MULTIWAVELENGTH LIDAR OBSERVATIONS OF THE DECAY PHASE OF THE STRATOSPHERIC AEROSOL LAYER PRODUCED BY THE ERUPTION OF MOUNT-PINATUBO IN JUNE1991

A small three-wavelength (355-, 532-, and 1064-nm) lidar system at NAS A Langley Research Center in Hampton, Virginia, has been used since 19 92 to make measurements on stratospheric aerosols. The data have been processed to study the decay rate of the stratospheric aerosol layer f ormed after the eruption of Mount Pinatubo in 1991 and its modulation, the aerosol effective radius, and the column mass loading. The strato spheric aerosol decay curves show annual and biennial cycles as well a s short-term changes. At 532 nm, the decay time constant was 302 days for the period from February 1992 to August 1994 and had increased to 645 days for the period from September 1994 to December 1997. By 1996 the integrated stratospheric aerosol backscatter had fallen to levels (7.7 X 10(-5) sr(-1) at 532 nm) close to those seen in 1979 and 1989-1 991. This decreasing trend was still continuing in 1997, showing no ev idence for any anthropogenic contribution to the stratospheric aerosol . (C) 1998 Optical Society of America.