H. K. Roscoe
Lack of trend in Brewer-Dobson circulation, inferred from measurements
of stratospheric NO2 in polar summer
Changes in the speed of the Brewer-Dobson circulation can be deduced
from changes in stratospheric NOy, as it is produced by photo-oxidation
of N2O from the troposphere. We analyse our NO2 measurements from 1990
to 2007 in Antarctica, and use a chemical model to deduce the NOy
from the observed NO2 in midsummer, when the effect of stratospheric
aerosol on NO2/NOy is smallest. The midsummer NOy has large inter-annual
variability and a broad maximum in 2000-2001, but little overall trend.
From our simple model of B-D circulation, the NOy implies similar changes
in speed of circulation but of opposite sign - a broad minimum near 2000.
Regression shows significant correlation with solar and QBO indices,
and there remains a large unexplained cycle of period >17 years.
The trend is +1.4 +/-3.5 %/decade.
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