A comparison of observed and modeled sea surface topographic time series near the New England seamounts

Abstract

Yearlong data records from four arrays of inverted echo sounders (IES) equipped with pressure sensors from the northwest Atlantic and 2‐year records from a two‐layer, primitive‐equation numerical model of this region (including a prescribed deep western boundary current) are compared. Standard deviations of barotropic and total sea surface topographic variability and the correlations between them are examined as a function of horizontal position. Variances contained in three spectral bands (secular, longer than 150 days; mesoscale, 20–150 days; and high frequency 2–20 days) are also examined. The eastward penetration scale of modeled Gulf Stream variability shows a significant improvement over a previous comparison (Hallock et al., 1989). Standard deviations of observed sea surface height components compare favorably with those derived from model output, with maxima of about 30 cm (10 cm for the barotropic contribution). High correlations (0.6–0.8) between surface height and the barotropic component are found for both model and observations. Spectral shape is dominated by the temporal mesoscale east of the New England Seamounts for both observed and modeled variability. West of the seamounts, the secular (low frequency) band becomes more important, particularly for the surface height variability; this result is more pronounced for model output. Gulf Stream geostrophic current direction statistics from IES dynamic heights compare favorably with those derived from model dynamic heights upstream and downstream of the seamounts.