Evaluation of Asian Dust Absorption in Visible Band with Satellite Observation, Sky-radiometer Measurement, and Chemical Transport Model

Abstract

We assessed the spectral imaginary part of refractive index (n _i) of Asian dust aerosol in the visible wavelengths (0.412-0.865 µm) by comparing simulated and satellite-observed top of the atmosphere (TOA) reflectances. The approach employed in this study combines the results obtained from SeaWiFS ocean color sensor, the vertical profiles provided by CFORS mesoscale transport model, and the size distribution observed concurrently by Aerosol Robotic Network (AERONET) sites. Analyses for four dust instances over the Sea of Japan during 2001 and 2002 showed that the n _i values of Asian dust are significantly lower than previously published, as low as about 0.001 at 0.5 µm. Although the backward trajectories suggest that the four events have different sources, all events show very similar n _i values. The corresponding averaged coarse-mode dust single-scattering albedo (SSA) is found to be 0.98 ± 0.002 at 0.555 µm, which is consistent with the results of several contemporaneous observations conducted during Asian Aerosol Characterization Experiment (ACE-Asia). These results indicate that Asian dust particles itself may cool the climate system more strongly than is generally considered and a weakly absorbing model of Asian dust is more appropriate for use in climate modeling than the already used dust model.