Lee region of Gran Canaria

Abstract

The mountainous Canary Islands present obstacles to the trade winds and to the Canary Current flowing equatorward past them. In situ observations of hydrographic properties and surface winds south of Gran Canaria, together with advanced very high resolution radiometer and synthetic aperture radar images during 2 weeks in summer 1995 are analyzed. A cyclonic eddy shed from the west of the island drifted southwestward at 5 cm s−1, while the southeast coast was approached by an upwelling filament originating off NW Africa. A wind lee region bounded by intense horizontal shear lines had a weak return islandward wind in its center. The lee formed a triangular, diurnally varying, warm water pool with two sea surface temperature maxima separated by lower temperatures below the return wind. Shallow temperature stratification occurred behind the island in contrast to the uniform surface mixed layer in exposed regions. Upwelling and downwelling of 10–20 m d−1 were indicated on the cyclonic and anticyclonic sides of the lee region. In the SAR images, lines of strong current shear along a temperature front between the cyclonic eddy and the upwelling filament were identifiable. However, the radar images were dominated by atmospheric phenomena, including mountain lee wave packets, windrows, and wind shear lines. Estimation of the wind field from the SAR backscatter intensity revealed complex structure and intensification on the edges of the warm lee.