1. Atlantic ITCZ: A Leaky Barrier for African Aerosol Aaron Adams and Chidong Zhang Rosenstiel School of Marine and Atmospheric Science University of Miami, Miami FL

2. Total Aerosol Occurrence Frequency at 20˚E in Boreal Summer

3. Data Aerosol: CALIPSO Level 2 Vertical Feature Mask Validated Stage 1 Version 3 ITCZ rainfall: TRMM 3B42 Daily Gridded Wind: ERA-Interim Reanalysis Period: Boreal summer 2006 – 2010

4. Summer Total

5. Summer Dust Smoke

6. Dust Smoke Polluted Dust 3D Aerosol Seasonal Cycle Averaged 31°W-60°E Dust migrates south of the ITCZ all year Smoke does not cross ITCZ except in boreal winter (Sahel source) Polluted dust is maximum in the ITCZ region.

7. Polluted Dust Dust: blue contour Smoke: green contour Polluted Dust: shade Contour interval: 10% Dashed contour: 30% Dust migrates south of the ITCZ at all levels Smoke is confined south of the ITCZ at all levels Polluted Dust is prevalent due to external mixing Summer

8. LandOcean Land/Ocean Dust: blue contour Smoke: green contour Polluted Dust: shade Contour interval: 10% Dashed contour: 30% Land/Ocean

9. ERA40 Monthly Means of VW Vectors and RH over West Africa Gu and Zhang (2002)

10. Meridional Transport of African aerosol in the Absence of Deep Convection Ocean Land

11. Summary ITCZ acts as a barrier for African aerosol when deep convection and heavy rain are present. Cross-ITCZ transport of aerosol is possible due to shallow meridional circulation (SMC) when deep convection is absent. ITCZ is thus a leaky barrier for African aerosol.

12. Thank You CALIPSO data were obtained from the NASA Langley Research Center Atmospheric Science Data Center. TRMM data were obtained from the Goddard Distributed Active Archive Center (GES DISC DAAC). Wind reanalysis data were obtained from the ECMWF ERA-Interim data holdings.