On the Nature and Variability of the East Greenland Spill Jet: A Case Study in Summer 2003*

Abstract

Results from a high-resolution (;2 km) numerical simulation of the Irminger Basin during summer 2003 are presented. The focus is on the East Greenland Spill Jet, a recently discovered component of the circulation in the basin. The simulation compares well with observations of surface fields, the Denmark Strait overflow (DSO), and the hydrographic structure of typical sections in the basin. The model reveals new aspects of the circulation on scales of O(0.1-10) days and O(1-100) km.The model Spill Jet results from the cascade of dense waters over the East Greenland shelf. Spilling can occur in various locations southwest of the strait, and it is present throughout the simulation but exhibits large variations on periods of O(0.1-10) days. The Spill Jet sometimes cannot be distinguished in the velocity field from surface eddies or from the DSO. The vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term.The average model Spill Jet transport is 4.9 61.7 Sv (1 Sv [ 10 6 m 3 s 21 ) equatorward, about 2½ times larger than has been previously reported from a single ship transect in August 2001. Kinematic analysis of the model results suggests two different types of spilling events. In the first case (type I), a local perturbation results in dense waters descending over the shelf break into the Irminger Basin. In the second case (type II), surface cyclones associated with DSO deep domes initiate the spilling process. During summer 2003, more than half of the largest Spill Jet transport values are of type II.

Moored observations of shelfbreak processes at the inflow to and outflow from the Arctic Ocean

“…In fact, it is reduced about half of the geostrophic velocity. As pointed out in Section 3.4, this may explain the difference of a factor of approximately two between the velocities reported in Brearley et al (2012) and Magaldi et al (2011).…”

“…The Spill Jet hypothesis discussed in Pickart et al (2005a) and Magaldi et al (2011) can explain the asymmetry in the eddy shape observed at EG5. As the leading edge of the eddy moves along the slope, the offshore velocity component draws water off the shelf.…”

“…A numerical model study of the region found that DSOW cyclones also lead to spilling of dense water off the shelf (Magaldi et al, 2011). The cyclones are associated with strong offshore velocities on their leading edge that pull the water off the shelf.…”

“…A regional numerical model study investigating the circulation along the East Greenland slope in general, and near the mooring array site in particular, is reported in Magaldi et al (2011). The time period of the numerical study is summer 2003.…”

“…Magaldi et al (2011) suggested that the spilling of this water off the shelf may be due to the passage of DSOW cyclones (termed Type II events) or due to generic instabilities or small scale variability in the vicinity of the shelfbreak (termed Type I events). Here we present evidence for the two different types of spilling events.…”