Mesoscale variabilities and gulf stream bifurcation in the Newfoundland basin observed by the Geosat altimeter data

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Abstract
Three years of analysed Geosat altimeter data exhibit mesoscale meanders and eddies in the bifurcation region of the Gulf Stream (GS) into the North Atlantic (NAC) and Azores (AZC) currents over the Newfoundland ridge and Basin. The decorrelation scales of the sea‐surface height variabilities are ∼50 d in time, ∼120 km in the along‐track direction and ∼150 km in the cross‐track direction. Although significant westward propagation is observed in Fourier analysis at speeds of 3 to ∼15 cm s‐1 near the current axes, some individual mesoscale features are chaotic: they are sometimes persistent for several repeat cycles (∼100 d) and then suddenly propagate westward or disappear within one cycle. The GS bifurcation is enhanced by cross‐track smoothing, which minimizes mesoscale features resolved by only one track but retains the larger scale features. The surface geostrophic velocity field with the cross‐track smoothing provides the following description of the bifurcation: the GS starts to split near the ridge, including dipole‐eddy structures, and turns into two branches over the Basin while it flows eastward. The northern branch (the NAC) is persistent with a well‐defined axis, whose position oscillates north and south by 300–400 km twice in the 3‐year time series. The southern branch or AZC with a broader core appears intermittently and has a smaller surface transport than the NAC. Eddy‐eddy interactions may play a role in accelerating/decelerating the NAC when it varies slowly.