抄録
The imageries of the volcanic eruption clouds (VECs) from Mt. Pinatubo, Philippines were taken at one hour intervals from 2240 ut (universal time) 14 June-2040 ut 15 June, 1991 by the Japanese Geostationary Meteorological Satellite Himawari 4 (GMS-4). These imageries were studied and indicated the following features.
A disc-shaped VEC which is characterized by a visible gray area appeared in the vicinity of Mt. Pinatubo and covered an area ≈130 km in diameter in the visible image taken at 2240 ut on June 14, 1991. The VEC cast shadows on the surrounding white cloud (altitude : ≈16 km) due to typhoon and the VEC's equivalent blackbody temperature (Tbb) based on infrared digital image data was several degrees higher than the tropopause temperature (-83°C), thereby it is believed that the VEC injected into the stratosphere. The formation and dispersion of VECs repeatedly appeared in all visible imageries from 2240 ut 14 June-0540 ut 15 June, 1991. A gigantic disc-shaped VEC appeared, having its center ≈20 km west of the volcano in the 0640 ut visible image and covered an area ≈300 km in diameter. The VEC's Tbb was more than 10°C greater than the tropopause temperature. From 0640 - 0840 ut the VEC radially expanded against an easterly wind, spread out an area ≈600 km in diameter, especially 200 km upwind from the volcano and showed an increase in the VEC's Tbb. Furthermore, the area having a Tbb higher than -60°C continued to expand in all directions, especially up to 100 km upwind until 1140 ut, thus indicating that the volcano's activity continued. At 1240 ut the east edge of the VEC began to move westward, but the VEC continued to extend in the southward and westward directions until 1540 ut. Subsequently, the VEC's Tbb surrounding the volcano rapidly decreased and also the area having a temperature than -70°C further decreased, while the VEC enclosed by the -70°C isotherm gradually changed to the fan-shaped pattern which is dispersing westward from the volcano.
