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TITLE:
"The fluid dynamics of
climatic variations."
SPEAKER:
Professor Walter A. Robinson,
TIME: Thursday Jan. 13, 2005 at 4 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)
University of Illinois at Urbana-Champaign
Humans are susceptible to anomalous weather conditions that persist: a dry
summer damages crops; an unusually cold winter drives up the price of oil;
an abnormally wet spring sends rivers out of their banks. Such
occurrences, which last too long to be attributed to one or even a few
storms, are variations in the climate. Climatic variations do not occur on
preferred timescales -- there are no peaks in their power spectra -- but
they do exhibit preferred spatial scales and structures. We seek to
understand why these structures persist and to determine the extent to
which such persistent climatic variations can be predicted.
Outside of the tropics, climatic variations arise primarily from the
internal fluid dynamics of the atmosphere. Consideration of the simplest
relevant representation of atmospheric dynamics, a two-dimensional fluid
on a rotating spherical Earth, suggests long-lived atmospheric anomalies
should appear as Rossby waves of a particular scale and as axisymmetric
structures. Climatic variations of both types are found in meteorological
data. The persistence of these structures against the dissipative
influences of dispersion and surface drag, however, can be understood only
with more complex models, which include the two-way interactions of
climatic variations with transient weather systems. This weather-climate
coupling also determines how the extra-tropical atmosphere responds to
external perturbations, ranging from El Niño to global warming.