# Presentation: 003378

## Aerosol-Cloud Interactions and Radiative Forcing: Modeling and Observations 

**Aerosol-Cloud Interactions and Radiative Forcing: Modeling and Observations**

- Graham Feingold1, K. S. Schmidt2, H. Jiang3, P. Zuidema4, H. Xue5, P. Pilewskie2, A. Hill1, H. Wang1

- 1NOAA Earth Systems Research Laboratory (ESRL), Boulder, CO; 2Univ. Of Colorado, Boulder, CO; 3CIRA/NOAA/ESRL, Boulder, CO; 4University of Miami, Miami, FL, 5Beijing University, China

**Acknowledgements: **
- _Funding:_ DOE/ARM (DE-AI02-06ER64215), NOAA’s Climate Goal

**References**
- Hill, A., G. Feingold, H. Jiang: The influence of mixing on the climate forcing of non-precipitating marine stratocumulus, 2008: J. Atmos. Sci., submitted.
- Jiang, H., G. Feingold, et al., 2008:** **Comparison of statistical properties of simulated and observed cumulus clouds in the vicinity of Houston
- 	during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS). J. Geophys. Res., in press.
- Schmidt, K. S., P. Pilewskie, G. Feingold, and H. Jiang, 2008: Irradiance from fields of shallow cumulus clouds: Measurements vs. radiative transfer modeling based 	on clouds generated by a large eddy simulation. In preparation.
- Wang, S., Q. Wang, and G. Feingold, 2003: Turbulence, condensation and liquid water transport in numerically simulated nonprecipitating stratocumulus clouds. J. 	Atmos. Sci., 60, 262-278.
- Xue, H., G. Feingold, and B. Stevens, 2008: Aerosol effects on clouds, precipitation, and the organization of shallow cumulus convection. J. Atmos. Sci., 65, 392-406.
- Zuidema, P., H. Xue, and G. Feingold, 2008: Shortwave radiative impacts from aerosol effects on marine shallow cumuli. J. Atmos. Sci., in press.

**Introduction**

*The effect of aerosol on cloud microphysics** **≠ **aerosol indirect effect !!*
- The indirect effect involves radiative forcing and depends on
-  cloud microphysical response,
-  macroscale properties (cloud fraction, cloud depth, distances between clouds)
-  aerosol between clouds
- We demonstrate this via:
- 	1. comparisons between measured irradiance fields for a field of cumulus 	      		      clouds, and irradiance fields calculated based on large eddy simulations of 	      these clouds;
- 	2. calculations of the relative contributions of the microphysical and  	  	     		     macrophysical responses to an aerosol perturbation for modeled cloud 	  	     fields;
- 	3. demonstrations of how sensitive the representation of aerosol-cloud 	  	     interactions is to the representation of entrainment-mixing, and;
- 	4. simulations of the transition from closed cell convection to pockets of open 	     cells provide an example of how aerosol, through its effect on 	   	    	     precipitation, can very effectively change radiative forcing;

- 1.

- Grey lines: inhomogeneous mixing
- Black lines: Homogeneous mixing

- polluted (dashed)

- clean

- z = 20m

- z = 5 m

- 4. Sensitivity of Aerosol-Cloud interactions to Entrainment-Mixing: LWP

- 3.

- 2.

**Conclusions**
*Statistical sampling of shallow cumulus allowed comparison with LES*
*	**output. Good comparison for LWP, drop concentration, updraft*
*	**Irradiance field below cloud compares well *_*provided aerosol between *_
*	*_*clouds is accounted for.*_
*In small cumulus, microphysical responses to aerosol perturbations may*
*	**counteract morphological responses (cloud fraction, LWP). This reduces*
*	**indirect effect response and albedo susceptibility may be *_*non-monotonic*_*.*
*Drizzle in stratocumulus is shown using LES to result in the formation of *
*	**open cellular structure.  **	*
*LWP is shown to *_*decrease*_* with increasing aerosol in non-precipitating *
*stratocumulus as a result of an evaporation-entrainment feedback*

*Non-monotonic response of cloud fraction to increases in aerosol*

*Drizzle transforms closed cellular convection to open cellular convection*

- See also Wang et al., 2003

*Aerosol perturbations result in a decrease in LWP in non-precipitating warm clouds*
*Entrainment-mixing affects the magnitude of the response*