December 2024 | Oceanography
from satellite altimetry was selected as
the study site (Figure 1). Te particu-
lar dipole targeted was identifed in the
weeks prior to the onset of the cruise. Te
study consisted of several weeks of direct
measurements from R/V Neil Armstrong
augmented by a large number of auton-
omous systems, including drifers, a
Wirewalker, and uncrewed underwater
vehicle (UUV) gliders (Figure 2). Te
cyclone/ anticyclone dipole pair was asso-
ciated with negative dynamic height
and cold surface water on the cyclonic
(counterclockwise circulating) side and
positive dynamics height and warm water
surface waters on the anticyclonic (clock-
wise circulating) side. Te study period
was characterized by extremely deep
mixed layers on the cyclonic side of the
dipole and winds that generally remained
above 10 m s–1. Te passage of a series of
atmospheric cyclones with strong winds
and high sea states (Figure 3) forced
episodic rapid deepening of the sur-
face boundary layer (Klenz et al., 2022).
Surface cooling was generally unim-
portant, but the Stokes forcing played a
leading- order role in mixed and turbu-
lent boundary layer deepening (Figure 3;
Skyllingstad et al., 2023).
Te fndings from the pilot study moti-
vated the larger 2019 study of a similar
dipole at almost the same site (Figure 2),
which again utilized R/V Neil Armstrong
along with profling foats (Kunze et al.,
2023; Girton et al., 2024, in this issue),
uncrewed surface vehicle (USV) Wave
Gliders, gliders, surface drifers, and
moorings (Voet et al., 2024, in this issue).
Tis range of resources allowed the team
to examine the properties of near- inertial
response in both cyclonic and anti-
cyclonic fows (Tomas et al., 2020, 2023;
and 2024a, 2024b, both in this issue). Te
2019 program consisted of four mod-
ules: (1) “jet + confuence,” that exam-
ined the evolution of inertial oscillations
(35 kts wind event) in strong cyclonic
and anticyclonic vorticity, (2) “sheepdog”
with a drifing array in a quieter region,
(3) a mapping survey, and (4) “fence” and
“greyhound” to sample the inertial wave
feld at the edge of an anticyclonic eddy
with strong submesoscale gradients in a
strong frontal region (Figure 4).
A second full-scale process cruise
planned for 2020 was scaled back due to
the Covid pandemic and reoriented to
focus on mooring recovery with a min-
imal autonomous presence. With the
loss of ship time, the focus of the study
shifed closer to Iceland, north of the
North Atlantic Current frontal system,
with measurements made during the
September to November period using
drifers, foats, and USV and UUV glid-
ers (Figure 2a). Te 2020 efort also fea-
tured an Air-Launched Autonomous
Micro-Observer profling foat and a spar
buoy system (Zimmerman et al., 2024, in
this issue) that measured the enhanced
near-inertial forcing and breakdown of
summer surface stratifcation caused by
the passage of an extratropical cyclone.
FIGURE 1. Track of R/V Neil
Armstrong (heavy black line).
Drifter tracks are colored by sea
surface temperature. They are
overlaid by satellite dynamic
topography (absolute dynamic
topography [ADT] from EU
Copernicus Marine Service,
https:// doi.org/ 10.48670/ moi-
00148), with negative ADT
(cold surface waters) indicated
by dashed contours and posi-
tive ADT (warm surface waters)
indicated by solid contours.
FIGURE 2. (a) Autonomous assets
used during the Near-Inertial Shear
and Kinetic Energy in the North
Atlantic
experiment
(NISKINe),
2018–2021. While the focus of the
experiment was on the vorticity
associated with the North Atlantic
Current Extension, other observa-
tional eforts centered on the role
of the near-inertial response above
the Reykjanes Ridge and along
the margin of the Icelandic Basin.
(b) R/V Neil Armstrong tracks in
support of NISKINe, 2018–2019.
The 2020 field efort was also
orchestrated using a combination
of chartered vessels and the sup-
port of the Icelandic Coast Guard.