Atmospheric Carbon Gases Retrieved from SCIAMACHY by WFM-DOAS: Version 0.5 CO and CH4 and Impact of Calibration Improvements on CO2 Retrieval
The three carbon gases carbon monoxide (CO), carbon dioxide (CO2), and methane
(CH4) are important atmospheric constituents affecting air quality and climate. The
nadir spectra of reflected and scattered solar radiation in the near-infrared region, as
observed by SCIAMACHY/ENVISAT, contain information on the vertical 5 columns of
these gases. A modified DOAS algorithm (WFM–DOAS) has been developed to retrieve
this information. The main SCIAMACHY/WFM–DOAS data products are CO
vertical columns and dry-air column averaged mixing ratios of methane and CO2, denoted
XCH4 and XCO2, respectively. For CO and methane we present new results
10 obtained with an improved version of WFM–DOAS (v0.5). The SCIAMACHY data
products have been compared with global reference data (MOPITT for CO, TM5 model
simulations for XCH4). The comparisons indicate that major problems of the previous
version of WFM–DOAS (v0.4x) related to the varying ice-layer on the SCIAMACHY
channel 8 detector have been solved. On average, the SCIAMACHY CO agrees within
15 10% (standard deviation 30%) with MOPITT but regionally, especially over northern
South America, large differences have been found (up to about 80%). For methane
we present global and regional maps which are compared to TM5 model simulations
performed using standard emission inventories. Overall, there is good agreement but
regionally there are substantial differences, e.g., due to limitations of current methane
20 emission inventories. It still needs to be assessed by how much emission inventories
can be improved by using the SCIAMACHY data. Concerning CO2 we present
a comparison of SCIAMACHY XCO2 (WFM-DOAS v0.4) with TM3 model simulations
over Park Falls, Wisconsin, USA. The peak-to-peak XCO2 variability as measured by
SCIAMACHY (seasonal cycle of year 2003–2005 data) is _13 ppmv, in good agree25
ment with preliminary analysis of ground-based Fourier Transform Spectrometer (FTS)
measurements, which is a factor of 2.3 larger than the XCO2 variability of TM3 model
simulation for 2003. Park Falls is one of the few FTS ground stations which measure
column averaged CO2 and detailed comparison with these measurements (after data
release) will help identifying the reason for the observed differences between SCIAMACHY and global (atmospheric) carbon models such as TM3 as reported here and
in previous studies. For all three carbon gases we present regional results including
seasonal variation focusing on China.
DE BEEK Ruediger;
BUCHWITZ Michael;
NOEL Stefan;
BURROWS John;
BOVENSMANN Heinrich;
BRUNS M.;
BREMER Holger;
BERGAMASCHI Peter;
KOERNER Stefan;
HEIMANN Martin;
SCHNEISING O.;
KHLYSTOVA I.;
2006-02-20
EUROPEAN GEOSCIENCES UNION
JRC32688
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