu that transits to late-afternoon deep convections. On one hand, the LES sensitivity runs are used to validate the mechanisms controlling the variability of ShCu and the transitions between convection regimes in our observational findings (Zhang and Klein, 2010, 2013). On the other hand, the LES runs are used to evaluate the performance of the newly developed single-column version of the DOE ACME atmospheric model component on simulating continental ShCu.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
LLNL-ABS-716536
