Observations on the propagation, growth, and predictability of Gulf Stream meanders

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Abstract
During a 3‐year period, Gulf Stream positions determined by satellite infrared imagery on a grid northeast of Cape Hatteras have been correlated against “inlet” path parameters (displacement from the mean position, angle, and curvature) monitored by an array of inverted echo sounders (IES). By cross‐spectral calculations between these measurements, we determined the downstream coherences, phase speeds, and spatial growth rates. The downstream path predictability from these inlet parameters was tested in a multiple input linear response model. The most energetic meanders, with periods of 33–50 days, remained highly coherent for 300 km downstream, roughly the dominant wavelength, with marginal coherence again at 500–575 km. Phase speeds are frequency dependent and decrease with distance downstream. For the 50‐(33) day meanders, phase speeds decreased from 10 (17) km/d at the inlet to 6 (8) km/d at a distance downstream of about 550 km. The average growth rate (spatial e‐folding wave number) over the entire region is 1.3×10−3 km−1. Within 300 km of the inlet, the multiple coherence accounts for 55–65% of the total path‐displacement variance, with displacement and angle being the best individual predictors in the first and last halves of this region, respectively.