The PEP III Transect within a global climate dynamics context
by
David S. Battisti
University of Washington, Department of Atmospheric Science, Seattle WA 98195-1640

I will summarize the dominant large scale patterns of interannual-to-decadal variability in the present-day climate along the PEP III transect, and present the processes responsible (or hypothesized) for the observed variability. Over Europe and N. Africa, the focus will be on the North Atlantic Oscillation/Arctic Oscillation (NAO/AO); hypotheses for the observed decadal variability (and trend) in the NAO/AO will be briefly discussed. For equatorial and south Africa, I will summarize the empirical and modeling studies link some of the variability in rainfall to ENSO and to atmosphere/ocean interactions in the tropical Atlantic, and discuss the mechanisms involved in these teleconnections.

On millennial time scales, the paleodata suggests marked variability in the climate of Europe and Northern Africa that appears to concomitant with changes in the strength of the thermohaline circulation in the N. Atlantic. Indeed, it has been suggested that the Little Ice Age and the Medieval warm period were the most recent manifestations of the extremes of this millennial-scale thermohaline-climate oscillation, and this "mode" of climate variability extends throughout the majority of Northern Hemisphere and, perhaps, the globe. [The thermohaline-climate oscillation is even more pronounce during glacial epochs, where the global extent of the climate excursions is unambiguous and the climate changes are large in amplitude and often abrupt in time.]

The present hypothesis for the millennial-scale thermohaline-climate "mode" invokes a switch in the the overturning circulation in the (N. Atlantic) ocean, say from ön" to nearly-off, which then causes an abrupt, large cooling over the whole northern hemisphere; the millennial time scales come from the adjustment time of the global ocean.

In this talk I will present observations and calculations that suggests the overturning circulation in the N. Atlantic today has only a modest effect on the wintertime climate of Europe, and an even smaller effect elsewhere. Our results, when applied to the millennial scale "mode" of climate variability, presents significant challenges to the hypothesis that the ocean thermohaline circulation is the driver for this mode of climate variability.

Date received: June 25, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahr-40.