Version 6 Performance and Test Report This section describes the AIRS V6 carbon monoxide (CO) products previously listed, the tests, and the preliminary validation for these products. For testing of the V6 CO product, AIRS dataset from March 4, 2006 is used to compare against in situ measurements obtained by the Differential Absorption Carbon Monoxide Measurements (DACOM) (Sachse et al., 1987), which took place as part of NASA’s Intercontinental Chemical Transport Experiment (INTEX-B) (Singh et al., 2008) field mission. The V6 CO products are further compared with the V5 products to evaluate improvements. The majority of the testing is done for the AIRS/AMSU retrieval using QC = (0,1), but comparisons are also shown with the AIRS IR-only retrievals. The latest V6 version tested to date is V6.0.2.
Carbon Monoxide Trapezoids and A Priori: In AIRS V6 CO, we have adapted the same retrieval layers as in V5, which correspond to 9 trapezoidal functions (McMillan et al., 2011). The major differences for the AIRS CO retrievals between AIRS V5 and V6 are primarily due to the use of the prior information or first guess. Two uniform CO profiles are used for the Northern Hemisphere (NH) and the Southern Hemisphere (SH) separately and they are developed using NCAR global MOZART (Model of Ozone and Related Tracers, Brasseur et al., 1998) monthly mean climatology. The MOZART monthly mean climatology was computed from 2.8x2.8 grid point 3D model outputs from 2002-2009, and interpolated to AIRS spatial and temporal resolution before averaging for each month. We have trimmed off the boundary layer high CO amount from the model outputs by extrapolation from the layers above since AIRS sensitivity does not extend to this layer and the high CO values would be entirely from the model. In addition, we add the Air Force Geophysics Laboratory (AFGL) climatology profile, same as used in V5, from 30 to 2 hPa. Figure 72 shows the monthly variation of the CO climatology profiles used as the first guess profiles for the NH (top) and SH (bottom), respectively.
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