1. Impact of 3D Clouds on Aerosol Retrievals Guoyong Wen 1,2 Alexander Marshak 1 Robert F. Cahalan 1 Lorraine Remer 1 Richard Kleidman 1,3 1 NASA/Goddard Space Flight Center 2 GEST/UMBC, 3 SSAI

2. Physical Mechanism r 1D additional diffuse radiation source scattered by clouds rr 3D impact  r= r 3D - r 1D

3. Monte-Carlo Simulation of Radiation Fields of a sub-image of a MODIS image about the size of ASTER image (60 km x 60 km) at 53 degrees west on the equator, acquired on Jan 25, 2003. 60km

4. Monte Carlo Simulation of Radiation Field Inputs: MODIS cloud OPD Cloud top height derived from the Tb at 11 microns Cloud bottom at 1 km Effective radius of 10  m Log-normal distribution of aerosols with r e =0.13  m, and  =0.7. Surface albedo of 0.023 SZA of 32 degrees SAM of 129 degrees Simulate 3D radiaiton field in 90m resolution using ASTER Exam: 3D cloud impacts Analyze MODIS aerosol retrievals Detailed analysis

5. MODIS Cloud Optical Depth And Brightness Temperature

6. Simulated 3D cloud effects defined as  r = r 3D -r 1D at 1km resolution AOT = 0.1 Monte Carlo Simulation of 3D Cloud Effects

7. The distribution shows the shadowing reduction and diffuse enhancement.  r~0.004 or  ~0.04 for  =0.1 Statistics of 3D Cloud Effects

8. MODIS Selected Pixels for Aerosol Retrievals And Retrieved Aerosol Optical Thickness

9. It appears more open the smaller reflectance the closer the pixels to bright clouds, the larger reflectance occurs the selected clear pixels are quite homogeneous. the reflectance of those pixels show slightly dependence on clear-cloud distance

10. Intercomparison of Observed and MC Simulated Selected Clear Pixel Reflectance

11. Observed Reflectance is linear correlated with Modeled reflectance with correlation coefficient of 0.75. Intercomparison of Observed and MC Simulated Reflectance for Selected Clear Pixels

12. Some Details

13. More Details with ASTER

15. 3D Cloud Effects from ASTER

16. Derived Cloud Optical Depth Field and Cloud Top Height at 90 m Resolution

17. MC Simulated 3D Cloud Effects

18. 3D Cloud Enhancement and Distribution As A Function of Nearest Cloud Distance  r ~ 0.02 or  ~ 0.2 0.47  m (AOT=0.4)0.67  m (AOT = 0.2)  r ~ 0.015 or  ~ 0.15 Assume  is a linear function of  i.e.,  we estimate AOT=0.27 and AOT ~0.11

19. Summary MODIS aerosol retrieval algorithm does a good job to select homogeneous targets. 3D clouds strongly enhance clear sky reflectance nearby. This effect can be seen from ASTER images. Estimated error in 1D AOT is large. Aerosol optical thickness is about 0.11 and 0.27 at 0.67  m and 0.47  m respectively rather than 0.2 and 0.4 in an open area of Cu.