Potential impacts of dust on precipitation in the Colorado River Basin

The SW United States has huge demands on water resources. Colorado River Basin (CRB) is potentially affected by aerosol pollution and dust acting as cloud-nucleating aerosol as well as impacting snowpack albedo. Dust can affect precipitation processes. Considering that the basis behind cloud seeding is to enhance precipitation by enhancing IN concentrations we anticipate that dust serving as IN will enhance precipitation in wintertime orographic clouds. Dust serving as GCCN should enhance precipitation, thus support the activity of IN. Dust functioning as CCN will work in opposition to its activity as GCCN and IN and suppress precipitation. We anticipate that this would be the case for wintertime orographic clouds as well. We intend to examine the combined effects of dust serving as IN, GCCN, and CCN on precipitation and on water resources in the CRB for the period of Oct to Apr from 2005-2008. Dust will be initialized from the GEOS-chem model for the shorter runs. For the entire seasonal runs for the four years the GEOS-chem would be nudged to obtain the dust fields. The Colorado State University Regional Atmospheric Modeling System version 6.0 is used for the simulation. The 32km North American Regional Reanalysis is used for model initialization. RAMS spec: (Grid1=36 km, 85×75 points, Grid 3=3 km; 146×150 points, 45 stretch levels, 75 m at surface to 800 m aloft, Two-moment bin-emulating microphysics, DeMott et al., 2010, heterogeneous ice nucleation). Preliminary results correspond to two 48-hour periods, (Apr 12 and Apr 29 2005) in the San Juan region in the Rocky Mountains. Dust serving as CCN acts to enhance ice particle riming along with dust acting as GCCN, and since dust enhances IN, total precipitation is enhanced in a dustier atmosphere.