2B.2
Dust interaction with african climate (Invited)
Natalie Mahowald, Cornell University, Ithaca, NY; and M. Yoshioka and A. M. Sealy
The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the 20th century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). Our model uses dust that is less absorbing in the shortwave band and larger particle sizes than other simulation studies. As a result, our simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction, but this effect could be due to factors other than desert dust aerosols (e.g., biomass burning aerosols and other low-frequency processes). Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant due to small number of years in the simulation. Simulations including a dynamic vegetation model as well as interactive dust also suggest that dust is more important than vegetation is driving shifts in vegetation. Although the estimated values of impacts are likely to be model dependent, our analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.
Recorded presentationSession 2B, African Climate: II. African Easterly Waves and Dust
Monday, 21 January 2008, 10:45 AM-11:45 AM, 217-218
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