Sea-surface signatures around Madeira

Author: Caldeira, R. M. A., Groom, S., Miller, P., Pilgrim, D., Nezlin, N. P.
2001 pdf 1.82Mb

This is an introductory work that describes the manifestation of the island mass effect phenomena in the atmosphere and at the sea surface for a region of the ocean depleted from oceanographic work - the Madeira Archipelago (33 N, 17 W).

The use of remote sensing tools becomes essential in recognizing some of the sea-surface features that characterize the island mass effect phenomena. AVHRR, coastal zone color scanner (CZCS), and SeaWiFS ancillary National Center for Environmental Prediction (NCEP) data, together with highly developed processing tools from PANORAMA (Processing and Automatic Navigation Of ReAl-time iMAges) allowed the detection of atmospheric Von Karman Vortex Streets, warm water surface wakes, leeward eddies, Azorean front, and localized upwelling.

Results from the remote sensing analysis also helped to promote the reanalysis of historical in situ data for the manifestation of these island effects. IPIMAR cruises carried out between 1979 and 1982 collected temperature, salinity, density, and chlorophyll data, which were reinterpolated at the sea surface to study the island mass effect phenomena for the first time.

Results have shown the formation of a warm water wake south of Madeira Island expanding 400 km offshore. The surface signature of the Azorean front, the so-called subtropical front, seems to take place within the Madeira latitude (33 N). North waters were consistently colder than the warm and salty southern waters. AVHRR data also revealed eddies and fronts being formed in the region. Leeward eddies were often observed in the flanks of the islands; CZCS data showed highly productive eddies in the west of Madeira Island. Localized cold water with high chlorophyll concentrations was also observed around the island’s coast. A particularly dynamic area was the underwater ridge that connected Madeira and Desertas Islands.

Future work should continue to sample these regions of interest with the simultaneous use of different satellite sensors. Vertical characterization of the different phenomena is needed.