UMD AOSC Seminar
Droughts over the US Great Plains and the African Sahel: A Key Role for Atlantic Basin Temperatures
Professor Sumant Nigam
University of Maryland
Department of Atmospheric and Oceanic Science
Earth System Science Interdisciplinary Center
The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and the Atlantic but the relative contribution of the basins in generation of prominent 20thcentury droughts (and wet episodes) is yet to be evaluated, in part, because the SST-forced dynamical models of the atmosphere – a common investigative tool – remain challenged in simulation of regional hydroclimate variability. Here we adopt a statistical approach rooted in a new spatiotemporal analysis of 20th century SST variations and related drought links, which leads to remarkable reconstruction of the major dry and wet episodes over North America; attesting to the extent of the SST influence and facilitating evaluation of the basin contributions.
We find the Atlantic SSTs, tropical and extratropical, to be particularly influential; more than previously indicated, and often, more than the Pacific ones. Statistical drought reconstruction is provided a dynamical foundation from the extraction of SST-circulation links from a nearly century-long circulation record based, in part, on the recent upper-air meteorological analysis of the 1908-1948 period. The links show modulation of moisture transports to be important for drought generation, particularly in the fall. Rudimentary decadal projections based on phase-persistence of multidecadal SST variability suggest wetness over the central-northern Plains in spring-summer and drought conditions in fall.
A preliminary analysis of the drying of the Sahel during 1950s-1980s indicates a substantial contribution from natural SST variability (primarily from the Atlantic) rather than anthropogenic effects.
April 15, 2010, Thursday