Spatial and Temporal Variability of the Gulf Stream Near Cape Hatteras

Abstract

AbstractIn situ observations from a 19‐month deployment of current‐ and pressure‐sensor equipped inverted echo sounders (CPIESs) along and across the Gulf Stream near Cape Hatteras capture spatial and temporal variability where this western boundary current separates from the continental margin. Regional hydrographic casts and two temperature cross‐sections spanning the Gulf Stream southeast of Cape Hatteras are used with the CPIESs' records of acoustic travel time to infer changes in thermocline depthDTand Gulf Stream position. Wave‐like Gulf Stream meanders are observed where the Stream approaches the separation location with periods less than 15 days, wavelengths less than 500‐km, and phase speeds between 40 and 70 km d−1. Though meander amplitudes typically decrease by ∼30% on the final approach to Cape Hatteras, some signals are still coherent across the Gulf Stream separation location. Temporal variability in meander intensity may be related to the Loop Current ∼1,400 km upstream. Mesoscale variability is strongest downstream of the separation location where Gulf Stream position is no longer constrained by the steep continental slope. Low frequency transport changes in the Florida Straits are correlated with sea‐surface height gradients along the entire South Atlantic Bight (SAB) and withDTinferred at the CPIES sites. The correlations withDTare likely due to coherent transport anomalies in the Gulf Stream approaching the separation location, which then drive Gulf Stream position changes downstream of the separation location. The patterns of coherent transport anomalies may reflect large‐scale atmospheric forcing patterns or rapid equatorward propagation of barotropic signals along the SAB.