Dynamic Topography (ERS-1/2 and Seatruth) of Subtropical Ring (Storm 0) in the Storm Corridor (32–34°N, Eastern Basin, North Atlantic Ocean)

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Abstract
Hydrographic measurements were made on RRS ‘Charles Darwin’ Cruise CD97 of the structure of a Subtropical Ring called STORM discovered south-west of the Azores in October 1995 which moved westward along a latitude near 32·5°N. The results showed an elliptical ring structure with a ratio of minor to major axis of 0·6. The external Ring structure extended across a scale of ~400 km in an east-west direction along the major axis of the structure. The internal structure showed isotherms (isopycnals) that were domed upwards by ~200 m. The swirl transport in the Ring was 44 Sv with a negligible barotropic component and the cyclonic flow extended throughout the water column from the surface (maximum ~50cms-1, at a radial distance of ~100km) with reduced intensity to the sea-floor ~4km depth where the flow was effectively zero. The surface currents and dynamic height data showed that the STORM centre was associated with a ~38cm lowering of sea level. The ERS-1 and ERS-2 altimeter surface signature of STORM revealed a similar structure (~42cm sea level depression) but with a larger scale of influence ~500 km. The remote sensing surface elevation structure derived from altimetry also maps (~-600X) changes in the deeper ocean temperature structure and transport (1 cm change equivalent ~ 1 Sv) in the general region. A ~500 d record from a current meter mooring deployed in the region showed three STORM signatures, each separated by a mean of ~180 days. In June 1996, HMS ‘Hecla’ crossed the North Atlantic at a latitude near 33°N and found three STORM temperature signatures.

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