Atlantic ITCZ: A Leaky Barrier for African Aerosol

Aaron Adams and Chidong ZhangRosenstiel School of Marine and Atmospheric Science

University of Miami, Miami FL

Total Aerosol Occurrence Frequency at 20˚E in Boreal Summer

DataAerosol: 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

-150 -100 -50 0 50 100 150

-80

-60

-40

-20

0

20

40

60

80

Longitude

Latitude

Summer Total

Summer Dust

Smoke

Dust

Smoke

Polluted Dust

3D Aerosol Seasonal CycleAveraged 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.

Polluted Dust

Dust: blue contourSmoke: green contourPolluted 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

Land Ocean

Land/Ocean

Dust: blue contourSmoke: green contourPolluted Dust: shade

Contour interval: 10%Dashed contour: 30%

Land/Ocean

ERA40 Monthly Means of VW Vectors and RH over West Africa

Gu and Zhang (2002)

Meridional Transport of African aerosol in the Absence of Deep

Convection

Ocean

Land

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.

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.