Volcanic plumes at Miyakejima observed from satellites and from the ground

The eruption of Miyakejima volcano started on 8 July 2000. As of September 2002, SO2 emissions measured by COSPEC average 11000 t/day. As the volcanic gas tends to behave together with the plume, we may infer the advection of the gas from the observation of the plume. Ground observations have been performed from Mikurajima using CCD cameras since September 2000. These pictures clarify the vertical structure of volcanic clouds. The horizontal dispersion of the clouds is well shown in NOAA/AVHRR, Terra/MODIS and other satellite images. Ash-rich clouds at the first stage are well detected by the difference image of NOAA/AVHRR 5 and 4, while vapor-rich clouds are insensitive to the difference. Instead, the latter are detected by the difference of AVHRR 1 and 2, and discriminated well from meteorological clouds in many cases. MODIS data is sensitive to the ash and sulfates of Miyakejima plumes in the 8.6 mm channel, and can detect the fine structure of the plumes with its high-resolution visible channels. Miyakejima plumes contain large quantities of volcanic gases, and their daily monitoring using satellites and ground observations in conjunction with upper wind data helps to understand high concentration events of sulfur dioxide downstream from the volcano.