The Meteorological Research Institute (MRI) has established a ground-based radiation observation network with facilities in Tsukuba, Fukuoka, Miyakojima, and Minamitorishima, Japan, in order to assess the effects of aerosols and clouds on the surface radiation budget. One of the key instruments of the MRI ground-based radiation observation sites is the POM-02 sky radiometer manufactured by PREDE Co., Ltd., Japan. In order to maintain accuracy in observation by sky radiometer, the reference sky radiometer is calibrated at Mauna Loa Observatory (MLO) of the National Oceanic and Atmospheric Administration (NOAA). The calibration constant of the reference sky radiometer is determined using the Langley plot technique. The accuracy of the sky radiometer observation at each site is maintained by side-by-side intercomparisons among the reference sky radiometer and the other MRI sky radiometers.
Haze was observed in the Kyushu and Okinawa areas in early August 2020. In Fukuoka, haze was observed from the afternoon of August 2 to midnight on August 5 and from the afternoon of August 6 to the afternoon of August 7. In Miyakojima, haze was observed on the afternoon of August 5. At the same time, a satellite tropospheric monitoring instrument (TROPOMI) observed the diffusion and transport of SO2 from Nishinoshima in the Kyushu and Okinawa areas. Sky radiometer observations at Miyakojima on August 5 and at Fukuoka on August 6 showed that the daily mean values of aerosol optical depth at 500 nm AOD(500) were 1.400 and 1.597, respectively, and those of single scattering albedo at 500 nm SSA(500) were 0.994 and 0.992. The Ångström exponent α was 1.056 and 1.181, respectively. The volume size distribution retrieved from the sky radiometers showed modes around radii 0.2 μm and 2.0 μm, which are related to sulfate and volcanic ash. These results are consistent with electron micrographs and the elemental analysis results of sampled aerosol particles in Fukuoka.
