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Recent eruptions of Kilauea volcano, the Island of Hawaii, had ejected large amount of volcanic gas into the clean maritime air over the Pacific since March 2008. During the eruptions, large part of t...he fine mode aerosols covering the downwind region can be considered as volcanic sulfate. We analyzed the atmospheric impact of the volcanic sulfate based on the satellite retrievals and a 3-D global chemistry-radiation coupled transport model. We estimated the volcanic SO_2 emission as 3.6 Tg for the year of 2008. Observed aerosol extinction by a satellite significantly increased in the longitudinal range of 155°W ‐ 160°E (about 5000 km downwind of Hawaii) and the vertical range of 1.5 ‐ 3 km in 2008 and 2010 corresponding to an increase in the SO_2 column amount around the Hawaii. We analyzed retrieved aerosol optical depth (AOD) and cloud droplet radius (CDR) by the satellite observation for the high SO_2 periods. For all the seasons, the CDRs decrease with an increase in the AOD and the decreasing rate does not depend on the season. For the same AODs, the CDRs vary with the seasons in a range of 2 µm. The CDR is smallest in wintertime and largest in autumn. This variation is related to the seasonal change of the cloud top pressure in the region. The model result well reproduced the seasonal variation of the relationship between the CDR and AOD. We also estimated radiative forcing of the volcanic sulfate from the Kilauea in 2008 as -0.13 W/m^2, which is one tenth of the global mean anthropogenic aerosol forcing assessed by IPCC (2007).続きを見る
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