Mid-latitude ozone changes: studies with a 3-D CTM forced by ERA-40 analyses W. Feng1, M. P. Chipperfield1, M. Dorf2, K. Pfeilsticker2, and P. Ricaud3 1Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK 2Institute für Umweltphysik, University of Heidelberg, Heidelberg, Germany 3Laboratoire d'Aerologie, Observatoire Midi-Pyrenees, Toulouse, France
Abstract. We have used an off-line three-dimensional (3-D) chemical
transport model (CTM) to study long-term changes in stratospheric
O3. The model was run from 1977–2004 and forced by ECMWF ERA-40
and operational analyses. Model runs were performed to
examine the impact of increasing halogens and additional
stratospheric bromine from short-lived source gases.
The analyses capture much of the observed interannual variability
in column ozone, but there are also unrealistic features. In
particular the ERA-40 analyses cause a large positive anomaly
in northern hemisphere (NH) column O3 in the late 1980s. Also, the
change from ERA-40 to operational winds at the start of 2002
introduces abrupt changes in some model fields (e.g. temperature,
ozone) which affect
analysis of trends.
The model reproduces the observed column increase in NH mid-latitudes
from the mid 1990s. Analysis of a run with fixed halogens
shows that this increase is not due to
a significant decrease in halogen-induced
loss, i.e. is not an indication of recovery. The model predicts
only a small decrease in halogen-induced loss after 1999.
In the upper stratosphere, despite the modelled turnover of chlorine
around 1999, O3 does not increase because of the effects of increasing
ECMWF temperatures, decreasing modelled CH4 at this
altitude, and abrupt
changes in the SH temperatures at the end of the ERA-40 period.
The impact of an additional 5 pptv stratospheric bromine from short-lived
species decreases mid-latitude column O3 by about 10 DU. However,
the impact on the modelled relative O3 anomaly is generally
small except during periods of large volcanic loading.
Citation: Feng, W., Chipperfield, M. P., Dorf, M., Pfeilsticker, K., and Ricaud, P.: Mid-latitude ozone changes: studies with a 3-D CTM forced by ERA-40 analyses, Atmos. Chem. Phys., 7, 2357-2369, doi:10.5194/acp-7-2357-2007, 2007.