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December 2024 | Oceanography

PROGRESS

NISKINe

THE NEAR-INERTIAL SHEAR AND KINETIC ENERGY

IN THE NORTH ATLANTIC EXPERIMENT

THE OFFICIAL MAGAZINE OF THE OCEANOGRAPHY SOCIETY

VOL. 37, NO. 4, DECEMBER 2024

Oceanography

Oceanography | Vol. 37, No. 4

POWERING

DECISIONS

WWW.SEABIRD.COM

ALWAYS WATCHING THE HORIZON

FOR A

BETTER

OCEAN.

December 2024 | Oceanography

contents VOL. 37, NO. 4, DECEMBER 2024

SPECIAL ISSUE ON NISKINe

6 Introduction

By H.L. Simmons, L. St. Laurent, L. Rainville, and L. Thomas

10 Why Near-Inertial Waves Are Less Afected by Vorticity in the Northeast

Paciﬁc Than in the North Atlantic

By L.N. Thomas, S.M. Kelly, T. Klenz, W.R. Young, L. Rainville, H.L. Simmons, V. Hormann,

and I. Stokes

22 Blocked Drainpipes and Smoking Chimneys: Discovery of New Near-Inertial

Wave Phenomena in Anticyclones

By L.N. Thomas, J.N. Moum, L. Qu, J.P. Hilditch, E. Kunze, L. Rainville, and C.M. Lee

34 Near-Inertial Energy Variability in a Strong Mesoscale Eddy Field in the

Iceland Basin

By G. Voet, A.F. Waterhouse, A. Savage, E. Kunze, J.A. MacKinnon, M.H. Alford, J.A. Colosi,

H.L. Simmons, T. Klenz, S.M. Kelly, J.N. Moum, C.B. Whalen, R.-C. Lien, and J.B. Girton

48 Observations of the Upper Ocean from Autonomous Platforms During the

Passage of Extratropical Cyclone Epsilon (2020)

By M.T. Zimmerman, S.R. Jayne, L. Rainville, C.M. Lee, J.M. Toole, J.B. Edson, C.A. Clayson,

A.K. Ekholm, and C.R. Densmore

58 Coherent Float Arrays for Near-Inertial Wave Studies

By J.B. Girton, C.B. Whalen, R.-C. Lien, and E. Kunze

68 Interaction of Typhoon-Driven Near-Inertial Waves with an Anticyclone in the

Philippine Sea

By C.Z. Lazaneo, L. Thomas, Z.B. Szuts, J.M. Cusack, K.-F. Chang, and R.K. Shearman

DEPARTMENTS

5 QUARTERDECK. International Cooperation Enriched the Near-Inertial Shear

and Kinetic Energy in the North Atlantic Experiment

By L. Centurioni and T. Paluszkiewicz

82 WORKSHOP REPORT. Observing Ocean Boundary Currents: Lessons

Learned from Six Regions with Mature Observational and Modeling Systems

By N.K. Ayoub, M.P. Chidichimo, E. Dever, X. Guo, S.Y. Kim, M. Krug, B.M. Míguez, T. Morris,

M. Roughan, J. Sprintall, K. Tanaka, R.E. Todd, J. Wilkin, E. Álvarez-Fanjul, M. Andres,

A. Bosse, C.A. Edwards, J. Gula, C.G. Kerry, Y. Miyazawa, P. Oddo, E. Oka, and K.D. Zaba

92 THE OCEANOGRAPHY CLASSROOM. Supporting Sensemaking by

Introducing a Connecting Thread Throughout a Course

By K. Daae, S. Semper, and M.S. Glessmer

95 FROM THE TOS JEDI COMMITTEE. Recognizing JEDI Eforts in the Hiring,

Tenure, and Promotion Process

By J. Pierson, G. Nesslage, A. Fries, H. Kelsey, F. Chen, C. Davis, and K. Rose

97 CAREER PROFILES. Emma R. Ozanich, Project Scientist and Acoustic

Modeler, JASCO Applied Sciences • Cassaundra Rose, Policy Advisor, Natural

and Working Lands, US Climate Alliance

December 2024 | Oceanography

Oceanography | Vol. 37, No. 4

ON THE COVER

Photo of a Wirewalker deployment from

R/V Armstrong taken during a 2018 cruise sup-

porting the Near-Inertial Shear and Kinetic

Energy in the North Atlantic Experiment

(NISKINe). Photo credit: San Nguyen, Scripps

Institution of Oceanography

SPECIAL ISSUE GUEST EDITORS

Harper L. Simmons, University of Washington

Leif Thomas, Stanford University

The Oceanography Society

1 Research Court, Suite 450-117

Rockville, MD 20850 USA

t: (1) 301-251-7708

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CORRECTIONS

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Digital versions of articles will be updated.

In May 2024, members of The Oceanography Society (TOS) Council and staf

met to develop a new mission statement and strategic plan for the Society.

MISSION. To build the capacity of its diverse global membership; catalyze

interdisciplinary ocean research, technology, policy, and education; and

promote equitable access to opportunities for all.

In support of the mission, the TOS Council defned goals in three areas to

advance during the period encompassed by the plan:

• Develop Policy for Science and Science for Policy

• Serve a Broader Ocean Science Community

• Support Undergraduate and Graduate Students

Read the full strategic plan at tos.org/tos-strategic-plan

THE OCEANOGRAPHY SOCIETY’S

NEW MISSION STATEMENT

AND STRATEGIC PLAN

Image credit: NASA Ocean Color Image Gallery, colors enhanced by Patrick C. Gray

December 2024 | Oceanography

tos.org

EDITOR

Ellen S. Kappel, Geosciences Professional Services Inc.

ASSISTANT EDITOR

Vicky Cullen

DESIGN/PRODUCTION

Johanna Adams

ASSOCIATE EDITORS

Claudia Benitez-Nelson, University of South Carolina

Luca Centurioni, Scripps Institution of Oceanography

Grace Chang, Integral Consulting Inc.

Tim Conway, University of South Florida

Kjersti Daae, University of Bergen

Mirjam S. Glessmer, Lund University

Charles H. Greene, University of Washington

Alistair Hobday, CSIRO Environment

Carol Robinson, University of East Anglia

Amelia Shevenell, University of South Florida

Robert E. Todd, Woods Hole Oceanographic Institution

Peter Wadhams, University of Cambridge

Oceanography contains peer-reviewed articles that chronicle

all aspects of ocean science and its applications. The journal

presents signiﬁcant research, noteworthy achievements, excit-

ing new technology, and articles that address public policy and

education and how they are afected by science and technol-

ogy. The overall goal of Oceanography is cross- disciplinary

communication in the ocean sciences.

Oceanography (Print ISSN 1042-8275; Online ISSN 2377-617X)

is published by The Oceanography Society, 1 Research Court,

Suite 450-117, Rockville, MD 20850 USA. Oceanography arti-

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Oceanography

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The Oceanography Society was founded in 1988 to advance

oceanographic research, technology, and education, and

to disseminate knowledge of oceanography and its appli-

cation through research and education. TOS promotes the

broad understanding of oceanography, facilitates consen-

sus building across all the disciplines of the ﬁeld, and informs

the public about ocean research, innovative technology,

and educational opportunities throughout the spectrum of

oceanographic inquiry.

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PRESIDENT: Deborah Bronk

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COUNCILORS

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EDUCATION: Leilani Arthurs

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JUSTICE, EQUITY, DIVERSITY, AND INCLUSION: Sheri White

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December 2024 | Oceanography

Oceanography | Vol. 37, No. 4

THE OCEANOGRAPHY SOCIETY’S

HONORS PROGRAM

One of the most meaningful aspects of being a member of

The Oceanography Society (TOS) is the opportunity to recog-

nize and celebrate our colleagues’ accomplishments. Please

take this opportunity to recognize a colleague, mentor, team,

or peer for their exceptional achievements and contributions

to the ocean sciences.

Medals

WALLACE S. BROECKER MEDAL is awarded biennially

to an individual for innovative and impactful contributions to

the advancement or application of marine geoscience, chem-

ical oceanography, or paleoceanography. Nomination dead-

line: October 31, 2025.

The NILS GUNNAR JERLOV MEDAL is awarded bien-

nially to an individual for advancing our knowledge of

how light interacts with the ocean. Nomination deadline:

October 31, 2025.

The WALTER MUNK MEDAL is awarded biennially to

an individual for extraordinary accomplishments and novel

insights contributing to the advancement or application of

physical oceanography, ocean acoustics, or marine geophys-

ics. Nomination deadline: October 31, 2025.

The MARY SEARS MEDAL is awarded biennially to an

individual for innovative, and impactful contributions to the

advancement or application of biological oceanography,

marine biology, or marine ecology, along with outstand-

ing contributions to education and mentorship in the feld.

Nomination deadline: October 31, 2025.

Fellows

Recognizing TOS members who have made outstanding

and sustained contributions to the feld of oceanography

through scientifc excellence, extraordinary service and lead-

ership, and/or strategic development of the feld. Nomination

deadline: October 31, 2025.

Awards

The TOS EARLY CAREER AWARD is presented bienni-

ally to up to three TOS Early Career members for signifcant

early- career research contributions and impact, and the

potential for future achievements in the feld of oceanogra-

phy. Nomination deadline: October 31, 2025.

The TOS MENTORING AWARD is given biennially to an

individual for excellence and/or innovation in mentoring the

next generation. Nomination deadline: October 31, 2025.

The TOS OCEAN OBSERVING TEAM AWARD is pre-

sented biennially to a team for innovation and excellence in

sustained ocean observing for scientifc and practical appli-

cations. Nomination deadline: October 31, 2025.

tos.org/honors

December 2024 | Oceanography

A critical part of launching an intensive physical oceanography

feld campaign is identifying the appropriate patch of ocean—

the area where the process you wish to study dependably occurs

and has maximum impact. Early explorations and publica-

tions helped establish the region of Iceland as the ideal candi-

date for the US Ofce of Naval Research Departmental Research

Initiative, the Near-Inertial Shear and Kinetic Energy in the

North Atlantic Experiment (NISKINe). As the NISKINe group

organized the experiment, the local Icelandic marine science

community’s expertise was of principal importance in formulat-

ing specifcs of its timing, location, and component interactions.

International feld programs are so much more enlightening

and fulflling when we learn from one another and gain under-

standing of new cultures and ways of looking at science. Te

friendships and colleagueships that were initiated as a result of

NISKINe continue to grow and contribute to the international

ocean science community’s capacity. We are grateful to our

colleagues at the Icelandic Marine and Fresh Water Institute,

the Icelandic Coast Guard, the Meteorological Ofce, and the

University of Iceland for their hospitality, guidance, and shared

contributions that made this program a success.

AUTHORS

Luca Centurioni (lcenturioni@ucsd.edu) is Associate Editor, Oceanography, and

Director, Lagrangian Drifter Laboratory, Scripps Institution of Oceanography,

La Jolla, CA, USA. Terri Paluszkiewicz is President, Octopus Ocean Consulting

LLC, VA, USA.

ARTICLE DOI

https://doi.org/10.5670/oceanog.2024.310

QUARTERDECK

INTERNATIONAL COOPERATION

ENRICHED THE NEAR-INERTIAL SHEAR AND KINETIC

ENERGY IN THE NORTH ATLANTIC EXPERIMENT

By Luca Centurioni and Terri Paluszkiewicz

Oceanography Flipbooks

https://oceanography.publuu.com

Be sure to visit the open access Oceanography ﬂipbook library to

page through the full NISKINe special issue. While there, explore other

Oceanography issues back to March 2015.

AUTHORS! Flipbooks are an exciting enhancement to Oceanography.

In these ﬂipbooks, we can embed videos, animations, photo galleries,

and audio ﬁles in your article. For details on ﬁle sizes and formats, visit

https://tos.org/oceanography/guidelines.

Oceanography | Vol. 37, No. 4

INTRODUCTION

Near-inertial internal waves (NIW)

constitute a dominant mode of high-

frequency variability in the ocean’s inte-

rior, comprising about half the kinetic

energy in the ocean at most sites (and

even more in the winter beneath storm

tracks; Alford et al., 2016). Over the last

decade there has been a signifcant focus

in the physical oceanographic commu-

nity on internal tides, which produce large

thermocline displacements, afect sound

propagation, and control some hotspots

of elevated turbulent mixing. Near-

inertial internal gravity waves, which are

primarily generated not by tides but by

winds, are of similar importance, provid-

ing comparable kinetic energy and the

vast majority of the shear variance, and

likely leading to a substantial amount of

turbulent mixing. Signifcant defciencies

remain in our understanding of the phys-

ical processes that determine their gener-

ation, evolution, and destruction.

No existing regional or global numer-

ical models fully account for the gener-

ation, radiation, and breaking of NIWs,

largely because of the need for high reso-

lution to resolve the high-mode structure

and because the physics is not sufciently

understood. Te NIW problem has been

difcult to address, partially due to the

episodic nature of wind generation and

the nonlinear physics involved. Te sem-

inal experimental study of NIWs was the

Ocean Storms Experiment (OSE), which

took place in the late 1980s (D’Asaro

et al., 1995). Te main focus of the OSE

was on the larger-scale lateral structure of

NIWs, which theory predicts is shaped by

Earth’s curvature through the so-called

beta efect (Gill, 1984). During the OSE,

the role of the beta efect in leading to the

initial growth of horizontal gradients in

the NIW feld was clearly demonstrated,

leading to a qualitative agreement with

theory. However, the theory could not

reproduce the observed “beam,” wherein

energy migrated quickly downward with

time from the mixed layer following

storm events. An important consequence

is that neither the decay of mixed-layer

motions nor the rate of energy transfer

into the deep ocean can adequately be

predicted for the best-documented storm

response on record. Tis conundrum

has remained for the past 35 years since

these data were collected, in part because

the OSE data lacked sufcient vertical

and horizontal resolution to quantify the

detailed structures of the NIWs and their

evolution. Moreover, the vital question of

the distribution of mixing by the NIWs

was unaddressed by the OSE.

Motivated by these questions, in 2016

the US Ofce of Naval Research spon-

sored the Near-Inertial Shear and Kinetic

Energy in the North Atlantic experiment

(NISKINe). Te objective was to exam-

ine how NIWs rapidly radiate out of the

mixed layer by developing smaller-scale

horizontal structures through interaction

with ocean eddies and how NIWs gener-

ate turbulence and mixing. Conducted

in the eddy-rich, stormy North Atlantic

during certain periods from 2018 to 2020,

NISKINe utilized conceptualized studies,

numerical modeling, and the latest tech-

nology to make direct, high-resolution

observations of the NIW feld to examine

the physics. Here, we describe some high-

lights of the multi-year study and intro-

duce a collection of articles that elaborate

on the fndings.

NISKINe

NISKINe combined observational, mod-

eling, and theoretical approaches to

underpin the at-sea science. Te program

integrated results from three feld years

in the Iceland Basin: a 2018 pilot study,

a 2019 full-scale deployment, and a mod-

est (pandemic impacted) efort in 2020.

Tese data collection eforts were central

to NISKINe, as they formed the basis for

theoretical and process-oriented model-

ing eforts. Process-oriented studies that

addressed NIW generation, NIW-eddy

interactions, and the role of surface waves

in afecting the energy input to NIWs

included those by Asselin and Young

(2020), Asselin et al. (2020), Barkan

et al. (2021), Skyllingstad et al. (2023),

and Stokes et al. (2024). Tese detailed

works were framed by studies utilizing

global ocean models for broader under-

standing of NIW signifcance including

Arbic et al. (2022), Raja et al. (2022), and

Yang et al. (2023).

For the 2018 pilot experiment, a

dipole in the Icelandic Basin identifed

INTRODUCTION

THE NEAR-INERTIAL SHEAR AND KINETIC ENERGY

IN THE NORTH ATLANTIC EXPERIMENT

By Harper L. Simmons, Louis St. Laurent, Luc Rainville, and Leif Thomas

INTRODUCTION TO THE

SPECIAL ISSUE ON NISKINe

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.

Oceanography | Vol. 37, No. 4

FIGURE 3. UUV sampling during the 2018 pilot experiment. The left panels are temperature and salinity from Seaglider 124, with mixed layer depth indi-

cated. Wind and wave conditions (top right panels) and upper ocean turbulent dissipation rate (lower right panel) from Slocum glider “Husker” over the

course of several strong storms during the cruise period. White dots indicate mixed layer depth, and the contours indicate the ε = 10–9 and 10–7 W kg–1

dissipation levels. See also Figure 2.

SUMMARY AND DISCUSSION

During the multiple years of the NISKINe

program, an extraordinary number

of autonomous assets were employed

(Figure 2a). Te NISKINe study may be

among the largest collective deployments

of autonomous assets for a single pro-

gram. Tis focused use of autonomous

assets was particularly helpful in 2020,

when the Covid pandemic signifcantly

impacted the availability of ship-based

sampling. Together with ship sampling

and moorings, autonomous platforms

captured processes happening on many

diferent temporal and spatial scales that

are fundamental to understanding the

evolution of near-inertial waves.

While results from the NISKINe study

are still being assessed and written up, a

clear outcome of the program is a better

understanding of the signifcant role that

vorticity plays in moderating the input

and subsequent cascade of near-inertial

energy and shear into the ocean interior.

Such NIW-eddy interactions are high-

lighted in this special issue (e.g., Tomas

et al., 2024a). Te coupling of the atmo-

spheric storm track with enhanced

oceanic vorticity in the region of the

North Atlantic Current distinguishes

FIGURE 4. Sampling modules during the 2019 process cruise. The cruise track, colored by abso-

lute sea surface salinity, is overlaid upon contours of dynamic topography (2 cm intervals). The color

scale for salinity, the same for all panels, shows the details of the frontal stratiﬁcation that character-

izes the submesoscale dynamics of the ﬂow. Modules 1–4 are described in the text.

-28°

-26°

-24°

-22°

-20°

57°

58°

59°

60°

61°

35.1

35.15

35.2

35.25

35.3 g/kg

sea surface

absolute salinity

29 May 1400 to 06 Jun 0800

05 Jun 0800 to 08 Jun 0100

57°40’

57°50’

57°30’

57°20’

57°00’

24°00’

23°30’

24°30’

23°00’

22°00’

23°30’

22°30’

22°00’

21°00’

20°30’

22°30’

21°30’

24°00’

23°00’

22°30’

23°30’

57°10’

57°30’

57°20’

57°10’

58°10’

58°00’

57°50’

58°10’

58°20’

58°30’

58°40’

58°00’

58°10’

58°20’

58°30’

58°40’

58°50’

58°00’

08 Jun 0400 to 09 Jun 1500

09 Jun 1500 to 15 Jun 2100

20 km

confluence

jet

sheepdog

100 km

moorings

greyhound

deployment

array #2

deployment

array #3

deployment

array #1

fence

CTDs

uCTD

20 May

27 May

03 Jun

10 Jun

17 Jun

24 Jun

01 Jul

200

400

600

800

1000

depth [m]

34.9

35.1

35.2

35.3

35.4

35.5 psu

MLD

100

150

200

250

300

350

400

450

500

550

600 650

700 km

cumulative distance along track

20 May

27 May

03 Jun

10 Jun

17 Jun

24 Jun

01 Jul

200

400

600

800

1000

depth [m]

12°C

MLD

19 May

100

120

140

160

180

200

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

21 May

23 May

25 May

27 May

Depth (m)

u10