Four-dimensional variational Ocean ReAnalysis
for the western North Pacific

FORA – WNP30

Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and MeteorologicalResearch Institute, Japan Meteorological Agency (JMA/MRI) produced the Four-dimensionalvariational Ocean ReAnalysis for the Western North Pacific over 30 years (FORA-WNP30). It
is the first-ever dataset covering the western North Pacific over three decades at eddy-resolving
resolution. This dataset has 0.1 degree (about 10 km) spatial resolution and provides accurate
estimation of ocean environmental changes around the Japanese Archipelago including a variety of
meso-scale (several tens to several hundreds of km) phenomena, such as eddies, meanders, oceanic
fronts, etc. FORA-WNP30 is a valuable dataset for a variety of oceanographic research topics andpotentially for related fields such as climate study, meteorology, and fisheries.
65N【dataset name】 FORA-WNP30

60N【analysis domain】 15°－ 65°N, 117°E － 160°W【spatial resolution】 0.1°latitude × 0.1°longitude（1/6°east of 160°E and north of 50°N）
vertical 54 layers（0-6300m depth）

55N
50N
45N

【analysis period】 1 Jan. 1982 － 31 Dec. 201440N

【 v a r i a b l e s 】 daily mean values of sea surface height,
potential temperature, salinity,
current velocity (N-S and E-W components),
sea ice concentration

35N
30N

【data format】 NetCDF

25N
20N
15N

Analysis domain of FORA-WNP30
120E

130E

140E

150E

160E

170E

180E 170W 160W

Ocean data assimilation system and ocean observations

The Kuroshio Extension has two distinct
modes: an elongated mode in which thenorthward shift of a strong eastward jet
is accompanied by a strong southern
recirculation gyre, and a contracted modein which the southward shift of a weak jet
is accompanied by a weak recirculation
gyre (Qiu, 2002). FORA-WNP30 has
reproduced the gradual change from theelongated mode of the Kuroshio Extension
in 1992 to the contracted mode. Thismodal transition reversed after 1997 andthe Kuroshio Extension returned to theelongated mode in 2002.

182022°N
3524°N0°E
40151s 50°E

30°N

26145°E0°E

140°E35°N

500 m

1000 m

1500 m10145°E0cm/

14135°E
E40 13°N 0°0m

Spatial distribution of sea
surface temperature (colorshading) and velocity (vector),and vertical cross section ofcurrent velocity along 138°
E inJune 1987, when the Kuroshio
took a large meander path.
Red (blue) in the vertical crosssection depicts eastward(westward), respectively, andcontour interval is 10cm/s.

Monthly mean paths (green lines) of the Kuroshio Extension andsea surface height anomalies (red and blue) during 1986-2005

Time evolution of observations

[°C]
16

FORA-WNP30 is produced bya state-of-the-art 4-dimensionalvariational ocean data assimilation
system, MOVE-4DVAR, developedin JMA/MRI (Usui et al., 2015). The
ocean general circulation model
used in MOVE- 4DVAR is basedon MRI.COM, the ocean model
framework developed in JMA /MRI (Tsujino et al., 2010). All thereanalysis calculation was carriedout on the Earth Simulator with thesupport of JAMSTEC. It is the firstever dataset covering the western
North Pacific over three decades
at eddy-resolving (about 10 km)
resolution. Therefore, the major
ocean current such as the Kuroshio
and Oyashio, and the associatedmeso-scale phenomena such aseddies, fronts, and meanders, arefinely reproduced. In particular,
FORA-WNP30 successfully
reproduces anomalous events
such as the Kuroshio large
meander and anomalous
intrusion of the Oyashio
in 1980s, when there isno satellite altimeter
data.

Interannual variationin theKuroshio Extension

In-situ temperature and salinity profiles above
1500m-depth, gridded sea surface temperature (SST)and satellite altimeter-derived sea surface height (SSH)
are assimilated in FORA-WNP30. The temperatureand salinity profiles are collected from the World Ocean
Database 2013 (WOD13) and the Global Temperature
Salinity Profile Program (GTSPP). The gridded SST is
Merged satellite and in situ Global Daily Sea Surface
Temperature (MGDSST) compiled in Japan Meteorological
Agency (Kurihara et al., 2006). The altimeter-derived SSH
observations are AVISO along-track multimission products
for TOPEX/Poseidon, Jason-1/2, ERS-1/2, Envisat, GFO
and Cryosat-2. The SSH data is available since 1993, andthe number of assimilated observations is closely linked tothe number of satellite data. The number of temperatureand salinity data is almost constant before 2003 but
doubled in 2008 compared to that in 2003, indicating thelarge contribution of Argo floats.

Kuroshio large meander
Figure shows sea surface temperature and velocity fields
south of Honshu Island and the Kuroshio Extension regionin June 1987, when the Kuroshio took a large meander
path. The 3-dimensional structure of the Kuroshio front arefinely captured. In particular, FORA-WNP30 reproduces
the large meander events observed several times in 1980s,
which is an advantage of the dataset.

Southward intrusion of the Oyashio CurrentabaInterannual variation inthe Oyashio area in spring
represented by FORA-WNP30
shows a good agreement withthat from the analysis of Japan
Meteorological Agency (JMA).
FORA-WNP30 illustrates that
the Oyashio water intrudes
southward along the east coasto f H o n s h u Is l a n d a n d t h esouthern tip of the Oyashio
water extends to around 36°N
in March 1984. In contrast, theOyashio area is hardly foundin Kuroshio-Oyashio transition
region in March 2000.
Time series of the Oyashio area in spring (March-May), andspatial distribution of temperature at 100m-depth in March
1984 (the maximum of the Oyashio area) and 2000 (theminimum). Red and black lines denote area calculated from
FORA-WNP30 and JMA analysis. The Oyashio area isdefined by the area of cold water at 100m withtemperature less than 5℃ within 141°
-148°
E and 30°
- 43°
N.

b

Access and use of FORA-WNP30
FORA-WNP30 is now available as a basic ocean reanalysis dataset for widespread fields of climate/ocean research activities. Please refer and accept theterms and conditions of use for FORA-WNP30 described in the following web-site.
If you use this dataset for non-scientific or non-educational purposes, please inform
us (fora_req@jamstec.go.jp) in advance and follow our instructions.

FORA web-site

http://synthesis.jamstec.go.jp/FORA/e/
If you have any questions about FORA dataset,please contact JAMSTEC/CEIST at the e-mail address
fora_req@jamstec.go.jp with your name and affiliation.

Earth Simulator

FORA (4(Four)-dimensional variational Ocean ReAnalysis) – WNP30
Center for Earth Information Science andTechnology (CEIST)Japan Agency for Marine-Earth Science andTechnology (JAMSTEC)

Oceanography and Geochemistry Research
Department
Meteorological Research Institute,Japan Meteorological Agency (JMA/MRI)

3173-25, Showa-machi, Kanazawa-ku, Yokohama,Kanagawa, 236-0001, Japan

http://www.mri-jma.go.jp/index_en.html

http://www.jamstec.go.jp/e/1-1, Nagamine, Tsukuba, Ibaraki, 305-0052, Japan

Published in January 2016