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Ann. Geophys., 22, 1903-1915, 2004
www.ann-geophys.net/22/1903/2004/
© European Geosciences Union 2004
Quality assessment of ground-based microwave measurements of chlorine monoxide, ozone, and nitrogen dioxide from the NDSC radiometer at the Plateau de Bure
P. Ricaud1, P. Baron2, and J. de La Noë1
1Observatoire Aquitain des Sciences de l’Univers (OASU), Laboratoire d’Astrodynamique, d’Astrophysique et d’Aéronomie de Bordeaux (L3AB), CNRS/INSU, Floirac, France
2Noveltis, Toulouse, France
Abstract. A ground-based microwave radiometer dedicated to chlorine monoxide (ClO)
measurements around 278GHz has been in operation from December 1993-June 1996 at
the Plateau de Bure, France (45° N, 5.9° E, 2500m altitude). It
belongs to the international Network for the Detection of Stratospheric Change.
A detailed study of both measurements and retrieval
schemes has been undertaken. Although dedicated to the measurements
of ClO, simultaneous profiles of O3, ClO and
NO2, together with information about the instrumental baseline,
have been retrieved using the optimal estimation method. The vertical
profiles have been
compared with other ground-based microwave data, satellite-borne data and model results.
Data quality shows: 1) the weak sensitivity of the instrument
that obliges to make time averages over several hours; 2) the site location
where measurements of good opacities are possible for only a few days per
year; 3) the baseline undulation affecting all the spectra, an issue common to
all the microwave instruments; 4) the slow drift of some components
affecting frequencies by 3-4MHz within a couple of months. Nevertheless,
when temporally averaging data over a few days, ClO temporal variations
(diurnal and over several weeks in winter 1995) from 35-50km
are consistent with
model results and satellite data, particularly at the peak altitude around
40km,
although temporal coincidences are infrequent in winter 1995. In addition
to ClO, it is possible to obtain O3 information from 30-60km whilst the instrument is not optimized at all
for this molecule. Retrievals of O3 are reasonable when
compared with model and another ground-based data set, although the
lowermost layers are affected by the contamination of baseline remnants.
Monthly-averaged diurnal variations of NO2 are detected at 40km
and appear in agreement with photochemical model results and
satellite zonally-averaged data, although the amplitude is weaker
than the other data sets. This NO2 result highlights the great potential of the
retrieval scheme used.
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