| Summary: | As one of the strongest western boundary currents and the surface limb of the Atlantic meridional overturning circulation (AMOC), the stability and variation of the Gulf Stream is a crucial factor to US and European climate. This study examines the variation of the GS and its North Wall, a strong temperature front due to the shoaling of the permanent thermocline, in the following four aspects. First, the representation of the Gulf Stream in 13 state-of-the-art reanalysis products is compared to observations. Common biases are found in all the reanalyses, with the downstream velocity of the Gulf Stream’s underestimated by more than 40%. A theoretical model suggests it is likely due to excessive dissipation from their subgrid-scale parameterizations. Second, the similarities and differences in the behaviors of the Gulf Stream and the North Wall— often considered synonymous in the literature—are analyzed in detail. However, they separate rapidly ~4° downstream of Cape Hatteras due to the presence of mesoscale eddies. Third, the interannual variability of the Gulf Stream and North Wall paths are carefully investigated. The Atlantic Meridional Mode in the tropical Atlantic is found to affect the North Wall position independent from the North Atlantic Oscillation. Fourth, the long-term trends of Gulf Stream properties (transport, latitude, etc.) are examined using along-track altimetry in a stream-following coordinate. This analysis shows that there has been no statistically significant change in Gulf Stream transport or mean latitude since 1993; in other words, the mean state of the Gulf Stream has been stable throughout the altimetry era. The changes in sea surface topography near the Gulf Stream seen in gridded products are largely a result of increasing meridional variability of the Gulf Stream position. Further investigation indicates that the Gulf Stream is not an important contributor to the coastal sea level variability in the Mid-Atlantic Bight and further north. The correlation between the AMOC transport at 26°N and sea level along the US east coast is not related to the Gulf Stream but likely a coincident response to atmospheric forcing.
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