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Impact of 3D Clouds on Aerosol Retrievals

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. Physical Mechanism. r 1D. D r. additional diffuse radiation source scattered by clouds.

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Impact of 3D Clouds on Aerosol Retrievals

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  1. Impact of 3D Clouds on Aerosol Retrievals Guoyong Wen1,2 Alexander Marshak1 Robert F. Cahalan1 Lorraine Remer1 Richard Kleidman1,3 1NASA/Goddard Space Flight Center 2GEST/UMBC, 3SSAI

  2. Physical Mechanism r1D Dr additional diffuse radiation source scattered by clouds 3D impact Dr= r3D - r1D

  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 10mm • Log-normal distribution of aerosols with re=0.13mm, and s=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. Monte Carlo Simulation of 3D Cloud Effects Simulated 3D cloud effects defined as Dr = r3D-r1D at 1km resolution AOT = 0.1

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

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

  12. Some Details

  13. More Details with ASTER

  14. 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 0.47mm (AOT=0.4) 0.67mm (AOT = 0.2) Dr ~ 0.015 or Dt ~ 0.15 Dr ~ 0.02 or Dt ~ 0.2 Assume Dt is a linear function of t, i.e., Dt = a t, we estimate AOT=0.27 andAOT ~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 0.67mm and 0.47mm respectively rather than 0.2 and 0.4 in an open area of Cu.

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