Modeling the emission, transport, and optical properties of Asian dust storms using coupled CAM/CARMA model Lin Su and Owen B. Toon Laboratory for Atmospheric and Space Physics Department of Atmospheric and Oceanic Sciences University of Colorado at Boulder AMWG/NCAR Feb. 13, km

Outline 1.Model configuration 2.Modified dust source function 3.Sub-grid scale velocity distribution 4.Effective dry deposition velocity 5.Transport and optical properties 6.Summary 7.Future work

Model descriptions CAM3 (NCAR Community Atmosphere Model) CARMA2.3(the University of Colorado/NASA Community Aerosol and Radiation Model for Atmospheres) Finite Volume dynamical core Horizontal resolution: 2 x 2.5 degrees 28 vertical model layers Ginoux et al. [2001] dust lifting scheme 8 dust size bins (ranging from um radius)

NCEP Reanalysis Initialization Meteorology fields CAM3 CARMA2.3 state tendencies Emission Sedimentation Advection Convection Boundary layer mixing Wet deposition Dry deposition Model output Dust MMR Dust concentration AOD SSA Extinction, etc.

JAPAN CHINA Taklimakan Gobi RUSSIA Beijing 10/27/2001

Wind Field Friction Velocity Under unstable, neutral and stable conditions Replace u10

Sub-grid scale velocity distribution The Ginoux et al. [2001] dust source functions has the form : Where is the incomplete gamma function given by (1) Following Gillette and Passi [1988], after integrated formula (1) from the threshold wind velocity to infinity, we got the Weibull distribution of the dust lifting schemes as follows: The shape factor and scale factor following Grini and Zender [2004]

The ratio of dust emission w/ weibull wind distribution and w/o weibull wind distribution (April 7, 2001)

Dust Dry Deposition Process The dry deposition velocities - following Seinfeld & Pandis [1998]: Account for soil moisture: the effective dry deposition velocity - Ginoux et al. [2001]: The eqn. in Seinfeld and Pandis don't produce the correct gradients when the fall velocity is large. They are derived incorrectly when falling is occurring.

Beijing Surface Dust Optical Depth on April 10, 2001

Observation and model simulation is 0.947and at 550nm South Asia: 0.90 at 532nm [Muller et al., 2003] Sahara Desert: < 0.90 at 550nm [Takemura et al., 2002; Sokolik and Toon, 1999] Single Scattering Albedo for Dunhuang, China on April 07, 2001

Modeled dust mass density for Beijing (g/cm3)

Summary 1.I modified Ginoux et al. [2001] dust source function by using the friction velocity instead of the 10-meter wind based on the wind erosion theory and saltation physical process. 2.I introduced the Weibull wind distribution to use sub-grid scale velocity distribution, and results in up to 1.25 times of dust lifting. 3.The aerosol optical depths and single scattering albedo agree with the ground-based AERONET retrievals. However, I haven’t included air pollutants from China. 4. The vertical profiles of dust are comparable to the ACE- Asia 2001 NIES-lidar observations in Beijing.

Future Work 1.Compare the results with new satellite retrievals (MODIS Deep-Blue) and for other time periods (PACDEX). Constrain dust height by MISR stereo plume product and CALIPSO lidar data. 2.Run the model in an offline mode at higher resolution using the GEOS-5 DAS at 0.5x0.666 degrees. 3. Study the relationship between drought cycles and dust storms in Asia area