PAOC Colloquium

PAOC Colloquium: Nathan Steiger (LDEO)
Date Time Location
October 30th, 2017 12:00pm-1:00pm Ida Green Lounge
Title: What caused the Medieval megadroughts of western North America?

Abstract: The apparent clustering of decadal-scale megadroughts prior to circa 1600 is one of the most prominent features of the drought record in much of North America. These droughts are seen clearly in the tree ring-based North American Drought Atlas as well as in several independent lines of geological evidence. Despite their prominence, the causes of such megadroughts and their clustering are not well-understood. The difficulty in understanding these megadroughts is due largely to the lack of long-term climate dynamics information that is physically consistent with reconstructions of past hydroclimate. Here I will diagnose the dynamical causes of the Medieval megadroughts of western North America using a data assimilation-based reconstruction; this technique works by optimally combining proxies with climate models to reconstruct both hydroclimate fields and the corresponding atmosphere-ocean states. Using these reconstructions, I will discuss tests of prominent hypotheses about the dynamical causes of megadroughts and their clustering in the Medieval period. I will focus particularly on hypotheses relating to changes in local climate, shifts in the mean state of the tropical Pacific or the Atlantic, and changes in the frequency of occurrence of La Nina-like states in the Pacific.

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