Analysis of the Gulf Stream path and Rossby waves in the North Atlantic based on satellite data.

摘要

This thesis is a part of a larger study of the impact of Rossby waves on the variability of the Gulf Stream path. In the framework of the larger study, this thesis focuses on characterizations of the observed Rossby wave field in the North Atlantic, and of the large scale variability of the Gulf Stream path between Cape Hatteras and the Newfoundland Ridge.;The Rossby wave study, the first manuscript of the thesis, is based on satellite observations of sea surface height. As in previous studies, the wave speed was found to be larger than that expected from theory and the amplitude of the waves to be larger in the western part of the North Atlantic relative to those in the eastern part. Not observed in previous studies is our observation that the more energetic waves in the western part of the basin originate not from the eastern boundary but from a relatively compact source located southeast of the Grand Banks.;The second manuscript in the thesis introduces a method of analysis for two-dimensional (2D) data which, compared with most conventional methods, does not rely on the assumption that the analyzed dynamics are linear and stationary. This method was developed because preliminary analysis of the Gulf Stream path data, analyzed as a latitude value on a longitude-time grid, i.e., a 2D field, revealed significant nonstationarity in both time and space. The proposed method relies on the 1D Empirical Mode Decomposition (EMD) designed specifically for analysis of nonlinear, nonstationary data.;Analysis of the large scale variability of the Gulf Stream path for 1985-2001 using the methodology discussed in the second manuscript is the subject of the third manuscript. This analysis suggests that the observed variability is well represented by a combination of two regimes: (1) quasidecadal unidirectional shifts of the path between Cape Hatteras and the Newfoundland Ridge; (2) bi-modal interannual variations comprised of either a relatively smooth path or a stationary-wave---like structure between Cape Hatteras and the New England Seamount Chain (NESC). We propose a separate index for each regime in order to adequately represent climate scale fluctuations of the path. Our results also suggest that the NESC strongly constrains the Gulf Stream path on larger than annual time scales.