SCIAMACHY CO over land and oceans: 2003–2007 interannual variability 1SRON Netherlands Institute for Space Research, Utrecht, The Netherlands
2Royal Netherlands Meteorological Institute (KNMI), de Bilt, The Netherlands
3Faculty of Earth and Life Sciences, VU University, Amsterdam, The Netherlands
Received: 24 December 2008 – Published in Atmos. Chem. Phys. Discuss.: 02 March 2009 Abstract. We present a new method to obtain accurate
SCIAMACHY CO columns over clouded ocean scenes. Based on an improved version of the
Iterative Maximum Likelihood Method (IMLM) retrieval algorithm, we now have retrieved
five years of data over both land and clouded ocean scenes
between 2003 and 2007. The ocean-cloud method uses
the CH4 columns retrieved simultaneously with
the CO columns to determine the cloud top height.
The CH4 cloud top height is in good agreement
with the FRESCO+ cloud
top height determined from UV-VIS oxygen-A band measurements, providing confidence
that the CH4 cloud top height is a good diagnostic of
the cloud top height over (partially) clouded ocean scenes.
The CO measurements over clouded ocean scenes have been compared
with collocated modeled CO columns over the same clouds and agree well.
Using clouded ocean scenes quadruples the number of useful CO measurements compared to land-only
Revised: 23 May 2009 – Accepted: 27 May 2009 – Published: 11 June 2009
The five-year CO data set over land and clouded ocean scenes presented here
is based on an improved version of the IMLM algorithm which includes a more
accurate determination of the random instrument-noise error for CO. This
leads to a smaller spread in the differences between single CO measurements
and the corresponding model values. The new version, IMLM version 7.4, also
uses updated spectroscopic parameters for H2O and CH4 but this has only
a minor impact on the retrieved CO columns. The five-year data set shows
significant interannual variability over land and over clouded ocean scenes.
Three examples are highlighted: the Asian outflow of pollution over the
northern Pacific, the biomass-burning outflow over the Indian Ocean
originating from Indonesia, and biomass burning in Brazil. In general there
is good agreement between observed and modeled seasonal cycles and
Citation: Gloudemans, A. M. S., de Laat, A. T. J., Schrijver, H., Aben, I., Meirink, J. F., and van der Werf, G. R.: SCIAMACHY CO over land and oceans: 2003–2007 interannual variability, Atmos. Chem. Phys., 9, 3799-3813, doi:10.5194/acp-9-3799-2009, 2009.