Thursday, 18 January 2007: 4:45 PM
A diagnostic study of atmospheric blocking using Lyapunov exponents over a 50 year period
214B (Henry B. Gonzalez Convention Center)
Lyapunov exponents can quantify the average predictability and stability properties of a dynamical system without the need to explicitly solve for the flow streamfunction. Thus, Lyapunov exponents (i.e., the eigenvalues of the linearlized decomposition of the steady state flow) may be used as a diagnostic tool especially in blocking studies. Lyapunov exponents are estimated for several blocking episodes occurring in the Southern Hemisphere (SH) using the NCEP gridded re-analysis data over a 50-year period. The role of the large-scale flow in formation, maintenance as well as in decay of the several selected SH blocking events is discussed in terms of Lyapunov exponent time variability. It is noted that an abrupt change (decrease/increase) in the hemispheric and/or regional Lyapunov exponent values occur indicating an unstable large-scale flow during the blocking onset/decay period. Correlation of Lyapunov exponents with a theoretically appealing quantity namely the enstrophy is also investigated in light of the analyzed data for several case studies. A comparison of our findings with the Lyapunov exponent behavior for NH blocking events is also presented.