Abstract
The Lagrangian nature of cycling floats is evaluated in the framework defined by the Deep Western Boundary Current of the Mid-Atlantic Ridge. In a statistical approach, speeds and drifts are estimated for an APEX cycling float and compared with the velocities inferred from a park ensemble of four eddy-resolving RAFOS floats. They were deployed at the same location and ballasted for drifting at the same mission depth. Displacement errors induced by geostrophic shear and wind forced currents are analyzed. We observe that the velocity estimated from the RAFOS floats is not statistically different from the velocity estimated from the APEX float. Likewise, the initial separation between the cycling float and a simultaneously deployed RAFOS float has been studied in terms of the turbulent diffusivity. Though the performance of this study in comparable cases without a mean current field may be limited, these oceanic observations support exploiting the Lagrangian nature of the cycling floats.
Highlights
The aim of this paper is to examine to what extent cycling float trajectories can be interpreted in a Lagrangian sense as an instrument which follows the water parcels perfectly, since the displacements during the surfacing intervals prevent them from being truly Lagrangian subsurface floats
The remaining fraction that is advected through Charlie Gibbs Fracture Zone (CGFZ) diverges once again: a northern branch fills the Iceland Basin with Labrador Sea Water (LSW) and the adjacent southern branch joins Iceland-Scotland Overflow Water (ISOW) to originate the deep western boundary current (DWBC) along the eastern side of the Mid-Atlantic Ridge (MAR)
Our numbers during the first three cycles (121.0, 461.4 and 27.9 m2 s–1) are close to those given by Ledwell et al (1998), while the diffusivity coefficient after 60 days falls beyond Ledwell’s κ estimates. In view of this result, during the first three cycles we can relate the deviation observed between the floats to the turbulent diffusivity, though our numbers cannot be considered as estimates of the actual diffusivity coefficient. According to their large scale trajectories, both types of floats prove the presence of a Deep Western
Summary
Intercomparing drifts from RAFOS and profiling floats in the deep western boundary current along the Mid-Atlantic Ridge*. Speeds and drifts are estimated for an APEX cycling float and compared with the velocities inferred from a park ensemble of four eddy-resolving RAFOS floats. They were deployed at the same location and ballasted for drifting at the same mission depth. RESUMEN: COMPARACIÓN DE FLOTADORES RAFOS Y DERIVADORES-PERFILADORES AUTÓNOMOS APEX EN LA CORRIENTE PROFUNDA DE FRONTERA OESTE DE LA DORSAL CENTROATLÁNTICA. – En este trabajo se examina la naturaleza lagrangiana de los derivadores-perfiladores autónomos en el contexto definido por la Corriente Profunda de Frontera Oeste de la Dorsal Centroatlántica. Palabras clave: derivador-perfilador autónomo, APEX, RAFOS, Lagrangiana, Corrriente Profunda de Frontera Oeste
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