Evaluation of SCIAMACHY CO total columns with MOPITT CO and FTIR measurements
Jos De Laat(1), Annemieke Gloudemans(2), Ilse Aben(2) and Hans Schrijver(2)
(1) Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730 AE De Bilt, Netherlands
(2) SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584CA Utrecht, Netherlands
We present a detailed comparison of SCIAMACHY carbon monoxide (CO) total column measurements with MOPITT CO and FTIR measurements for the years 2004 and 2005.
The effect of instrument-noise errors, different sensitivities, collocations and clouds are quantified using model simulated CO profiles. When taking these effects into account, spatio-temporal variations of SCIAMACHY, MOPITT, and FTIR CO total columns are similar. Because of the difference in vertical sensitivity, the short-wave infrared SCIAMACHY observations are complementary to the thermal-infrared MOPITT observations. The agreement of SCIAMACHY and MOPITT observations in the Northern Hemisphere confirms earlier findings that chemistry-transport models underestimate Northern Hemispheric CO due to underestimated anthropogenic emission estimates in South and East Asia. The SCIAMACHY CO total column observations also highlight the unique ability to probe the troposphere down to the surface at short-wave infrared wavelengths, even at (very) high northern latitudes.
At Southern Hemispheric latitudes >45S SCIAMACHY underestimates CO total columns compared to model results. This may be caused by the empirical correction for the SCIAMACHY ice layer. On the other hand, MOPITT shows an overestimation at these latitudes compared to model results, which may be partly caused by too low emissions in de model and partly related to the MOPITT a priori.
In the transition from oceans to dry desert regions, MOPITT shows a rapid increase in the CO column which is not seen in SCIAMACHY CO and TM4 model results. The occurrence of this bias and the agreement between MOPITT and SCIAMACHY over the oceans suggests that this bias may be related to the thermal infrared emissivity of land dry surfaces, but this needs further confirmation.