Island-induced eddies in the Canary islands

Abstract Cyclonic and anticyclonic eddies were observed downstream of Gran Canaria (Canary Islands), an almost circular island of about 50 km diameter, located in the path of the Canary Current. Temperature data were obtained from five AXBT and one CTD surveys carried out during two years (April, May and December, 1989; February, May and June, 1990), and from NOAA AVHRR (Advanced Very High Resolution Radiometer) sea surface temperature (SST) satellite images. The presence of eddies in most of the surveys and in many SST images suggests that they are common mesoscale features in the flow past the island througout the year. In general, eddy diameter is similar to the width of the island, while the vertical extent is from the near-surface layers down to at least 400 m depth. However, vertical sections across the eddies show distinct patterns in their structures which could correspond to different stages of development. Wakes of relatively warm surface water develop in the lee of the island, interacting with the eddies and affecting their upper mixed layer structure. It is hypothesized that eddies are sequentially spun off from the island with a period ranging from several days to two weeks. If this is the case, they could contribute to the high levels of eddy kinetic energy observed recently downstream of the Canarian archipelago from moored current meters.

[1]  L. Stramma.  Geostrophic transport in the Warm Water Sphere of the eastern subtropical North Atlantic , 1984 .

[2]  New products and projects , 1988 .

[3]  K. P. Chopra.  Atmospheric and Oceanic Flow Problems Introduced By Islands , 1973 .

[4]  G. Siedler,et al.  Seasonal changes in the North Atlantic subtropical Gyre , 1988 .

[5]  J. Arístegui,et al.  Phytoplankton pigment patterns in the Canary Islands area as determined using Coastal Zone Colour Scanner data , 1993 .

[6]  B. Klein,et al.  On the origin of the Azores Current , 1989 .

[7]  P. L. Borgne,et al.  Operational measurement of sea surface temperatures at CMS Lannion from NOAA-7 AVHRR data , 1986 .

[8]  L. F. Hubert,et al.  Kármán Vortex-Streets in Earth's Atmosphere , 1964, Nature.

[9]  W. Zenk,et al.  The Madeira Mode Water , 1987 .

[10]  James J. Simpson,et al.  A mesoscale eddy dipole in the offshore California Current , 1990 .

[11]  S. Meacham,et al.  Vortices in shear , 1989 .

[12]  L. F. Hubert,et al.  Mesoscale Eddies in Wake of Islands. , 1965 .

[13]  Tee Tai Lim,et al.  The vortex-shedding process behind two-dimensional bluff bodies , 1982, Journal of Fluid Mechanics.

[14]  John D. McCalpin.  On the adjustment of azimuthally perturbed vortices , 1987 .

[15]  E. Mittelstaedt.  The ocean boundary along the northwest African coast: Circulation and oceanographic properties at the sea surface , 1991 .

[16]  P. Davies,et al.  A laboratory study of the lift forces on a moving solid obstacle in a rotating fluid , 1989 .

[17]  P. Schlittenhardt,et al.  Upwelling and boundary circulation off Northwest Africa as depicted by infrared and visible satellite observations , 1991 .

[18]  G. Flierl,et al.  On the interaction of a vortex with a shear flow , 1987 .

[19]  P. Richardson,et al.  A quasi‐synoptic survey of the thermocline circulation and water mass distribution within the Canary Basin , 1986 .

[20]  T. Müller,et al.  Multi-year current time series in the eastern North Atlantic Ocean , 1992 .

[21]  P. Falkowski,et al.  Role of eddy pumping in enhancing primary production in the ocean , 1991, Nature.

[22]  B. Eaton.  Analysis of laminar vortex shedding behind a circular cylinder by computer-aided flow visualization , 1987, Journal of Fluid Mechanics.

[23]  D. Boyer,et al.  Vortex shedding in rotating flows , 1983 .