Evaluation of tropospheric ozone columns derived from assimilated GOME ozone profile observations Royal Netherlands Metrological Institute (KNM), P.O. Box 201, 3730 AE, de Bilt, the Netherlands
Received: 27 Feb 2009 – Published in Atmos. Chem. Phys. Discuss.: 13 May 2009 Abstract. Tropospheric O3 column estimates are produced and evaluated from
spaceborne O3 observations by the subtraction of assimilated O3
profile observations from total column observations, the so-called
Tropospheric O3 ReAnalysis or TORA method. Here we apply the TORA
method to six years (1996–2001) of ERS-2 GOME/TOMS total O3 and ERS-2
GOME O3 profile observations using the TM5 global chemistry-transport
model with a linearized O3 photochemistry parameterization scheme.
Revised: 23 Sep 2009 – Accepted: 13 Oct 2009 – Published: 28 Oct 2009
Free running TM5 simulations show good agreement with O3 sonde observations
in the upper-tropospheric and lower stratospheric region (UTLS), both for short
day-to-day variability as well as for monthly means. The assimilation of
GOME O3 profile observations counteracts the mid-latitude stratospheric
O3 drift caused by the overstrong stratospheric meridional circulation
in TM5. Assimilation of GOME O3 profile observations also improves the
bias and correlations in the tropical UTLS region but slightly degrades the
model-to-sonde correlations and bias of extra-tropical UTLS. We suggest that
this degradation is related to the large ground pixel size of the GOME
O3 measurements (960×100 km) in combination with retrieval and
calibration errors. The added value of the assimilation of GOME O3
profiles compared to stand-alone model simulations lays in the long term
variations of stratospheric O3, not in short term synoptic variations.
The evaluation of daily and monthly tropospheric O3 columns obtained
from total column observations and using the TORA methodology shows that the
use of GOME UV-VIS nadir O3 profiles in combination with the spatial
resolution of the model does not result in satisfactory residual
tropospheric ozone columns.
Citation: de Laat, A. T. J., van der A, R. J., and van Weele, M.: Evaluation of tropospheric ozone columns derived from assimilated GOME ozone profile observations, Atmos. Chem. Phys., 9, 8105-8120, doi:10.5194/acp-9-8105-2009, 2009.