WP 5 : Clouds & Aerosols

1. WP 5 : Clouds & Aerosols Absorbing Aerosol Index (AAI) L.G. Tilstra and P. Stammes Royal Netherlands Meteorological Institute (KNMI) SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

2. Quality of the official SCIAMACHY Absorbing Aerosol Index (AAI) level-2 product SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

3. Absorbing Aerosol Index: version 3.01 versus version 5.02W Changes in L1–2 data processor: • Totally new algorithm setup • New look-up tables (pseudo spherical atmosphere + including polarisation) • Better surface height database • ...  version 5.02W is a huge improvement on version 3.01 SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

4. Scientific product SC-AAI versus L2-AAI v5.02W (2003) Scientific product (SC-AAI) (grey = sun glint filtering) Official product (L2-AAI v5.02W) SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

5. Scientific product SC-AAI versus L2-AAI v5.02W (2003) Scatter plot: Explanation for the differences: • Calibration correction SC-AAI • Degradation correction SC-AAI • Ozone dependence taken into account in SC-AAI • L2-AAI: measurements “converted” to the (shorter) integration time of cluster 26 (O2–A band) Good agreement (in the year 2003) SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

6. Scientific product SC-AAI versus L2-AAI v5.02W (2011) Scientific product (SC-AAI) Official product (L2-AAI)  The official L2-AAI is suffering from a scan-angle dependence SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

7. Scientific product SC-AAI versus L2-AAI v5.02W (2011) Scatter plot: colours: scan mirror positions Official product suffers from a strong scan-angle dependence in 2011 SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

8. Influence of (scan-angle dependent) instrument degradation: Global mean reflectance [no m-factors applied] Global mean residue (AAI) [Tilstra et al., JGR 117, 2012] SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

9. M-factors applied in calculation of L2-AAI: Global mean residue (AAI) Current m-factor approach is scan-angle independent; the official L2-AAI product therefore shows a scan-angle dependence. Although v5.02W is a large improvement on the previous version, data after 2006 are not to be used without application of necessary corrections by the user. SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

10. Conclusions: • The official AAI product of level-2 version 5.02W is a large improvement w.r.t. the previous version 3.01. • Instrument degradation has a large impact on the residue. The use of the official AAI product after 2006 is problematic. • This is, however, a level-1 issue. • This issue will be addressed in version 8.x of the level-1 product. SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

11. Extra slides SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

12. Introduction: Absorbing Aerosol Index (AAI) The AAI represents the scene colour in the UV • Definition of the residue: where the surface albedo A for the simulations is such that: (A is assumed to be wavelength independent: A340 = A380) no clouds, no aerosols : r = 0 clouds, scattering aerosols : r < 0 absorbing aerosols : r > 0 B. Definition of the AAI: AAI = residue > 0 (and the AAI is not defined where residue < 0) The AAI can be retrieved over land and sea surfaces, even in the presence of clouds. SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

13. Example of global aerosol distribution recorded by SCIAMACHY: The “Global Dust Belt”: Desert Dust Aerosols (DDA) (dust storms, all year) Biomass Burning Aerosols (BBA) (dry season, anthropogenic) AAI from other UV satellite instruments: TOMS, GOME-1, OMI, GOME-2. Combined with SCIAMACHY there are more than three decades (1978–2012) of AAI data available for studies of trends in desert dust and biomass burning aerosol. SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

14. The “Global Dust Belt” SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013

15. AAI products from GOME-1, SCIAMACHY, GOME-2, and OMI: *GOME-1: loss of global coverage on 22 June 2003 ; instrument retired on 4 July 2011 SCIAvisie Meeting, KNMI, De Bilt, 08-02-2013