In tropical regions, said atmospheric scientist Brian Toon, "green suns and blue moons are probably being seen now" because of the volcanic plume being carried by stratospheric winds.; In the fall, throughout the Northern Hemisphere, "it will be extremely obvious to the ordinary person. At sunrise and sunset, the horizon will have a glowing purplish color."; Drivers heading toward the sun will see extra-intense glare. And airliners' windows may be etched by acid, as happened after the 1982 eruption of Mexico's El Chichon volcano, said Toon, of the National Aeronautics and Space Administration's Ames Research Center in Mountain View. Sulfuric acid in the air comes from huge amounts of sulfur dioxide released by the volcano.; Last month's eruption of Mount Pinatubo produced a massive cloud of dust, sulfur dioxide and other gases that rose into the stratosphere, reaching altitudes between 80,000 and 120,000 feet. The plume is at least twice as large as El Chichon's, Toon said, and probably will remain aloft for years.; Jim Lynch, of the National Oceanic and Atmospheric Administration, is tracking the plume using instruments aboard the Nimbus-7 satellite. He said, "All indications are that this eruption has exceeded El Chichon by two or three times."; Toon said that in the past 80 years, there have been only three volcanic eruptions that might have global climatic impact -- El Chichon in Mexico; Agung, which erupted in Bali in 1963; and Pinatubo.; The cloud now covers a zone 30 degrees north and 30 degrees south of the equator, so almost 50 percent of the globe is blanketed.; "We're expecting it to stay around for about five years. With time it will spread north and south from where it is," Lynch said.; Whether climatic cooling will result from Pinatubo's eruption is not known, scientists said. El Chichon may have caused a fraction of a degree of global cooling, but researchers are still unsure. El Chichon's eruption coincided with an El Nino climatic event, which may have reversed or accentuated the volcanic effects. Another El Nino seems to have started recently, scientists said.; An El Nino event -- which involves periodic warming of the Pacific Ocean's surface waters -- can severely disturb normal climate.
The cloud of dust and gases from Mt. Pinatubo 's eruption last month , over twice the size of Mexico 's El Chichon in 1982 , rose into the stratosphere and covers 50 % of the globe . Sulfur contained in the plume becomes sulfuric acid and etches airliner windows . The plume may remain aloft for many years and is tracked by satellite . Suns appear green and moons blue in tropical summer , and in northern autumn the horizon will glow purple at sunrise and sunset . In the past 80 years , three events may have had global climatic impact -- El Chichon , observed in Bali in 1963 , and Pinatubo .