Interannual changes in stratospheric constituents and global circulation derived from satellite data

The characteristics of low-frequency interannual changes in stratospheric constituents are examined using measurements from the HALOE [1991-1999] and SAGE II [1984-1998] satellite instruments. Both the increasing H 2 O and decreasing CH4 observations from the first several years of HALOE measurements are found to be absent (or partially reversed) in the data since ∼ 1996. Ozone and NO x (NO + NO 2 ) observations from HALOE also show trends' over ∼ 1991-1995 that become flat in the latter record. Comparisons with the longer-term SAGE II measurements of ozone and NO 2 demonstrate that changes over the short period 1991-1995 are not representative of decadal-scale trends, but rather are episodic in nature. One possibility is that these changes reflect a prolonged response to the Mt. Pinatubo volcanic eruption in 1991. Stratospheric temperatures and derived circulation statistics are examined for the period 1979-1999. While Pinatubo produced enhanced tropical upwelling in the stratosphere for 1-2 years, other sources of stratospheric variability probably also contribute to low-frequency constituent trends.