 Similar picture from MODIS and MISR aerosol optical depth (AOD)  Both biomass and dust emissions in the Sahel during the winter season  Emissions from the Bodélé depression throughout the year, peaking during the spring season  Change in the latitude of the export with season

 2 x 2.5 resolution with 47 vertical levels  Dust emitted according to Zender et al. [2003]  Dust emitted into four size bins:  0.1–1.0, 1.0–1.8, 1.8–3.0, and 3.0–6.0 µm radius  Optics improved using SHADE size distribution measurements

 AOD decreased by 10-25%  Due to size dependence of scattering  NB no change in total dust mass Original uniform mass partitioning New dust mass partitioning

 The model captures the spatial distribution, magnitude, and the seasonality of the AOD  Statistical comparison with both MISR and MODIS yields R>0.63 over the region shown  AOD at the Bodélé Depression underestimated by the model  Comparison with AERONET also made at eight sites over the three year period

 Seasonality in vertical distribution reproduced well  Missing aerosol close to ocean surface – dust and marine? Marine aerosol? Lapina et al. [2011]

 Annual westward export 250±50Tg (240±80Tg from MODIS 1 )  Deposition to Atlantic is slightly higher than other studies 1,2,3,4  Deposition to the Amazon is lower than previously estimated 1,5 1 Kaufman et al., [2005] 2 Ginoux et al., [2004] 3 Prospero et al., [1996] 4 Fan et al., [2004] 5 Mahowald et al., 2005] Tg AmazonCaribbeanAtlantic DJF3.6±2.50.4± ±24.2 MAM7.5±1.43.1± ±7.3 JJA5.1± ± ±3.0 SON0.4±0.41.3± ±0.8 TOTAL (Tg yr -1 ) 16.6± ± ±31.9

 Good correlation with Barbados deposition measurements (R=0.74)  Similar monthly variability between model and observations  Observations suggest more dust export during Fall season Tg

Dust Lifetime (days) Season GEOS- Chem MODISRatio DJF MAM JJA SON  Modeled lifetimes are typically 30-50% shorter than from MODIS  Consistently 50% shorter in Spring  Switching off convective removal increases deposition to Amazon by ~50%

AOD  Doubling emissions from Bodélé Depression improves agreement with MODIS and MISR  R increased by ~10% and RMS error decreased by ~35%  Dust deposited to Amazon increased by ~10%

 GEOS-Chem predicts 17±5Tg/yr is deposited in the Amazon, less than half of the 50Tg/yr estimate from satellite  This contrasts with good model agreement with dust deposition measurements in Barbados (R=0.74) and westward dust export comparison with MODIS (250±50 and 240±80Tg/yr respectively)  Modeled dust loss due to wet deposition appears too rapid  A doubling of the dust from the Bodélé depression improves the agreement between the model and satellite observations  Even at the extreme the model and the satellite estimates of dust deposition to the Amazon cannot be reconciled

New GEOSchem Old GEOSchem AERONET Range of obs