Similarities and differences between Asian and Saharan dust from models, satellite- and ground-based data

A three-dimensional coupled climate-aerosol microphysical sectional model based on the University of Colorado/NASA Community Aerosol and Radiation Model for Atmospheres (CARMA2.3) and the NCAR Community Atmosphere Model (CAM3) is used along with data to understand the similarities and differences between dust from Asia and dust from the Sahara. The simulated dust vertical distributions of Saharan and Asian dust are constrained by CALIPSO (lidar) measurements in 2006 and 2007. The size distributions and single scatter albedo of Saharan and Asian dust are validated by AERONET data in May and July 2007. Saharan deserts are largely south of 30N, while Asian ones are primarily north of 30N, hence they experience different meteorological regimes. Saharan dust lifting occurs all year long, primarily due to subtropical weather systems. However, Asian dust is lifted mostly in spring when mid-latitude frontal systems lead to high winds. Rainfall is more abundant over Asia during the dust lifting events, leading to greater local dust removal than over the Sahara. Asia also has more vegetation and snow cover, which suppresses dust lifting. As a result of these factors the yearly horizontal dust flux just downwind of the African dust source is about 1550 Tg (10S-40N, 10E) and from the Asian dust source it is about 420 Tg (25N-55N, 105E) in 2007. Despite the different meteorological regimes, the same dust lifting schemes work in models for Asian and the Saharan dust. Once lifted, the Saharan dust layers generally move toward the west and descend in altitude from about 7km to the surface over several days in the cases studied. Asian dust often has multiple layers (two layers in the cases studied) during transport. One layer stays well above boundary layer during transport and shows little descent, while the other, lower layer descends with time. This observation contrasts with studies suggesting the descent of Saharan dust is due to sedimentation of the particles, and suggests instead it is dominated by meteorology. While we find the size distributions of Asian and African dust are similar for similar distances from the source, the imaginary parts of the refractive indexes are different. This study is a step towards a global understanding of dust and its properties.