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Transport and radiative impacts of Asian tropospheric aerosols (dust, sulfate, black carbon (BC), organic carbon (OC), and sea salt) during springtime 2001 were simulated using a regional-scale chemic...al transport-radiation model. Model results are intensively examined with the optical observation at the surface monitoring stations. It was shown that modeled aerosol optical thickness (AOT) and Ångströme exponent accurately captured many of the observed characteristics. Analyses for the modeled AOT also showed that Asian aerosol outflows are most dominant at a region between 25°N and 45°N. The aerosol direct radiative forcings at tropopause (ARF) under the clear and all sky conditions were evaluated. It was shown that sulfate has significantly negative forcing, especially under the clear sky, and clear-sky total ARF always indicates negative values due to its negative forcing. We also found that Asian dust is remarkable aerosol under the overcast condition because it has so large positive forcing as to offset negative impacts of other aerosols due to the absorption of the radiation enhanced by the cloud layer. Finally, springtime Asian-scale averaged ARFs under the clear and all sky conditions were evaluated. The clear-sky ARF were -1.45Wm-2 for sulfate, -0.99Wm-2 for OC, -0.39 Wm-2 for dust, -0.24 Wm-2 for sea salt and +0.19Wm-2 for BC, respectively. For the all-sky ARF, it were evaluated as to be -0.74Wm-2 for sulfate, -0.51Wm-2 for OC, -0.16Wm-2 for dust, -0.13Wm-2 for sea salt and +0.26Wm-2 for BC, respectively. These individual negative impacts are very large and a positive forcing of BC is small relatively to the annual global mean ARF reported by past study, respectively. Therefore, we conclude that the Asian aerosol outflow causes a regional cooling effect, and its magnitude is very large compared with their annual global effect.続きを見る
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