william k. m. lau nasa/gsfc laboratory for atmospheres co-author: k. m. kim/gest
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Effects of Saharan dusts on weather and climate over the Atlantic:
How Nature foiled the 2006 hurricane forecasts
William K. M. Lau
NASA/GSFC
Laboratory for Atmospheres
Co-author: K. M. Kim/GEST
MODIS Images
Effects of Saharan dusts on weather and climate over the Atlantic
• Annual emission of Saharan dust is estimated to be 4 billion tons
• Increased Saharan dust outbreak since the 1970’s, associated with the prolonged drought in Sahel and increased dust storm over the Sahara desert
Possible weather and climate impacts:
• SAL dry air may suppress tropical cyclogenesis, and/or hurricane formation
• Microphysics effects: suppress warm rain; increase ice-nucleation and deep convection
• Solar Dimming Effect Solar Dimming Effect • “ “ Elevated Heat Pump” EffectElevated Heat Pump” Effect
2005 15H, 12TS, 2TD, 1STS, 1STD
2006 5H, 4TS
How did nature foil the2006 hurricane forecasts?
Dust appears to be the primary cause for SST cooling in the MDR; El Nino is associated with reduced SST (and increased vertical shear) in the eastern equatorial Atlantic, suppresses cyclogensis
El Nino-SSTeffect
Dust-SST“Solar Dimming”effect
More dust means lesser number of days of tropical cyclones
Correlations of HC/TS statistics with a) Barbados dust and b) El Nino SST, 1980-2007
•
TS = sustained wind speed > 34 knts (17 m/s)HC = sustained wind speed >64 knts (33 m/s)
The “Elevated Heat Pump” effect : fvGCM simulation of radiativeEffect on circulation and climate of the West African region
Caribbean Africa
Gulf of Guinea Africa
Estimate of anomalous (aerosol+ water cycle feedback) surface energy flux over the N.
Atlantic/Caribbean region
Short wave flux = -30.4 Wm-2
Longwave flux = 5.9 Wm-2
Sensible heat flux = 2.1 Wm-2
Latent heat flux = 8.6 Wm-2
Net surface flux = -14.1 Wm-2
reducedSW
Anomalous Overturning Circulation induced by“Elevated Heat Pump” effect for WAM
cools ocean
increasedmoisture influx
induced subsidence suppresses convection
reduced SWcools land
dustsource
increased low level clouds
reduced upper level cloudsincreased upper level clouds
Africa
Caribbean Region
West Africa
East Atlantic
Caribbean
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