Aerosol Optical Thickness over the Oceans Derived from GMS-5 during Spring 2002 and 2003

Abstract

Daily and monthly aerosol optical thickness (AOT) over the ocean, derived from the Geostationary Meteorological Satellite (GMS-5) visible data, were compared with those determined from the sun photometer measurements in March and Apri1 2002. Time variations in the daily AOT derived from the GMS-5 showed good agreements with those from the sun photometer measurements. Correlation coefficient between the GMS-5 and the sun photometer derived daily AOTs was 0.85 for 61 samples taken at three sun photometer observation sites; Ryori, Yonagunijima, and Minamitorishima in Japan. The difference of monthly AOT, the GMS-5 minus the sun photometer, in March and April 2002 were −0.03 and 0.03 at Ryori, −0.01 and 0.18 at Yonagunijima, and 0.01 and 0.07 at Minamitorishima, respectively.Monthly regional AOT, defined as the median of the daily AOTs over 30° latitude × 30° longitude region, was calculated in latitude from 60°N to 60°S and in longitude from 80°E to 160°W for March and Apri1 of 2002 and 2003. In the southern hemisphere, monthly regional AOT was less than 0.1; about 0.1∼0.2 in 0°N∼30°N; larger than 0.2 in 30°N∼60°N with a maximum of 0.4∼0.5 in the western region near the Asian continent. AOTs in 2003 were generally smaller than those in 2002 in six regions between 110°E and 160°W of the northern hemisphere, where aerosol loading is most likely affected by the Asian dust. The numbers of regions, in which the AOT increased/decreased/equivalent from 2002 to 2003, were 3/8/1 in March and April, with the AOT changes from 2002 to 2003 to be as large as −0.04∼0.03.