The primary objectives of NORCSEX included studies of SAR imaging of surface current features, SAR imaging of ocean surface gravity waves, combined airborne SAR and ship-mounted scatterometer measurements of near-surface wind fields, radar altimeter measurements of sea surface topography, significant wave height, and wind speed, integrated use of SAR and radar altimeter for significant wave height measurements, and comparison and validation of numerical ocean circulation model results to remote sensing and in situ observations. See Johannessen (1991).
NADW originates in the northern North Atlantic in the GIN Sea. The main sources in are the dense overflows on either side of Iceland from intermediate depths in the Nordic Seas, the lower part of the Labrador Sea Water (LSW) layer including both a recirculating and an entraining component, and a recirculating Antarctic Bottom Water (AABW) derivative of southerly origins in the deepest layers of either basin.
The total direct transport of the dense overflows is about 5.6 Sv, about equally divided east and west of Iceland over the various sections of the Greenland-Scotland Ridge. The sill depth in the Denmark Strait to the east of Iceland is 600 m. To the west is is 450 m on the Iceland-Faroe Ridge and 850 m in the Faroe Bank Channel. The most saline of the overflows in through the Faroe Bank Channel which, although it overflows as a relatively fresh source, mixes intensely with overlying warm saline water from the local thermocline to become more saline. This water has been labeled by some as Northeast Atlantic Deep Water (NEADW). The coldest and densest of the overflows is the Denmark Strait Overflow, which has a characteristic salinity minimum. This overflow has been sometimes labeled as Northwest Atlantic Bottom Water.
The AABW component passes into the eastern GIN Sea basin through the Vema Fracture Zone at 11 N at a rate of about 2.0-2.5 Sv. This eventually combines with the overflows east of Iceland to give an estimated 6.6 Sv of flow west through the Charlie Gibbs Fracture Zone. This flows west to combine with the overflow west of Iceland, which has mixed with the LSW to contribute to a total eventual southward flow of NADW east of Newfoundland of about 13 Sv. The recirculation and entrainment processes that increase the 5.6 Sv of overflow water to the 13 Sv of NADW flowing south are the least well known parts of NADW formation. See Dickson and Brown (1994) for the present best summary of NADW formation processes.
The resulting mixture, as it moves south, is conventionally separated into upper, middle and lower NADW. Upper NADW comes from Mediterranean outflow spreading into the Central and North Atlantic at depths of 1000 to 1500m, while middle NADW is formed by ocean convection in the Labrador Sea flowing into the Western North Atlantic Basin. Lower NADW is formed by a complex series of mixing flows over the Greenland-Scotland Ridge and thereafter, and comprises the bulk of the totality of NADW. The middle and lower forms of NADW are additionally identified by two oxygen maxima in the subtropics at 2000-3000 m and 3500-4000 m, respectively. See Warren (1981).
The NBC originates south of the equator where the South Equatorial Current approaches the coast. Historically, it was thought to be simply the northward flowing part of the bifurcation of the Central South Equatorial Current (CSEC) at near 5 S (with the Brazil Current (BC) the southward flowing part), but recent investigations have shown a more complicated picture. The simple view was prompted by surface current distributions obtained from ship drift and surface drifter trajectories, which turn out to have obscured the overall geostrophic flow patterns.
Geostrophic calculations have shown that the NBC originates just south of 10 30' S where the convergence of the southern branch of the CSEC with part of the Southern South Equatorial Current results in a transport (relative to 1000 m) of about 21 Sv at near 10 S. It continues north from there and eventually merges with the northern branch of the CSEC just north of 5 S where the transport has increased to the aforementioned 37 Sv. See da Silveira (1994).
where is the sampling interval. It is the maximum frequency that can be detected from data sampled at time spacing . Higher frequencies are subject to aliasing which can cause the spectrum to differ from the true spectrum. See Nyquist theorem. See Peixoto and Oort (1992).