20.04.2012: FB1-Seminar

Jonathan M. Lilly, NorthWest Research Associates: "Extracting waves and eddies from Lagrangian trajectories: Theory and preliminary results from the global surface drifter dataset"

15.15 - 16.30, Hörsaal (West), Düsternbrooker Weg 20


The characterization of currents due to different physical mechanisms---inertial oscillations, coherent eddies, and large-scale waves---is an important and challenging data analysis problem. In this talk I present theory, test applications, and show preliminary results from an analysis of the entire Global Drifter Program data set. Two different methods are pursued. The first permits oscillatory motions, such as those associated with coherent eddies, to be automatically extracted from Lagrangian trajectories. This involves connecting ideas from time series analysis, in which one may decompose variability across time using concepts such as 'instantaneous amplitude' and 'instantaneous frequency', to the physical properties of vortices. This allows questions such as the impact of vortex propagation on large-scale heat and vorticity transport to be systematically investigated from observations in a surprisingly direct manner. The second is the use of a stochastic differential equation framework to analyze inertial oscillations. The method is tested against numerical simulations of wind-forced eddy fields, with encouraging results. Examples of strong inertial shifts by coherent eddies are found in the drifter data.