Cai, W. J.

Ganachaud, Alexandre

Hu, D. X.

Kessler, W. S.

Sprintall, J.

Horizon / Pleins textes

INTRODUCTION TO
A SPECIAL SECTION
10.1002/2015JC010856
Introduction to special section on Western Pacific Ocean
Circulation and Climate
Dunxin Hu1, Wenju Cai2, Alexandre Ganachaud3, William S. Kessler4, and Janet Sprintall5
1CAS Key Lab of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China,
2Commonwealth Scientiﬁc and Industrial Research Organization, Melbourne, Victoria, Australia, 3Institut de Recherche
pour le Developpement, LEGOS, UMR5566 CNRS-CNES-IRD-Universite de Toulouse III, Toulouse, France, 4NOAA/Paciﬁc
Marine Environmental Laboratory, NOAA/PMEL/OCRD, Seattle, Washington, USA, 5Scripps Institution of Oceanography,
University of California, San Diego, La Jolla, California, USA
The western Paciﬁc Ocean (WPO) is a cross road and a major pathway whereby different water masses con-
verge or traverse from mid-latitude and high-latitude to adjacent oceans and ambient marginal seas. One
protruding feature of the WPO is the warm pool, the world’s warmest open ocean surface water spanning
the northern and southern tropical WPO. The warm pool modulates global and regional climate systems,
including the El Ni~no-Southern Oscillation (ENSO) and the Asian and Australian monsoon. The other feature
is the Western Boundary Current (WBC) system, which consists of the Kuroshio and the East Australian Cur-
rent, and, uniquely, two equatorward low-latitude WBCs, the Mindanao Current in the North Paciﬁc, and
Gulf of Papua Current/New Guinea Coastal Current system in the South. These two features are closely
linked; a recharge or discharge of the warm pool triggers a response of the WBCs, and variability of the
WBCs in turn modulates the evolution of the warm pool.
This special section on Western Paciﬁc Ocean Circulation and Climate of the Journal of Geophysical Research
assembles 31 research papers, mainly presented at the Open Science Symposium on Western Paciﬁc Ocean Cir-
culation and Climate held on 15–17 October 2012 in Qingdao, China, under the auspices of the Northwestern
Paciﬁc Ocean Circulation and Climate Experiment (NPOCE) [Hu et al., 2011] and Southwest Paciﬁc Ocean Circu-
lation and Climate Experiment (SPICE) [Ganachaud et al., 2007]. The goal of this inaugural symposium was to
provide a forum for scientists to exchange the latest knowledge pertaining to the WPO circulation and cli-
mate. The presentations consisted of 6 keynote talks, 11 invited talks, 40 contributed talks, and 73 poster pre-
sentations, covering a wide range of important areas, including dynamics and variability of the WBCs, their
interaction with the ambient circulation, roles of the WPO circulation in variability of the warm pool and
ENSO, in regional climatic systems (e.g., monsoon, typhoon, and extreme climatic events) and their predict-
ability, and in carbon cycle, biogeochemical process, acidiﬁcation, ecosystem, and paleooceanography.
Included in this special section are 31 research articles documenting the latest progress in our understand-
ing of the WPO, including the Paciﬁc basin-scale circulation, the Indonesian throughﬂow (ITF), Asian mon-
soon, and climate change in the Paciﬁc Ocean. A considerable body of the results is based on in-situ data,
remote sensing, and numerical models, which contribute to the NPOCE, SPICE, and ITF studies. As such, the
results presented in this special section attest to the effectiveness and success of these international pro-
grams. Some highlights are presented below, as a taster.
In the northwest Paciﬁc, signiﬁcant progress has been made toward understanding the WBC and this
includes a depiction, based mainly on in situ current measurements, of the Mindanao Undercurrent, the
Luzon Undercurrent, and their connection with the North Equatorial Undercurrent. The latest result veriﬁes
the existence of the Mindanao Undercurrent, which features a core centered at around 900 m, some 300 m
deeper than previously estimated using geostrophic balance. The strong intraseasonal variability and
intense interactions of the Mindanao Undercurrent with the Luzon Undercurrent and the North Equatorial
Undercurrent were also previously poorly appreciated. Another advance lies in our improved understanding
of decadal variability of the North Equatorial Current bifurcation, which shows a southward shift of its lati-
tude after the 1998/1999 La Ni~na event, contributing to the North Paciﬁc regime shift.
In the South Paciﬁc, knowledge of the Southwest Paciﬁc circulation, including ocean circulations of the
Coral, Solomon, and Tasman seas, has been substantially improved. These include a new depiction of two
Special Section:
Western Pacific Ocean
Circulation and Climate
Correspondence to:
D. Hu,
dxhu@ms.qdio.ac.cn
Citation:
Hu, D., W. Cai, A. Ganachaud,
W. S. Kessler, and J. Sprintall (2015),
Introduction to special section on
Western Paciﬁc Ocean Circulation and
Climate, J. Geophys. Res. Oceans, 120,
3175–3176, doi:10.1002/
2015JC010856.
Received 20 MAR 2015
Accepted 27 MAR 2015
Accepted article online 10 APR 2015
Published online 5 MAY 2015
VC 2015. American Geophysical Union.
All Rights Reserved.
HU ET AL. INTRODUCTION TO WPOCC SS 3175
Journal of Geophysical Research: Oceans
PUBLICATIONS
South Equatorial Current branches that enter the Coral Sea between New Caledonia and the Solomon
Islands, form jets, feed the Gulf of Papua Current against Australia, and ﬂow into the Solomon Sea in the
New Guinea Coastal Current system. During this long transit, waters are found to be enriched through land-
ocean boundary exchanges, inducing downstream consequences such as iron fertilization. Another high-
light is that showed from the recent mooring measurements, the East Australian Current feeding ﬁlaments
such as the Tasman Front is weaker than previously thought.
In the ITF research area, a reconstructed 18-year transport time series shows that the partitioning of the
total ITF transport through each of the major outﬂow passages (Lombok, Ombai, and Timor) varies accord-
ing to the phase of the Indian Ocean Dipole and ENSO. Further, in situ observations show coherent intrasea-
sonal (30–70 days) variations, with the eastern equatorial Indian Ocean leading the Lombok and Ombai
Straits.
Analyses of basin-scale processes produce many interesting results, including an anticorrelation of the WBC
with the Subtropical Cells, and coherent variations of meridional transports at 32S with the Southern Annu-
lar Mode. On smaller scales, the Halmahera and Mindanao Eddies and eddies in the Solomon Sea were
investigated in terms of their generation, structure, and propagation using observations, high-resolution
numerical simulations, and altimetric data. In particular, eddies in the Solomon Sea show a strong seasonal
and interannual modulation with maximum activities in June and/or during La Ni~na events.
In addition to observation-based analyses, coupled ocean-atmosphere models were deployed to elucidate
important processes, particularly those for which sufﬁcient data are still not available, such as salinity evolu-
tion, vertical distribution of wind energy, and impact of the warm pool and ENSO on Asian monsoons. One
highlight is that in the Solomon Sea, WBC advection, upwelling, and river discharge emerge as identiﬁable
processes that even in a small region could affect salinity on seasonal time scales. Another is that in the Kur-
oshio region, wind-induced energy on near-inertial time scales could penetrate down to 3000 m and con-
tribute to deep-ocean mixing. Further, the conclusion that heat content of the warm pool is a predictor of
the South China Sea summer monsoon is reafﬁrmed, even on decadal time scales; likewise, the relationship
between ENSO and the East Asian Winter Monsoon is conﬁrmed to ﬂuctuate substantially on decadal time
scales.
Finally, comprehensive coupled ocean-atmosphere models were also deployed to provide a window to
future WBC changes. For example, during the twentieth century, Antarctic ozone depletion and increasing
greenhouse gases conspired to generate a conspicuous poleward intensiﬁcation of the mid-latitude positive
wind stress curl and hence the Southern Hemisphere oceanic supergyre. The Antarctic ozone is projected
to recover by 2045, which, by and large, offsets the effect of increasing greenhouse gases before 2045, but
thereafter the poleward intensiﬁcation is modeled to resume and accelerate. This intensiﬁcation implies a
southward inﬂuence of warm subtropical East Australian Current waters into the western Tasman Sea,
where warming has been observed to proceed at a rate about four times of the global average.
In summary, articles to this special section provide an overview of the latest science in the western Paciﬁc
ocean circulation and climate, identify research issues to be targeted, and raise questions to be resolved, in
future endeavor through observations, process studies, and modeling. The guest editors thank all authors
for their timely contribution. Especially, we are obliged to the AGU publication staff, editors, and reviewers
for their unremitting work for this special section.
References
Hu, D., et al. (2011), Northwestern Paciﬁc Ocean Circulation and Climate Experiment (NPOCE), China Ocean Press, Beijing, China.
Ganachaud, A., et al. (2007), Southwest Paciﬁc Ocean Circulation and Climate Experiment (SPICE)—Part I. Scientiﬁc Background, CLIVAR
Publ. Ser., 111, NOAA OAR special report, NOAA/OAR/PMEL, 37 pp., Seattle, Wash.
Journal of Geophysical Research: Oceans 10.1002/2015JC010856
HU ET AL. INTRODUCTION TO WPOCC SS 3176


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