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CATEGORIES:British Antarctic Survey
SUMMARY:Underlying dynamics of glacial millennial-scale cl
imate transitions derived from ice-core data - Fra
nk Kwasniok (University of Exeter)
DTSTART;TZID=Europe/London:20081016T103000
DTEND;TZID=Europe/London:20081016T113000
UID:TALK13112AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/13112
DESCRIPTION:Simple conceptual nonlinear dynamical models are d
erived from ice-core data\, thus integrating model
s and theories with palaeoclimatic records. The me
thod is based on parameter estimation using the un
scented Kalman filter\, a nonlinear extension of t
he Kalman filter. Unlike the conventional linear K
alman filter and the widely used extended Kalman f
ilter\, the unscented Kalman filter keeps the full
system dynamics rather than linearising it\, lead
ing to a superior treatment of nonlinearities. The
unscented Kalman filter truncates the filter prob
ability density to a Gaussian in each iteration by
only propagating first and second moments but neg
lecting higher-order moments. The method is applic
able to both deterministic and stochastic models.
It offers a practical and computationally cheap al
ternative to more complete but also considerably m
ore cumbersome approaches like particle filters or
Markov chain Monte Carlo methods.\n\nTwo differen
t conceptual models for glacial millennial-scale c
limate transitions (the so-called Dansgaard-Oeschg
er events) are considered and their parameters est
imated from a North Greenland ice-core record. Fir
stly\, we adopt the model of stochastically driven
motion in a potential that allows for two distinc
tly different states. The shape of the potential a
nd the noise strength are determined from the data
. The data reveal that during glacial times the po
tential is asymmetric and degenerate. There is one
stable cold stadial state and one indifferently s
table warm interstadial state. Secondly\, a damped
stochastically forced nonlinear oscillator is con
sidered. The restoring force is given by a bistabl
e potential. The temporal asymmetry of the Dansgaa
rd-Oeschger events is modelled by an asymmetric da
mping mechanism. The shape of the potential\, the
damping coefficient and the noise level are estima
ted from the data.
LOCATION:British Antarctic Survey\, Room 330B
CONTACT:Christian Franzke
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