Accession Number : ADA580642


Title :   Surface Circulation in the Iroise Sea (W. Brittany) from High Resolution HF Radar Mapping


Descriptive Note : Journal article


Corporate Author : NAVAL RESEARCH LAB STENNIS DETACHMENT STENNIS SPACE CENTER MS OCEANOGRAPHY DIV


Personal Author(s) : Sentchev, Alexei ; Forget, Phillippe ; Barbin, Yves ; Yaremchuk, Max


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a580642.pdf


Report Date : Jan 2013


Pagination or Media Count : 19


Abstract : The data from two high-frequency radars (HFR) operating in the Iroise Sea are re-processed by applying an improved version of the direction finding algorithm, removing wave-induced surface currents and the variational interpolation on a regular grid. Combining these processing techniques allowed reconstruction of the surface currents at a level of details that was not previously available. Refined resolution enabled to identify fine-scale structures of surface circulation, to quantify the variability of tidal currents and the residual (time averaged) velocity field, and to explain spatial intermittence in polarization of the tidal current ellipses. The analyzed data span two month-long periods in spring and late summer of 2007. The major findings include (a) a dipole structure in the vorticity field characterized by two oppositely rotating eddies, generated on the leeward side of the Ushant Island at flood (negative polarity) and at ebb (positive polarity); (b) an extremely strong fortnightly variability of tidal currents northwest of the Ushant Island with the highest velocity magnitude of 3.9 m/s caused by the interference of the major semi-diurnal tidal constituents; (c) a significant contribution of the higher order nonlinear tidal harmonics to the surface currents in the Fromveur strait, which maintains strong tidal currents and affects the shape of their fortnightly modulation. The residual circulation is characterized by two distinct zones approximately separated by the 100 m isobath: in the offshore zone the residual currents have a significant contribution of the wind-driven component, whereas the nearshore zone is characterized by extremely strong (up to 0.4 m/s) time-independent residual circulation featuring two permanent anticyclonic eddies: north of the western extremity of the Sein archipelago, and north the Ushant Island. The acquired data and the presented results could be useful for regional model validation and studies of the local eddy dynamics,


Descriptors :   *OCEAN CURRENTS , *RADAR MAPPING , *TIDAL CURRENTS , ALGORITHMS , DOPPLER RADAR , EDDY CURRENTS , FRANCE , HIGH FREQUENCY , HIGH RESOLUTION , ISLANDS , VELOCITY , WIND


Subject Categories : Cartography and Aerial Photography
      Physical and Dynamic Oceanography


Distribution Statement : APPROVED FOR PUBLIC RELEASE