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Implications of upper stratospheric trace constituent changes observed by HALOE for O 3 and ClO from 1992 to 1995
Author(s) -
Siskind David E.,
Froidevaux L.,
Russell J. M.,
Lean J.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/98gl02664
Subject(s) - microwave limb sounder , stratosphere , atmospheric sciences , halogen , occultation , flux (metallurgy) , trace gas , chlorine , solar cycle , environmental science , chemistry , physics , astrophysics , alkyl , organic chemistry , quantum mechanics , magnetic field , solar wind
Measurements from the Halogen Occultation Experiment (HALOE) of the upper stratosphere show increases in HCl and H 2 O and decreases in CH 4 and O 3 during the period 1992–1995. These changes all coincide with the decline of solar cycle 22. Using a simple photochemical model, we find that 4 major components contribute to the O 3 decrease: 1) an increase in total chlorine as indicated by increasing HCl 2) an additional increase in reactive chlorine due to repartitioning of Cly by the decreasing CH 4 3) a decrease in odd oxygen production due to decreased solar flux and 4) an increase in odd hydrogen loss due to increasing H 2 O. At 2 mbar, the Cly repartitioning is the largest cause of O 3 changes. Because the Cly repartitioning coincides with decreasing solar flux, some recent observational estimates of the long‐term response of upper stratospheric O 3 to solar UV irradiance variability may be too large. Compared with the HALOE O 3 data, the model O 3 exhibits a larger negative trend. This appears to be because the model O 3 is more sensitive to the increased H 2 O than is the observed O 3 . The 20–30% decline in CH 4 also implies a large increase in ClO which exceeds that expected from CFCs. Observations of ClO from the Microwave Limb Sounder (MLS) support this inference.