BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Underlying dynamics of glacial millennial-scale climate transition
 s derived from ice-core data - Frank Kwasniok (University of Exeter)
DTSTART:20081016T093000Z
DTEND:20081016T103000Z
UID:TALK13112@talks.cam.ac.uk
CONTACT:Christian Franzke
DESCRIPTION:Simple conceptual nonlinear dynamical models are derived from 
 ice-core data\, thus integrating models and theories with palaeoclimatic r
 ecords. The method is based on parameter estimation using the unscented Ka
 lman filter\, a nonlinear extension of the Kalman filter. Unlike the conve
 ntional linear Kalman filter and the widely used extended Kalman filter\, 
 the unscented Kalman filter keeps the full system dynamics rather than lin
 earising it\, leading to a superior treatment of nonlinearities. The unsce
 nted Kalman filter truncates the filter probability density to a Gaussian 
 in each iteration by only propagating first and second moments but neglect
 ing higher-order moments. The method is applicable to both deterministic a
 nd stochastic models. It offers a practical and computationally cheap alte
 rnative to more complete but also considerably more cumbersome approaches 
 like particle filters or Markov chain Monte Carlo methods.\n\nTwo differen
 t conceptual models for glacial millennial-scale climate transitions (the 
 so-called Dansgaard-Oeschger events) are considered and their parameters e
 stimated from a North Greenland ice-core record. Firstly\, we adopt the mo
 del of stochastically driven motion in a potential that allows for two dis
 tinctly different states. The shape of the potential and the noise strengt
 h are determined from the data. The data reveal that during glacial times 
 the potential is asymmetric and degenerate. There is one stable cold stadi
 al state and one indifferently stable warm interstadial state. Secondly\, 
 a damped stochastically forced nonlinear oscillator is considered. The res
 toring force is given by a bistable potential. The temporal asymmetry of t
 he Dansgaard-Oeschger events is modelled by an asymmetric damping mechanis
 m. The shape of the potential\, the damping coefficient and the noise leve
 l are estimated from the data.
LOCATION:British Antarctic Survey\, Room 330B
END:VEVENT
END:VCALENDAR