NEAT GIN – North East Atlantic, Greenland-Iceland-Norwegian sea experiment

The NEAT GIN experiment took place during September-October 1989 at the Norwegian shelf edge near 68°N. Seven moorings, five in a closely-spaced cross-slope section, have proved a valuable precursor to the Shelf Edge Study (SES) west of Scotland. The NEAT GIN data analysis has now been completed.
A mean current (0.2-0.3 m/s) north-eastwards along the slope was found to be a predominant feature and is common to many locations around the north-west European shelf edge. The total transport was estimated to be 4 to 9 106m3/s, values at the upper end of the range of estimates from elsewhere around north-west Europe. Measurements near to the bottom showed slight anti-clockwise veering, consistent with the presence of a bottom Ekman layer.
Rotary motion, coherent down to about 300 m, made another large contribution to the total flow. Most energy occurred in periods exceeding 2 days (« day at the top of the slope). Comparisons with hindcast meteorological data showed little evidence of correlation between this rotary flow and the weather. Hence a stochastic source mechanism is suggested, eg. baroclinic instability.
Tidal analysis of the currents showed modest values; the M2 component was largest, about 0.05 m/s at the top of the slope in 200 m water depth, decreasing to about 0.03 m/s in the deeper waters on the slope. In comparison, tidal models of the region do not fully resolve the slope and exaggerate the increase of tidal currents in shallow water. Attempts to represent the diurnal tidal currents as a trapped wave also show this exaggeration. There was little evidence of internal-wave or internal-tide effects.
A significant finding for subsequent shelf-edge studies was a lateral coherence scale of about 10 km for the currents, comparable with the theoretical Rossby radius of deformation scaling eddies and internal features. This scale gives a basis for future array design. In the temperature field, however, smaller scales were evident from satellite imagery and appeared to contribute a large proportion of the variability. Consequently, a transport balance for temperature (heat) could not be constructed, although movements of the thermocline and changing temperature profiles suggested primarily advective contributions.
Fluctuating contributions to heat flux were calculated from the current meter and thermistor chain records. In common with other locations, eg. north-west of Scotland in 1982-83, these showed a principal contribution along the shelf (to the southwest, against the mean flow) and a small component.