Temporal variation of meandering intensity and domain‐wide lateral oscillations of the Gulf Stream

Abstract

The path of the Gulf Stream exhibits two modes of variability: wavelike spatial meanders associated with instability processes and large‐scale lateral shifts of the path presumably due to atmospheric forcing. The objectives of this study are to examine the temporal variation of the intensity of spatial meandering in the stream, to characterize large‐scale lateral oscillations in the stream's path, and to study the correlation between these two dynamically distinct modes of variability. The data used for this analysis are path displacements of the Gulf Stream between 75° and 60°W obtained from AVHRR‐derived (Advanced Very High Resolution Radiometer) infrared images for the period April 1982 through December 1989. Meandering intensity, measured by the spatial root‐mean‐square displacement of the stream path, displays a 9‐month dominant periodicity which is persistent through the study period. The 9‐month fluctuation in meandering intensity may be related to the interaction of Rossby waves with the stream. Interannual variation of meandering intensity is also found to be significant, with meandering being much more intense during 1985 than it was in 1987. Annual variation, however, is weak and not well‐defined. The spatially averaged position of the stream, which reflects nonmeandering large‐scale lateral oscillations of the stream path, is dominated by an annual cycle. On average, the mean position is farthest north in November and farthest south in April. The first empirical orthogonal function mode of the space‐time path displacements represents lateral oscillations that are in‐phase over the entire study domain. Interannual oscillations are also observed and are found to be weaker than the annual oscillation. The eigenvalue of the first mode indicates that about 21.5% of the total space‐time variability of the stream path can be attributed to domain‐wide lateral oscillations. The correlation between meandering intensity and domain‐wide lateral oscillations is very weak.