Atmos. Chem. Phys. Discuss., 12, 29099-29127, 2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
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-resolving modeling of aerosol indirect effects in idealized radiative-convective equilibrium with interactive and fixed sea surface temperature
M. F. Khairoutdinov1 and C.-E. Yang1,*
1School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, USA
*now at: Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN, USA

Abstract. The study attempts to evaluate the aerosol indirect effects over tropical oceans in regions of deep convection applying a three-dimensional cloud-resolving model run over a doubly-periodic domain. The Tropics are modeled using a radiative-convective equilibrium idealization when the radiation, turbulence, cloud microphysics, and surface fluxes are explicitly represented while the effects of large-scale circulation are ignored. The aerosol effects are modeled by varying the number concentration of cloud condensation nuclei (CCN) at 1% supersaturation, which serves as a proxy for the aerosol amount in the environment, over a wide range, starting from pristine maritime (50 cm−3) to polluted (1000 cm−3) conditions. No direct effects of aerosol on radiation are included. Two sets of simulations have been run to equilibrium: fixed (non-interactive) sea surface temperature (SST) and interactive SST as predicted by a simple slab-ocean model responding to the surface radiative fluxes and surface enthalpy flux. Both sets of experiments agree on the tendency to make the shortwave cloud forcing more negative and reduce the longwave cloud forcing in response to increasing CCN concentration. These, in turn, tend to cool the SST in interactive-SST case. It is interesting that the absolute change of the SST and most other bulk quantities depends only on relative change of CCN concentration; that is, same SST change can be the result of doubling CCN concentration regardless of clean or polluted conditions. It is found that the 10-fold increase of CCN concentration can cool the SST by as much as 1.5 K. This is quite comparable to 2 K warming obtained in a simulation for clean maritime conditions, but doubled CO2 concentration. Qualitative differences between the interactive and fixed SST cases have been found in sensitivity of the hydrological cycle to the increase in CCN concentration; namely, the precipitation rate shows some tendency to increase in fixed SST case, but robust tendency to decrease in interactive SST case.

Citation: Khairoutdinov, M. F. and Yang, C.-E.: Cloud-resolving modeling of aerosol indirect effects in idealized radiative-convective equilibrium with interactive and fixed sea surface temperature, Atmos. Chem. Phys. Discuss., 12, 29099-29127, doi:10.5194/acpd-12-29099-2012, 2012.
Search ACPD
Discussion Paper
    Final Revised Paper