Observation of a Fast Continental Shelf Wave Generated by a Storm Impacting Newfoundland Using Wavelet and Cross-Wavelet Analyses

Wavelet and cross-wavelet power spectra of sea level records from tide gauges along the Atlantic coast of Canada showed a low- frequency barotropic response after Hurricane Florence crossed the Newfoundland shelf in September 2006. In comparison with two other storms, the results showed that Florence was the only one that excited a propagating sea level disturbance with a period range similar to the passage time of the storm over the shelf (26-30 h) and phase shifts consistent with a barotropic continental shelf wave (CSW). The high amplitude of the oscillations generated by Florence along the shore diminished from approximately 45 to 12 cm as the CSW propagated from the south coast of Newfoundland to the southern Nova Scotia seaboard. This paper presents the first direct measurement of a remarkably high alongshore group speed (11.4 +/- 5.9 m s (1)), in the manner of free-barotropic CSW, by examination of sea level wavelet power spectra at different locations. Furthermore, using cross-wavelet analysis of pairs of stations, an exceptional phase speed of 16.0 +/- 5.1 m s (-1) has been found, greater than had been previously observed for a free CSW. The results were consistent with dispersion curves for the first-mode barotropic CSW.