4D-Var assimilation of MIPAS chemical observations: ozone and nitrogen dioxide analyses Q. Errera1, F. Daerden1, S. Chabrillat1, J. C. Lambert1, W. A. Lahoz2, S. Viscardy1, S. Bonjean1,*, and D. Fonteyn1,** 1Insitut d'Aéronomie Spatiale de Belgique, BIRA-IASB, Belgium 2Norsk Institutt for Luftforskning, NILU, Norway *now at: Sputnik Web, Belgium **now at: Belgian Federal Science Office, Belgium
Abstract. This paper discusses the global analyses of stratospheric ozone (O3) and
nitrogen dioxide (NO2) obtained by the Belgian Assimilation System for
Chemical Observations from Envisat (BASCOE). Based on a chemistry transport
model (CTM) and the 4-dimensional variational (4D-Var) method, BASCOE has
assimilated chemical observations of O3, NO2, HNO3, N2O, CH4
and H2O, made between July 2002 and March 2004 by the Michelson
Interferometer for Passive Atmospheric Sounding (MIPAS) onboard the European
Space Agency (ESA) Environment Satellite (ENVISAT). This corresponds to the
entire period during which MIPAS was operating at its nominal resolution.
Our analyses are evaluated against assimilated MIPAS data and independent
HALOE (HALogen Occultation Experiment) and POAM-III (Polar Ozone and Aerosol
Measurement) satellite data. A good agreement is generally found between the
analyses and these datasets, in both cases within the estimated error bars of
the observations. The benefit of data assimilation is also evaluated by
comparing a BASCOE free model run with MIPAS observations. For O3, the
gain from the assimilation is significant during ozone hole conditions, and
in the lower stratosphere. Elsewhere, the assimilation does not provide
significant improvement. For NO2, the gain from the assimilation is
realized through most of the stratosphere. Using the BASCOE analyses, we
estimate the differences between MIPAS data and independent data from HALOE
and POAM-III, and find results close to those obtained by classical
validation methods involving only direct measurement-to-measurement
comparisons. Our results extend and reinforce previous MIPAS data validation
efforts by taking into account a much larger variety of atmospheric states
and measurement conditions.
This study discusses possible further developments of the BASCOE data
assimilation system; these concern the horizontal resolution, a better
filtering of NO2 observations, and the photolysis calculation near the lid
of the model. The ozone analyses are part of the PROMOTE project and are
publicly available via the BASCOE website (http://www.bascoe.oma.be/promote/).
Citation: Errera, Q., Daerden, F., Chabrillat, S., Lambert, J. C., Lahoz, W. A., Viscardy, S., Bonjean, S., and Fonteyn, D.: 4D-Var assimilation of MIPAS chemical observations: ozone and nitrogen dioxide analyses, Atmos. Chem. Phys., 8, 6169-6187, doi:10.5194/acp-8-6169-2008, 2008.