The direct effect of aerosols on solar radiation based on satellite observations, reanalysis datasets, and spectral aerosol optical properties from Global Aerosol Data Set (GADS)

[摘要] A global estimate of the seasonal direct radiative effect (DRE) of naturalplus anthropogenic aerosols on solar radiation under all-sky conditions isobtained by combining satellite measurements and reanalysis data with aspectral radiative transfer model and spectral aerosol optical propertiestaken from the Global Aerosol Data Set (GADS). The estimates are obtainedwith detailed spectral model computations separating the ultraviolet (UV),visible and near-infrared wavelengths. The global distribution of spectralaerosol optical properties was taken from GADS whereas data for clouds,water vapour, ozone, carbon dioxide, methane and surface albedo were takenfrom various satellite and reanalysis datasets. Using these aerosolproperties and other related variables, we generate climatological (for the12-year period 1984–1995) monthly mean aerosol DREs. The global annual meanDRE on the outgoing SW radiation at the top of atmosphere (TOA, ΔF_TOA)is −1.62 W m⁻² (with a range of −15 to 10 W m⁻²,negative values corresponding to planetary cooling), the effect on theatmospheric absorption of SW radiation (ΔF_atmab) is 1.6 W m⁻²(values up to 35 W m⁻², corresponding to atmospheric warming),and the effect on the surface downward and absorbed SW radiation (ΔF_surf,and ΔF_surfnet, respectively) is −3.93 and −3.22 W m⁻²(values up to −45 and −35 W m⁻², respectively, correspondingto surface cooling). According to our results, aerosols decrease/increasethe planetary albedo by −3 to 13% at the local scale, whereas onplanetary scale the result is an increase of 1.5%. Aerosols can warmlocally the atmosphere by up to 0.98 K day⁻¹, whereas they can cool theEarth's surface by up to −2.9 K day⁻¹. Both these effects, which cansignificantly modify atmospheric dynamics and the hydrological cycle, canproduce significant planetary cooling on a regional scale, althoughplanetary warming can arise over highly reflecting surfaces. The aerosol DREat the Earth's surface compared to TOA can be up to 15 times larger at thelocal scale. The largest aerosol DRE takes place in the northern hemisphereboth at the surface and the atmosphere, arising mainly at ultraviolet andvisible wavelengths.

[学科分类] 大气科学