Aerosol radiative characteristics at Gosan, Korea, during the Atmospheric Brown Cloud East Asian Regional Experiment 2005

The ABC (Atmospheric Brown Cloud project) Gosan campaign 2005 (EAREX2005) was carried out at Gosan on Cheju Island, Korea, in March 2005. The objective of the campaign was to clarify aerosol characteristics as well as to compare each instrument for radiation and chemical observation. From these observations, eleven clear sky cases were selected and analyzed to estimate the aerosol radiative effect (ARE). As a result, the mean ARE during the campaign was -20.8 ± 9.0 W/m² at the surface, -8.3 ± 5.3 W/m² at the top of the atmosphere and 12.6 ± 6.8 W/m² in the atmosphere. The ARE efficiency was -81.6 W/m², -32.5 W/m² and 49.4 W/m², respectively. These results suggest that the aerosols during the campaign might consist of more or less yellow sand in comparison with the results simulated using typical aerosol models. On the basis of simultaneous observation of the depolarization ratio by lidar, a common feature of yellow sand is also found in a daily trend of aerosols through the period. A yellow sand index (YSI) is introduced using a column integration of extinction coefficients for spherical and nonspherical particles, separated empirically by the depolarization ratio. This index is equivalent to the fraction of yellow sand (nonspherical) aerosol in the observed aerosol optical thickness. The YSI has a good correlation with the Angstrom index (α) obtained by sky radiometer observations and shows that the increase in YSI corresponds to the decrease in α and the increase in single scattering albedo of aerosol. However, the YSI is poorly correlated with the ARE efficiency.