Sensitivity studies using Regional Atmospheric Modeling System to analyze the impact of dust and aerosol on precipitation in the Colorado River Basin

Abstract:

A modeling study is performed in the Colorado River Basin by varying the ratio of dust and aerosol pollution. The Colorado State University Regional Atmospheric Modeling system (RAMS) version 6.0 is used for the analyses with the aerosol and dust pollution data being nudged from the GEOS-Chem. RAMS was modified to ingest GEOS-CHEM output data and periodically update aerosol fields. GEOS-CHEM is a chemical transport model which uses assimilated meteorological data from the NASA Goddard Earth Observation System (GEOS). The aerosol data comprise a sum of hydrophobic and hydrophilic black carbon and organic aerosol, hydrophilic SOAs, hydrocarbon oxidation and inorganic aerosols (nitrate, sulfate and ammonium). In addition, a RAMS-based dust source and transport model is used. The sensitivity studies are 5 different kinds. The base study has both the dust and aerosol pollution data ON. The Case 2 has dust OFF with only the aerosol sources ON. The Case 3 has the aerosol sources ON with dust multiplied by a factor of 3. Case 4 has the aerosol sources ON with dust multiplied by a factor of 10. Case 5 and Case 6 are the simulations where dust can act only as CCN and only as IN respectively. It was found that the precipitation increases when dust is increased 3 times. However, the response is non-monotonic when dust is increased 10 times and the response depends on the environmental conditions. Dust acting as CCN acts in opposition to dust acting as IN. In general, dust acting as IN tends to enhance precipitation in wintertime orographic clouds.