Gulf Stream frontal statistics from Florida Straits to Cape Hatteras derived from satellite and historical data

Abstract

A 5 year record (1976–1980) of weekly Gulf Stream paths digitized from the U.S. Navy Ocean Frontal Analysis is analyzed to define a mean Gulf Stream path and weekly space‐time series of fluctuations about the mean between the Florida Straits and Cape Hatteras. This satellite‐derived Gulf Stream frontal mean locus is used as a natural coordinate system in which NODC historical expendable bathythermograph (XBT) data is averaged to determine the mean cross stream hermal structure. The results show that the satellite‐derived front; that is, the cold wall of the stream as derived from IR imagery is in good agreement with a classical definition of the stream path. The Gulf Stream path is discussed in relationship to the bottom topography. Frontal location time series at various locations along the Gulf Stream are analyzed to generate occupation statistics and spectra for stream position. A steady increase in the variance of stream position occurs from Cape Canaveral to the Charleston Bump. This trend is followed by a sharp increase in variance just downstream of the bump and then a gradual decay from approximately 33°N to Cape Hatteras. A similar distribution of variance is found in the depth of the 15°C isotherm. An annual signal is seen in the path data all along the U.S. east coast. The stream front north of Charleston (∼32°N) exhibits the strongest annual variation with the surface front being further offshore in the late winter and early spring. This annual signal is not obvious at the thermocline level (15°C). It is consistent, however, with observed shifts in the isotherm patterns in the upper 100 m.