Atmospheric Controls on North African Dust Emission

Richard Washington

Sebastian EngelstaedterMartin Todd, Gil Lizcano

Fiona MitchellYoram Kaufman, Ilan Koren

Oxford, UCL, GSFC NASA,

JANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC

Annual dust cycle of TOMS AI (1980-92)

Washington and Todd 2005 GRL

Mean JFM Zonal Wind: latitude-height along 18 E

Washington and Todd 2005 GRL

Bodele daily dust Vs 1000 hPa geopotentials and 950 vector winds (JFM)

Tibesti

EnnediGap FlowBodele LLJ

Palaeo Lake

Phase of TOMS AI1980-1992

Dust in Colour

Rainfall black contours

Annual Cycle of TOMS AIVs Annual Cycle of ERA-40Surface Wind

Annual Cycle of TOMS AIVs Annual Cycle of ERA-40

Surface Divergence

Mean TOMS AI for main dust season May-Aug (1980-92)

WA1WA2

WA3

WA4

BOD EA

WA1 WA2 WA3 WA4 BOD EA

Mean TOMS AI for dust season May-Aug (1980-92)

Engelstaedter and Washington in prep

Annual Cycle of TOMS AIVs Annual Cycle of ERA-40

surface gustiness

• Eastern Sahara (Chad): Mean wind controls aerosol production

• Western Sahara (Mali/Mauri heat low): surface convergence and wind gustiness fits annual cycle better

Parcel trajectory density climatology

July (1979-98)

Djouf region (17.5-22.5N, 2.5-7.5W)

% trajectories remain over Sahara (> 15N < 30N) 69 33 6

% trajectories crossing the 15W meridian 33 66 83

After days 3 5 10