5242 
JOURNAL OF PHYSICAL OCEANOGRAPHY 
VOLUME 50 
(a) Cyclonic 
9 18 — 
10 
5 
si 
120 
m AB 
(b) Non-cyclonic 
5 
ol 
„120 
80 
‚20 
wl. 
x 
»apk-e veloclktv 
2 
100 + 
7 
F' 300 
a 
3 400 
500 
x“ 
„‚‚ranhie velocihr 
BO 
Dr 
420 
00 - 
200 + 
3 300 
5 
= 
8 400 
500 
300 
115 
“4 
be 
105 
u 
KR 
0 40 40 0 40 80 120 
Distance (km) Distance (km) 
FIG. 6. (bottom) Composites of absolute geostrophic velocity (m s*, colors) overlain by potential density 
(kg m”, contours) for the (a) cyclonic and (b) noncyclonic cases. Positive velocities are equatorward. 
The highlighted isopycnal of 27.8 kg m} is the upper boundary of the overflow water. (top) The data coverage. 
‘4 
1.5 
300 
/00 
120 
00 
120 
120 
0.5 
3U 
metric that characterizes the degree to which a given section 
is in the cyclonic state (i.e., the stronger the gradient, the 
more cyclonic, and vice versa). Using the ERAS reanalysis 
wind data, we then created composites of the wind stress curl 
and wind vectors for the two extremes of the velocity gradi- 
ent, in particular the five strongest cases and five weakest 
cases (Fig. 7). The mean wind field during the time of occu- 
sation the sections (see Table 1) go into the composites. In 
:he former, the wind in Denmark Strait is strongly out of the 
aortheast and there is pronounced negative wind stress curl 
over the Blosseville Basin. In the other extreme, the wind is 
weak and variable, while the wind stress curl is weakly pos- 
‘tive over the Blosseville Basin. Väge et al. (2013) showed 
that negative wind stress curl, together with the closed iso- 
3aths of the Blosseville Basin, plays an important role in the 
bifurcation of the EGC at the northern edge of the basin. This 
ın turn would weaken the shelfbreak EGC. Hence. the wind 
stress curl pattern in Fig. 7a is conducive for enhancement of 
:he merged NIJ-separated EGC inthe trough and decreased 
low of the shelfbreak EGC, as seen in the composite of 
Fig. 6a. In the other extreme the wind stress curl would 
weaken the merged flow, consistent with the composite 
of Fig. 6b. 
The wind stress curl forcing, however, does not explain the 
variation in the NIIC between the two states. To address the 
aotential role of the along-strait wind, we employed the along- 
:rack ADT data (Fig. 2 shows the satellite tracks in the region). 
Using the 25 years of ADT data, we computed the cross-track 
zomponent of surface geostrophic velocity for each of the 
‚atellite crossings and projected these to the Lätrabjarg line 
‚see Spall et al. (2019) for details on the methodology]. We 
aote that both the NIIC and merged NIJ-separated EGC 
nave a strong surface signature (while the shelfbreak EGC 
does not, Fig. 4). Next, we created composites of the surface 
a) Strong lateral velocitv aradient 
(b) Weak lateral velocitve nradient 
79 
79a r 
72 Ar 
6001; 
5n 
50c 
56° 
66 
AM 
A207 
A7: 
RY 
50° 
35°Ww 30°W 25°W 20°W 15°W 
FIG. 7. Composites of wind stress curl (X107° N m®, colors) and wind vectors (see the key) for the five extreme 
cases of (a) strong and (b) weak lateral gradients of depth-mean velocity across the Denmark Strait trough. The 
green line denotes the Lätrabjarg transect. The trough is marked by the red star. 
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