摘要：Aerosols impact clear-sky surface irradiance ( ) through the effects of scattering and absorption. Linear or nonlinear relationships between aerosol optical depth ( τ a) and have been established to describe the aerosol direct radiative effect on (ADRE). However, considerable uncertainties remain associated with ADRE due to the incorrect estimation of ( τ a in the absence of aerosols). Based on data from the Aerosol Robotic Network, the effects of τ a, water vapor content ( w ) and the cosine of the solar zenith angle ( μ ) on are thoroughly considered, leading to an effective parameterization of as a nonlinear function of these three quantities. The parameterization is proven able to estimate with a mean bias error of 0.32 W m−2, which is one order of magnitude smaller than that derived using earlier linear or nonlinear functions. Applications of this new parameterization to estimate τ a from , or vice versa, show that the root-mean-square errors were 0.08 and 10.0 Wm−2, respectively. Therefore, this study establishes a straightforward method to derive from τ a or estimate τ a from measurements if water vapor measurements are available.
