Observations and Modeling of Shallow Convective Clouds: Implications for the Indirect Aerosol Effects
| Sylwester Arabas | Institute of Geophysics, University of Warsaw |
| Joanna Slawinska | Institute of Geophysics, University of Warsaw |
| Wojciech Grabowski | National Center for Atmospheric Research |
| Hugh Morrison | National Center for Atmospheric Research |
| Hanna Pawlowska | Institute of Geophysics, University of Warsaw, Poland |
Category: Cloud Properties
Chosson et al. (2007), Grabowski (2006), and Slawinska et al. (2008) showed that assumptions about microphysical transformations during entrainment and mixing (i.e., the homogeneous versus inhomogeneous mixing) have a significant impact on the albedo of a field of shallow convective clouds. This is because of a significant dilution of these clouds due to entrainment of dry environmental air and the complexity of the small-scale mixing and homogenization. This aspect is especially relevant for the estimate of the indirect aerosol effects, that is, the change of the mean albedo (either through the changes of cloud properties or changes of the cloud fraction) as a result of a change of cloud condensation nuclei. To simulate the indirect effects on shallow warm (ice-free) clouds, a double-moment bulk warm-rain microphysics scheme has been developed recently and validated by Morrison and Grabowski (2007). The scheme predicts number concentrations and mixing ratios for cloud droplets and for drizzle/rain drops, and the evolution of the supersaturation field. A novel feature of the scheme is that it allows prescribing the homogeneity of the mixing, from the homogeneous to extremely inhomogeneous. This paper will present results of the application of the scheme to simulations of shallow convection observed during the Rain in Cumulus over Ocean (RICO) field project. Statistical properties of model-simulated clouds will be compared with the statistics gathered in situ by the instrumented aircraft. Chosson, F, J-L Brenguier, and L Schuller. 2007. "Entrainment-mixing and radiative transfer simulation in boundar layer clouds." Journal of Atmospheric Sciences 64, 7, 2670-2682. Grabowski, WW. 2006. "Indirect impact of atmospheric aerosols in idealized simulations of convective-radiative quasi equilibrium." Journal of Climate 19, 18, 4664-4682. Morrison, H, and WW Grabowski. 2007. "Comparison of bulk and bin warm-rain microphysics models using a kinematic framework." Journal of Atmospheric Sciences 64, 8, 2839-2861. Morrison, H, and WW Grabowski. 2008. "Modeling supersaturation and subgrid-scale mixing with two-moment bulk warm microphysics." Journal of Atmospheric Sciences 65, 3, 792-812. Slawinska, J, WW Grabowski, H Pawlowska, and AA Wyszogrodzki. 2008. "Optical properties of shallow convective clouds diagnosed from a bulk-microphysics large-eddy simulation." Journal of Climate 21, 7, 1639-1647.
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