2005 Volume 83A Pages 307-313
According to records of meteorological stations of the Japan Meteorological Agency (JMA), the occurrence of Kosa dust events increased during 2000-2002. This was verified by the analyses of aerosol optical depth at 500 nm (τ500) and Ångström exponent (α) obtained on a minutely basis by sun photometers in JMA from 1998 through 2002. The significant aerosol event (τ500 > 0.3) was classified into “a significant large particle event” (α ≤ 1.0) and “a significant small particle event” (α > 1.0). “Significant large particle event days” in Ryori were clearly more frequent from 2000 to 2002 compared with 1998 and 1999, and corresponded with the frequencies of Kosa dust events in China and Japan. In Yonagunijima, Japan, however, “Significant large particle event days” were not corresponded with the frequencies of Kosa dust events in China. Moreover, the occurrence distribution of the Ångström exponent (α), an index of particle size distribution, in Yonagunijima showed that typical Kosa events were rare, while significant small particle events occurred frequently. This indicates the dominant influence of relatively small particles on the large spring aerosol optical depth in Yonagunijima, rather than large particles such as Kosa dust. Trajectory analysis suggested that these small particles originated from urban pollution in the east coast of the Asian continent and Taiwan and/or smoke from biomass burning in Southeast Asia.