2014 Volume 92A Pages 33-56
The Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) project initiated an intensive field experiment on dust aerosols in Dunhuang from April 1 to June 12, 2012. Using sky radiometer measurements and conducting model simulations, we investigated the dust aerosol characteristics and its shortwave radiative impact on the regional climate. The daily averaged optical features of the aerosols markedly varied throughout the study period. High aerosol loading and predominantly coarse particulates were observed in the spring of 2012 ascribed to the influence of prevalent dust storm. The single scattering albedo at 500 nm (SSA500) varied from 0.91 to 0.97 on dusty days and from 0.86 to 0.91 on dust-free days, indicating that the dust aerosols sourced from northwest China were not strongly absorbing. Surface radiation quantities estimated by the radiative transfer model excellently agreed with ground-based and satellite observations, with correlation coefficients exceeding 0.990 and mean differences ranging from -3.9 to 17.0 W m-2. The daily mean aerosol shortwave direct radiative forcing (ARF) values were largely negative at the surface (-79.4 to -3.2 W m-2) and moderately positive in the atmosphere (2.2-25.1 W m-2), indicating strong cooling at the surface and moderate atmospheric warming. The monthly averaged ARFEs (ARFs per unit aerosol optical depth at 500 nm (AOD500)) at the surface were (-73.9 ± 11.6) W m-2, (-67.4 ± 8.3) W m-2, and (-74.4 ± 5.4) W m-2 in April, May, and June, respectively (overall average of (-70.8 ± 7.9) W m-2), comparable to previously obtained values in East Asia and India domains. The relations between the diurnal ARFs at the surface and top of the atmosphere (TOA) and the AOD500 indicate that aerosol composition remained relatively stable at Dunhuang during the spring of 2012. The ARF at the TOA was positive for SSA500 less than 0.85 or when the imaginary part at 500 nm exceeded 0.015.