Atmos. Chem. Phys. Discuss., 8, 15291-15341, 2008
www.atmos-chem-phys-discuss.net/8/15291/2008/
doi:10.5194/acpd-8-15291-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Cloud and aerosol effects on radiation in deep convective clouds: comparison with warm stratiform clouds
S. S. Lee1,*, L. J. Donner1, and V. T. J. Phillips1,**
1Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, NJ, USA
*now at: Department of Atmospheric, Oceanic, and Space Science, University of Michigan, Ann Arbor, MI, USA
**now at: Department of Meteorology, University of Hawaii, Manoa, HI, USA

Abstract. Cloud and aerosol effects on radiation in two contrasting cloud types, a deep convective mesoscale cloud ensemble (MCE) and warm stratocumulus clouds, are simulated and compared. At the top of the atmosphere, 45–81% of shortwave cloud forcing (SCF) is offset by longwave cloud forcing (LCF) in the MCE, whereas warm stratiform clouds show the offset of less than ~20%. 28% of increased negative SCF is offset by increased LCF with increasing aerosols in the MCE at the top of the atmosphere. However, the stratiform clouds show the offset of just around 2–5%. Ice clouds as well as liquid clouds play an important role in the larger offset in the MCE. Hence, this study indicates effects of deep convective clouds on radiation and responses of deep convective clouds to aerosols are quite different from those of shallow clouds through the different modulation of longwave radiation; the presence of ice clouds in deep convective clouds contributes to the different modulation of longwave radiation significantly. Different cloud types, characterized by cloud depth and cloud-top height, play critical roles in those different modulations of LCF between the MCE and stratocumulus clouds. Lower cloud-top height and cloud depth lead to smaller offset of SCF by LCF and offset of increased negative SCF by increased LCF at high aerosol in stratocumulus clouds than in the MCE. Supplementary simulations show this dependence of modulation of LCF on cloud depth and cloud-top height is not limited to those two contrasting cloud types. The dependence is also simulated among different types of convective clouds, indicating the assessment of effects of varying cloud types on radiation due to climate changes can be critical to better prediction of climate.

Citation: Lee, S. S., Donner, L. J., and Phillips, V. T. J.: Cloud and aerosol effects on radiation in deep convective clouds: comparison with warm stratiform clouds, Atmos. Chem. Phys. Discuss., 8, 15291-15341, doi:10.5194/acpd-8-15291-2008, 2008.
 
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