Water Masses and Mesoscale Circulation of North Rockall Trough Waters during JASIN 1978 [and Discussion]

D. J. Ellett, P. Kruseman, G. J. Prangsma, R. T. Pollard, H. M. V. Aken, A. Edwards, H. D. Dooley, W. J. Gould, J. A. Businger, J. G. Harvey
1983 Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences  
During the Joint Air-Sea Interaction Experiment (JASIN 1978) grids of temperature and salinity profiles were worked within an area of about 150 km x 150 km to obtain details of the mesoscale circulation around the location of the experiment in the North Rockall Trough. Data were also obtained from moored current meters and from research vessel observations in the surrounding waters. In the uppermost layers two water masses were present, North Atlantic Water from southern parts of the Rockall
more » ... ugh and fresher Modified North Atlantic Water from the north and west. Beneath these an intermediate water formed by Atlantic Water in contact with Subarctic Intermediate Water was found and at greater depth distinc tions could be drawn between water from the south, water with an admixture of Norwegian Sea Deep Water from the Scotland-Iceland ridges and, more sparse, water with a component of Arctic Intermediate Water from the Faroe-Shetland Channel. The patterns of circulation were found to change little between the lower depths and 200 m. An anticyclonic eddy of fresher, colder water moved westwards across the northern half of the grid at about 1.4 km day-1, the northern sector of a more saline meander expanded westwards across the southern part of the area, and smaller less well resolved circulations were found in the west. The eddy contained water of overflow origin and the meander appears to have been part of the main Atlantic to Norwegian Sea current. When inverse analysis was applied to two of the data sets to investigate choices of reference level, zero velocity at the bottom gave the only physically realistic solution. Although the necessary process of averaging the observations to data points 45 km apart obscured the resolution of smaller features, confidence in the reference level that satisfied the inverse analysis allowed classical geostrophic analysis to be performed on the full set of stations, supporting and quantifying the earlier analysis of patterns. The influence of the deeper circulation can be seen in the modification of the thermo haline structure in the seasonal thermocline and mixed layers. Boundaries between adjacent upper water masses were distorted by underlying convergences or fragmented by horizontal shears. I n t r o d u c t io n The main features of ocean circulation within the northeast Atlantic arise from the relatively warm and saline water of the Atlantic Current entering the area from the west and southwest close to 50° N, where the Charlie-Gibbs Fracture Zone disrupts the Mid-Atlantic Ridge, and from the colder, fresher waters spreading southeastward from the Labrador Sea. The oceanic [ 11 ]
doi:10.1098/rsta.1983.0002 fatcat:lhsjmtmmafeovfvqyks5gjmfxa