Wind‐Driven Along‐Coast Pressure Gradients in the Middle Atlantic Bight.

Along‐shelf wind stresses drive substantial along‐coast variations in sea level that result in significant along‐coast pressure gradients in the Middle Atlantic Bight (MAB) at time scales from days to years. Forty years of sea‐level data and reanalysis wind stresses are examined to determine the characteristics and dynamics of pressure gradients along the New England and Central MAB coasts. Along‐coast dynamic sea level (pressure) gradients often exceed 5 cm/100 km at daily time scales, 2 cm/100 km at monthly time scales and 0.2 cm/100 km at yearly time scales. Along‐shelf wind stresses account for more than 50% of the along‐coast pressure gradient variance at daily and monthly time scales and more than 25% at yearly time scales. Pressure gradients along the New England coast are primarily driven by local wind stresses along the New England shelf, while pressure gradients along the Central MAB shelf are driven by both local wind stresses along the Central MAB shelf and remote wind stresses along the New England shelf. A steady depth‐average model (Csanady, 1978, https://doi.org/10.1175/1520‐0485(1978)008<0047:tatw>2.0.co;2) accurately reproduces the wind‐driven along‐coast pressure gradients in both regions. The along‐coast pressure gradients typically oppose the local wind stress and, in the along‐shelf momentum balance, are 50%–80% of the along‐shelf wind stress over the inner shelf (water depth 15 m). Plain Language Summary: Along‐coast variations in the wind‐driven set up or set down of coastal sea level results in along‐coast pressure gradients that are an important part of the dynamics that establish currents over the continental shelf. Coastal sea level from tide gauges along the East Coast of the United States from North Carolina to Massachusetts for the 40 year period from 1982 to 2021 are used to estimate the along‐coast pressure gradients and investigate their characteristics. The established along‐coast pressure gradients tend to oppose the local wind stress and consequently reduce the strength of the resulting along‐shelf currents. However, along‐coast pressure gradients are also driven by winds to the north and east of the tide gauge because of a tendency for sea level variations to preferentially spread along the coast from the northeast toward the southwest. This component of the along‐coast pressure gradient forces along‐shelf currents caused by remote wind forcing. A simple, wind‐forced, model that includes this remote forcing accurately reproduces the observed coastal pressure gradients. Key Points: Along‐shelf wind stresses setup substantial along‐coast pressure gradients in the Middle Atlantic Bight at time scales from days to yearsThe along‐coast pressure gradients tend to oppose the wind stress and are driven by both local and remote wind stressesA steady, depth‐averaged, barotropic model proposed by Csanady (1978) accurately reproduces the observed along‐coast pressure gradients [ABSTRACT FROM AUTHOR]