| Aerosol has much impact on the radiation through direct and indirect ways, andplays a crucial role on Earth’s climate system. Aerosol in Qingdao, a coastal city, isaffected both by land and ocean. Study on the aerosol radiative forcing in Qingdao isvery important to understand the effects of aerosol on climate in coastal area. Usinglong-term ground-based aerosol optical and solar irradiance data, the impact ofaerosol and water vapor on solar radiation is analyzed in this paper. Firstly, the diurnaland seasonal variation of aerosol optical depth (AOD) and single scattering albedo(SSA) are discussed. SBDART model is used to calculate the surface radiation underclear sky with the radiosonde data and standard atmospheric profile as parametricinput respectively, then comparisons between measured and modeled irradiance aremade to analyze the calculation error. The radiative forcing of aerosol and water vaporare simulated at the surface and the top of the atmosphere respectively, and the effectsof aerosol on the atmosphere is discussed.(1) The diurnal variations of AOD under clear sky display five types: raising,reducing, higher at noon, lower at noon and oscillation. The seasonal mean AOD ishighest in summer (0.79), lower in spring (0.63), lowest in autumn (0.49) and winter(0.41). South wind increases AOD. AOD has obvious positive correlation withtemperature and pressure.The diurnal variations of SSA under clear sky show four types, which areraising type, lower at noon, reducing type, and oscillation type. The variations of SSAhave little difference among different seasons. The SSA is correlated with the relativehumidity in summer, autumn, and winter.(2) Sensitivity tests indicate that the AOD and water vapor are sensitive to thecalculated surface radiation. The value calculated with standard atmospheric profile islower than measured irradiance, and the mean bias error is higher than50W/m2. Thevalue calculated with radiosonde date is improved with a mean bias error of10W/m2(visible band). The difference of modeled irradiance using radiosonde date from themodeled irradiance using model atmosphere at different bands indicates that thehigher error is due to the uncertainty of water vapor. The results in visible band arebetter than infrared band, and the mean bias error are11W/m2and33W/m2respectively. The results in visible and infrared band are both directly correlated to themeasured irradiance.(3) The impact of aerosol on radiation is concentrated in visible band while theaerosol radiative forcing is very small in infrared band. In visible band, aerosolssignificantly affect the radiation budget. The radiative forcing of aerosol leads to astrong cooling effect at the surface and a warming effect in the atmosphere. Theaerosol radiative forcing at the surface and the top of the atmosphere are-58W/m2and-10W/m2, and the radiative forcing in the atmosphere is47W/m2which lead to aheating rate of0.47K/d.The radiative forcing at the surface and in the atmosphere is directly correlated to AOD, and the correlations are-0.916、0.798respectively. In contrast the correlationbetween the radiative forcing at the top of atmosphere and AOD is less obvious.All the surface aerosol radiative forcing is negative while the sign of the radiativeforcing at the top or in the atmosphere is correlated to SSA. There is positive radiativeforcing at the top of the atmosphere only when the SSA is less than0.9. And there isnegative radiative forcing in the atmosphere when the SSA is close to1.(4) In infrared band the radiative forcing of aerosol is lower than water vapor.Water vapor plays an absorption effect on longwave radiation, and the radiativeforcing at the surface and the top of atmosphere are89W/m2、4W/m2respectively. |
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