Monthly to annual variability of the Norwegian Atlantic slope current: connection between the northern North Atlantic and the Norwegian Sea

Abstract

This study investigated relations between direct current measurements in the Norwegian Atlantic slope current (NwASC), the sea surface height variability from the TOPEX altimeter, and reanalysed mean sea level pressure fields. The analyses show significant coherence between the leading mslp and ssh EOF modes of variability, and again these modes are significantly coherent with variability in the NwASC for periods of a few months to 6 months. There is also some indication that similar relation is also valid for the annual scale. The underlying physical process, inferred from the temporal evolution and spatial structure, is that variability in the westerly winds modulates the sea level slope from the northern North Atlantic into the Norwegian Sea, and thus provide a barotropic force to the Norwegian Sea. Furthermore, increased westerlies occur in phase with a steepening of the generally downward sea level slope, and this also coincides with increased NwASC. A generalized Sverdrup balance allows the observed variability in the sea level slope along the NwASC to be related to the local variability in the wind stress curl.