TOTAL OZONE TRENDS AT 16 NOAA CMDL AND COOPERATIVE DOBSON SPECTROPHOTOMETER OBSERVATORIES DURING 1979-1996/

Ozone trends, derived from 1979-1996 Dobson spectrophotometer total oz one data obtained at five U.S. mainland midlatitude stations, averaged -3.4, -4.9, -2.6, -1.9, and -3.3%/decade for winter, spring, summer, and autumn months, and on an annual basis, respectively. At the lower latitude stations of Mauna Loa and Samoa, corresponding-period annual ozone trends were -0.4 and -1.3%/decade, respectively, while at Huanca yo, Peru, the 1979-1991 annual trend was -0.9%/decade. A linear trend approximation to ozone changes that occurred since 1978 during austral daylight times at Amundsen-Scott (South Pole) station, Antarctica, yi elded a value of -12%/decade. By combining 1979-1996 annual trend data for three U.S. mainland stations with trends for the sites derived fr om 1963-1978 data, it is estimated that the ozone decrease at U.S. mid latitudes through 1996, relative to ozone present in the mid-1960s, wa s -6.7%. Similar analyses incorporating South Pole data obtained since 1963 yielded an ozone change at South Pole (daylight observations) th rough 1996 of approximately -25%. South Pole October total ozone value s in 1996 were lower than mid-1960s October ozone values by a factor o f two. Trend data are also presented for several shorter record period stations, including the foreign cooperative stations of Haute Provenc e, France; Lauder, New Zealand; and Perth, Australia.