[Virtual] GFDL Seminar

Wed, May 20, 2020, 10:00 am to 11:00 am

As one of the strongest western boundary currents and the surface limb of the Atlantic Meridional Overturning Circulation, the Gulf Stream is one of the most important oceanic paths for poleward heat and salt transport. Variations of the Gulf Stream are a crucial factor affecting local and European climate. This presentation will first examine the representation of the Gulf Stream in 13 state-of-the-art reanalysis products by observations. A large spread across reanalysis products is found. Less than half of the reanalysis products show significant correlations (at 95% level) with observations for the Gulf Stream separation latitude at Cape Hatteras and the Gulf Stream transport between New Jersey and Bermuda. All those reanalyses are found to underestimate the Gulf Stream’s maximal velocity by more than 40%, likely due to excessive dissipation from their subgrid-scale parameterizations. Among the evaluated reanalysis products, HYCOM and GLORYS2v4 stand out for their superior performance by most metrics.  Some studies suggested that the Gulf Streamhas weakened in recent years. In the second part of the presentation, the mean state of the Gulf Stream will be evaluated using along-track altimeter data in stream-following coordinates. This analysis shows that there has been no statistically significant change in the Gulf Stream transport, mean latitude,downstream velocity and width since 1993. The changes in sea surface height 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 north of Cape Hatteras.

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