The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

Verification of Climate Forecasts (Discussion)
Speaker: Ian Jolliffe
Beyond Ensembles: <strong>The</strong> Application and Improvement of Climate Simulations
Speaker: Leonard Smith
Professor Leonard Smith
London School of Economics, Centre for the Analysis of Time Series (CATS)
lenny@maths.ox.ac.uk
Climate models are large nonlinear dynamical systems which insightfully but
imperfectly reflect the evolving weather patterns of the Earth. In the theory of nonlinear
dynamical systems, the concept of shadowing is employed to describe the ability of one
mathematical system to admit trajectories which remain close to the trajectory of another
mathematical system, as the two evolve in time. This idea is generalised to the case where we
have one mathematical dynamical system and observations of a physical system. Recent
applications to operational weather models are used to justify the likely applicability of this
approach in the climate context. Ensemble experiments sample the various uncertainties and
inadequacies of the available models, and yield useful information on model behaviour. <strong>The</strong>
high dimension of the model-state spaces and our ignorance of how to to sample the space of
model structures limit our ability to improve and interpret our models using the ensemble
approach.
<strong>The</strong>se limits are highlighted, from the decision makers perspective, with figures from the
<strong>2007</strong> IPCC Summary for Policy Makers. Our ability to address the needs of decision makers
via ensemble experiments is discussed, and contrasted with the information which could be
extracted from shadowing experiments. In the climate context, shadowing experiments identify
pseudo-orbits of the model over relatively well-observed historical periods (say, 1950-2006).
Poster Session
Detected shift of Mediterranean cyclone tracks using the ERA-40 database
Judit Bartholy
Dept. of Meteorology, Eotvos Lorand University, Budapest, Hungary
105