2002 Annual

Tuesday, 15 January 2002: 3:00 PM
The influence of Sahel rainfall on the summer circulation of the North Atlantic
James W. Hurrell, NCAR, Boulder, CO
Relatively little attention has been paid to how the climate has varied throughout the annual cycle. In particular, there is a tendency to focus attention on the winter months, which are dynamically the most active. In this paper changes in Atlantic climate are documented throughout the annual cycle, with an emphasis on summer. Summer-time variability is especially important from the perspective of droughts and heat waves, which have large societal impacts. In recent decades, there has been a significant change in the climate of the North Atlantic and Europe during high summer (July-September). Higher-than-average surface pressure, related to an increased tendency for blocking, has led to significantly drier conditions and more frequent episodes of drought. These changes are statistically related to anomalies in tropical Atlantic rainfall, including rainfall over the Sahel. A diagnosis of the physical and dynamical processes involved in these interdecadal climate signals will be presented using ensembles of atmospheric and coupled model simulations.

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