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Ann. Geophys., 20, 847-862, 2002
www.ann-geophys.net/20/847/2002/
© European Geosciences Union 2002
STRATAQ: A three-dimensional Chemical Transport Model of the stratosphere
B. Grassi, G. Redaelli, and G. Visconti
Universita degli Studi di l’Aquila, Dipartimento di Fisica, Via Vetoio, 67010 Loc. Coppito l’Aquila, Italy
Correspondence to: B. Grassi
(Barbara.grassi@aquila.infn.it)
Abstract. A three-dimensional (3-D)
Chemical Transport Model (CTM) of the stratosphere has been developed and used
for a test study of the evolution of chemical species in the arctic lower
stratosphere during winter 1996/97. This particular winter has been chosen for
testing the model’s capabilities for its remarkable dynamical situation (very
cold and strong polar vortex) along with the availability of sparse chlorine,
HNO3 and O3 data, showing also very low O3
values in late March/April. Due to those unusual features, the winter 1996/97
can be considered an excellent example of the impact of both dynamics and
heterogeneous reactions on the chemistry of the stratosphere. Model integration
has been performed from January to March 1997 and the resulting long-lived and
short-lived tracer fields compared with available measurements. The model
includes a detailed gas phase chemical scheme and a parameterization of the
heterogeneous reactions occurring on liquid aerosol and polar stratospheric
cloud (PSC) surfaces. The transport is calculated using a semi-lagrangian flux
scheme, forced by meteorological analyses. In such form, the STRATAQ CTM model
is suitable for short-term integrations to study transport and chemical
evolution related to "real" meteorological situations. Model
simulation during the chosen winter shows intense PSC formation, with
noticeable local HNO3 capture by PSCs, and the activation of vortex
air leading to chlorine production and subsequent O3 destruction.
The resulting model fields show generally good agreement with satellite data
(MLS and TOMS), although the available observations, due to their limited
number and time/space sparse nature, are not enough to effectively constraint
the model. In particular, the model seems to perform well in reproducing the
rapid processing of air inside the polar vortex on PSC converting reservoir
species in active chlorine. In addition, it satisfactorily reproduces the
morphology of the continuous O3 decline as shown by the satellite
during the investigated period, with a tendency, however, to underestimate the
total column values inside the polar vortex during late winter. As possible
causes of this model/observation difference we suggest an incorrect estimation
of the vertical transport and of the tropospheric contribution.
Key words. Atmospheric composition
and structure (Middle atmosphere-composition and chemistry) Meterology and
atmospheric dynamics (middle atmosphere dynamics)
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