Sequential Estimation of Regime Transitions

Wednesday, May 1, 2002 - 10:30am - 11:15am
Keller 3-180
Dmitri Kondrashov (University of California, Los Angeles)
Joint work with M.Ghil, K. Ide, and R. Todling.

Extended-range weather prediction depends in a crucial way on skill at forecasting the onset, duration and break of a blocking event or other persistent anomaly. Such persistent anomalies are known also as weather or flow regimes. The existence of multiple atmospheric flow regimes and the estimation of transitions between them are demonstrated using Marshall and Molteni's (1993) three-level quasi-geostrophic model in spherical geometry. This model of intermediate complexity is shown to have a fairly realistic climatology for Northern Hemisphere winter, and exhibit multiple regimes that resemble those found in atmospheric observations. The Markov chain representation of regime transitions (Ghil, 1987; Ghil and Robertson, 2002) is refined here, for the first time, by finding the preferred transition paths in a two-dimensional subspace of the model's phase space. NASA Goddard's Physical-space Statistical Assimilation System (PSAS) framework is used to carry out identical-twin experiments in which we assess the effects of synthetic observations on pinpointing the transitions between regimes.