1. Retrieval of desert dust aerosols vertical profiles from IASI measurements in the TIR atmospheric window Sophie Vandenbussche, Svetlana Kochenova, Ann-Carine Vandaele, Nicolas Kumps, Martine De Mazière With thanks to Robert Spurr for fruitful RT discussions

2. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Introduction Desert dust is one of the major types of aerosols in the atmosphere, responsible for direct climate forcing: absorbtion, scattering and emission indirect forcing through interactions with clouds Health issues when close to the surface

3. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Introduction (continued) Aerosols data are needed not only at Visible wavelengths but also in the Thermal Infrared: No direct relation between measurements at VIS and TIR wavelengths (for ex. different sensitivity to particle size) High transmittance window, high impact of aerosols Day and night measurements Retrieval possible over bright surfaces (deserts)

4. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Introduction (continued) Current dust retrievals in TIR provide a total column (or optical depth) and sometimes an « equivalent » or « radiative » altitude (one layer of the atm. model) (Pierangelo et al, 2004; Peyridieu et al, 2010; DeSouza-Machado et al, 2010) Direct effects probably reasonably represented No information on the « real » vertical distribution of dust → impact on clouds (or health)?? Modellers would benefit from having « real » profile data for comparisons with the output of their emission and transport models

5. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Challenges… Refractive index? Particle size distribution? Altitude of aerosols: low sensitivity…

6. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Retrieval strategy IASI TIR measurements Clouds <10% Reasonable H 2 O profile Signature of dust GEISA Massie dust refractive index; Log-normal size distr. (r=0.6µm  =2µm) GEISA Massie dust refractive index; Log-normal size distr. (r=0.6µm  =2µm) Rodgers OEM retrieval (ASIMUT + LIDORT) 900-930cm -1 & 1095-1125cm -1 Rodgers OEM retrieval (ASIMUT + LIDORT) 900-930cm -1 & 1095-1125cm -1 Compute an average spectrum Max 100km, 6h reduce noise improve altitude sensitivity Compute an average spectrum Max 100km, 6h reduce noise improve altitude sensitivity A priori: 50part/cm3 (0-5km alt) Sa: 100% + Gaussian correlation 1km Profile retrieval Aerosol profile, total column and OD at 10µm Averaging kernels → 2 pieces of information 6 points profile A priori: Sa: 10% Column Surface T

7. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Test-case 22 June 2009 Large plume off the West Coast of the Sahara, seen by MODIS/Terra Over the Ocean… NASA Comparisons of IASI results (10h30 – 22h30) with MODIS (Terra) - 10h30 CALIOP (CALIPSO) - 13h30 – 01h30

8. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Results over the ocean CALIOP extinction coeff at 1.064µm NIGHT

9. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Results over the ocean

10. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Results over the ocean OD « general pattern » looks reasonable with respect to MODIS data OD absolute would require comparisons with other retrievals in the TIR for confirmation General profile shape looks alright in most of the cases (considering that there are only 2 degrees of freedom for the profile retrieval); not so good in the 2-layer cases

11. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Results over the desert - preliminary

12. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Results over the desert - preliminary Exactly same strategy as over the ocean (except: surface emissivity from Zhou et al, 2011) Quite a few retrievals do not converge Need OD comparison data General profile shape looks quite alright again

13. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Conclusions We have developed a strategy to retrieve dust aerosol vertical profiles (+ AKs) from IASI TIR measurements works both over ocean and desert (preliminary) vertical profiles are reasonable w.r.t. CALIOP 2 degrees of freedom OD at 10µm reasonable w.r.t. MODIS OD at 550nm More OD comparisons needed including with other TIR retrievals

14. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Perspectives Attempts to retrieve particle size Attempts to quantify uncertainties, to test the retrieval’s robustness Use other refractive indices and compare Retrieval of refractive index (with constraints)?

15. Thank you!

16. S. Vandenbussche - STCE Workshop: Retrieval of aerosol properties – 24 May 2012 Additional information on data sources Atmospheric profiles – AFGL 1986 tropical atmosphere – Clouds, H2O, T and p from IASI level2 – Surface T from ECMWF operational reanalyses – Sea emissivity: Newman et al, 2005 – Land emissivity: Zhou et al, 2011 – HITRAN 2008 line parameters and cross-sections MODIS (Terra) data: Aerosol Cloud Daily l3 Global v5.1 CALIOP data: Cloud & Aerosol Profile level 2 v 3.01, provisional