Analysis of Near Surface Circulation of the Japan East Sea
Pearn P. Niiler
Scripps Institution of Oceanography
9500 Gilman Drive
MC 0213
La Jolla, CA 92093
Phone: (858) 534-0378 fax: (858) 534-7931 email: pniiler@ucsd.edu
Dong-Kyu Lee
Department of Marine Sciences, Busan National University
Busan, 609-735, Korea
Phone: (51)510-2180 Fax: (51)581-2963 email: lee@east.ocean.pusan.ac.kr
PROJECT GOALS
The project goal is to study the variability of the upper ocean current systems and their relationship to
meteorological forcing. To this end, spatially coherent field observations are required of the ocean
response and the atmospheric forcing. A new instrument, the MINIMET, a water following drifter,
was designed as a tool to obtain ocean and atmospheric data. Arrays of MINIMETS will be utilized in
a coordinated field experiment in marginal seas to study wind-driven ocean currents.
OBJECTIVES
The scientific objectives are to obtain direct measurements of ocean circulation on various time and
space scales that are of sufficient spatial density and time duration so both seasonal means and intraseasonal variations can be determined. This data is used to test model dynamics, both in the processes
that determine the mean motions, as well as the exchange of energy and momentum between the mean
and the eddies.
APPROACH
In marginal seas, circulation patterns are spatially complex and seasonably variable. Lagrangian
techniques are well suited for developing quantitative estimates of the circulation in the areas where
the general pattern of currents are not well known. Wind fields are complex, often affected by
mountains or other land boundaries. Large numbers of drifters were deployed from volunteer ships in
the Japan-East Sea to map the circulation patterns. In the period of 1998-2001 we released 56
MINIMETs and 33 SVP drifters from VOS and research vessels. In addition to drifters deployed by
this project, 137 drifter data are used for analysis. Data from the QuikSCAT was used for verification
of the wind observations.
WORK COMPLETED
Data processing has been completed from a uniform format from a suite of 131 SVP, 44 MINIMET
and 72 NAVY drifters. Data from QuikSCAT has been interpolated on to the drifter tracks and the co-
located data has been analyzed. The analyses and dynamical interpretations of drifter tracks with
satellite altimeter data have been completed.
RESULTS
From drifters and the historical file of temperature at a depth of 100 m, 15m depth circulation and
its variances in relationship to the seasonal mean warm and cold water regions were constructed on
0.5 resolutions. The strongest seasonal currents were: the East Korean Warm Current (EKWC), the
Tsushima Current (TC), the North Korean Cold Current (NKCC) and local eastwards intensifications
along the sub-polar frontal patterns. The TC and NKCC were observed during summer and drifters
passed through the Soya Strait only in summer. The sub-polar front occurred along 40N in the
northeastern JES; a separate front occurred in winter that was associated with the flow of warm water
restricted to the southern JES.
Small eddy energy was found in the cold water regime and large eddy energy in the warm water
regime. Satellite altimeter and drifter tracks were used to mark the Wonsan Eddy found in the Eastern
Korean Bay, a yearly late summer occurrence. Mechanical energy flux from the mean circulation to
mesoscale eddies occurred in EKWC, TC and the sub-polar front in the eastern JES with eddy kinetic
energy doubling time of 15–60 days. The yearly mean circulation east of the Korean coast is organized
into a broad, eddy-filled East Sea Current that contains weak anticyclonic gyres in the Ulleung and
Yamato Basins. It accelerates toward the Yamato Rise and against the eastern coast of the JES.
PUBLICATIONS
Lee, Dong-Kyu, Jae-Chul Lee, and Heung-Jae Lie, A Circulation study of the East Sea using satellitetracked drifters, Journal of the Korean Fisheries Society, 30, (6), Pusan, Korea, 1997.
Lee, Dong-Kyu, Pearn P. Niiler, Sang-Ryong Lee, Kuh Kim, Heung-Jai Lie, Energetics of the Surface
Circulation of the Japan/East Sea, J. Geophys. Res., 105(C8), 19,561-19573, 2000
Lee, Dong-Kyu, Pearn P. Niiler, Moon-Sik Suk, Comparison of Ocean Currents Observed from
Drifters and TP/ERS in the East Sea, Ocean and Polar Research, 23(2), 133-139, 2001.
Lee, Dong-Kyu, Pearn P. Niiler, Ocean Response to Typhoon Rusa in the South Sea of Korea
and in the East China Sea, J. Korean Soc. Oceanogr., 38, 2, 121-126.
Lee, Dong-Kyu, Pearn P. Niiler, The Energetic Surface Circulation Patterns of the Japan-East Sea, Deep
Sea Res. In printing.
Data
One day average drifter positions and currents at 15m. The format of data is:
Year Mon Day
1993
1993
9 9
9 10
DayCount*
2444
2445
Longitude Latitude
U (cm/s) V (cm/s)
121.711
121.901
28.69
16.08
23.667
24.040
58.40
37.68
*DayCount is the number of days since January 1, 1987.
Data can be downloaded from http://makaha.ucsd.edu/MyWeb/EASTSEA directory. Files for one day
average current are C-nnnnn where nnnnn indicates drifter id.
In addition to one day average current data, minimet data are also available. The format is:
Tear
1999
1999
Mon Day matlab day
7
7
Longitude
Latitude
11 730312.1516 132.482
11 730312.1935 132.487
41.245
41.245
U(cm/s) V(cm/s)
NaN
-3.98
NaN
-5.64
Wind Speed Wind Direction
6.71
6.91
-120.0
-125.2
Matlab days are date numbers calculated using matlab command datenum.
Wind directions are vector notaion, i.e. 0 degree wind is the wind blowing to the east. File names for
minimets are PosWind-nnnnn where nnnnn indicates drifter id.