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