STUDIES OF WATER TRANSPORT VARIABILITY USING SUBMARINECABLE VOLTAGE MEASUREMENTS IN THE SEA OF JAPANN. A. Palshin, L. L. Vanyan, R. D. Medzhitov, M. A. Evdoshenko
palshin@geo.sio.rssi.ru, vanyan@geo.sio.rssi.ru, medzhitov@access.orgland.ru
Shirshov Institute of Oceanology, Moscow, Russia

H. Utada
utada@eri.u-tokyo.ac.jp
Earthquake Research Institute, University of Tokyo, Japan

Abstract. Passive voltage measurements have been
carried out using the retired submarine JApan Sea Cable(JASC) for 5 years. Data collected in the long time periods
gave possibility to study long-term variability of
motionally induced voltage and its nature. JASC voltage isnearly proportional to integral water transport through theSea of Japan. Temporal variability of JASC voltage inshort-period synoptic (meso-scale) period range from 3 to
30 days was found to be most intensive, while long-period
synoptic and seasonal variability were found less intensive
though statistically significant. Comparison of JASC
voltage data with mean winds (wind stress curl) confirmedthat long-term variability of integral water transport isdirectly (locally and non-locally) wind-driven.

1 Introduction
Three owners installed JASC connecting Nakhodka(Russia) and Naoetsu (Japan) in 1969: Kokusai
Denshin Denwa, the Great Northern TelegraphCompany and ROSTELECOM. In 1995 a new fiberoptic telephone cable was installed and, due to thecourtesy of the owners, JASC was given to theJapanese and Russian scientists for jointexperiments. Earthquake Research Institute of theUniversity of Tokyo, Shirshov Institute ofOceanolgy and Pacific Oceanographic Institute (bothRussian Academy of Sciences) arranged aConsortium for the scientific use of JASC.
Geographical coordinates of the cable ends are42˚48'N and 132˚49'E (Nakhodka) and 37˚40.2'Nand 137˚58.8'E (near Naoetsu). The location of
JASC is shown at Fig. 1. On January 29 of 1996, ameasurement system was installed at the cablestation Nakhodka and monitoring of the natural
voltage was started. Acquisition system consists of adigital voltmeter, a laptop computer, a GPScontroller clock, and a 128 MB optical disk drive.
Sampling is made every second (Vanyan et al,1998). The measurements have been carried out for
5 years and are to be continued in the nearest years.
The data collected opens new opportunities forstudying long-term variability in the Sea of Japan.
The joint analysis of JASC voltage and mean winds
for the years 1996-1999 is considered in this paper.

Fig. 1. The location of JApan Sea Cable (JASC).

2 Separation of motionally induced signals
Cable voltage like any electromagnetic data obtainedin oceans and seas include both externally andmotionally induced signals. There is a period band
where both signals are significant (about 0.3 – 3days). Intensive solar-daily ionosphere and tidal
signals also belong to this band. Joint analysis of
JASC voltage and magnetic field from on-land
observatories (Kakioka, Vladivistok and others)
showed that squared coherence drops at periods ofseveral days thus confirming the dominance of
motionally induced electric field in the measured
signal at the long period band.
To separate motionally induced signal from raw
voltages daily mean values were calculated using
robust procedure (Hogg, 1979; Larsen et al., 1996).
Solar daily variations are efficiently suppressed bydaily averaging procedure while the tidal signals are
relatively week in the central part of the Japan Sea
and in JASC voltage. Comparison of daily meantime series with those obtained by the traditional
method, which uses transfer function calculation,
confirmed that our simplified procedure gives
reasonable results at periods greater than 3 days.

increased in the second half of the year for all years
in question.

Fig. 2. Monthly mean (lower panel) JASC voltage and its
standard deviation (upper panel) for 1997-1999.

Previous theoretical studies (Palshin et al., 1997)
confirmed that JASC voltage is nearly proportional
to integral water transport through the Sea of Japan.
For further studies we expressed daily and monthly
mean JASC voltage in water transport units using
the obtained scaling factor. Monthly mean values
and its deviation within month intervals are shown atFig. 2. It is worth mentioning that for the purposesof studies of temporal variability the exact
knowledge of the scaling factor is not necessary.
Practically it is enough to know that relationshipbetween the voltage and water transport is close
linear.

3 Seasonal and synoptic variability
Statistical analysis of daily mean cable voltage(expressed in water transport units) for three years(1997 - 1999) was carried out using the following
assumption of time series structure, which isconventional in hydro-meteorological studies (see e.
g. Gulev et al., 1994):
x(t)=F(t)+S(t)+E(t),where F(t) is inter-annual trend, S(t) is regularharmonic seasonal variability and E(t) is residualfluctuations (synoptic variability).
Residual time series E(t) was divided into two
ranges from 30 to 100 days EL(t) ("long-period")
and from 3 to 30 days ES(t) ("short-period").
Short-period variability ES(t) was found to be themost significant: it is responsible for 60-70% of total
deviation. In 1997 and 1998 we found the increaseof the intensity of short-period variability ES(t) inAugust-October (typhoon season in the Sea ofJapan). The intensity of long-period variability EL(t)Fig. 3. Seasonal and synoptic variability of integral watertransport derived from JASC voltage. A – seasonal (twofirst harmonics) variability, B – long-period synoptic
variability, C – short-period synoptic variability.

Seasonal variability is characterized bydominance of the second (half-year) harmonic, while
the first harmonic is also statistically significant. in
Autumn (September-October) and two maxima in
Winter (January) and in Summer (June-July).
The most exiting fact is the increase ofvariability in all ranges (seasonal and synoptic) in
the year 1999, while the parameters of the variability
in two previous years are very close. Fig. 3 shows
seasonal and synoptic variability for three years
1997-1999.

4 Integral water transport versus mean
winds
There is experimental and theoretical evidence
that barotropic flows in the oceans are directly winddriven. This process is usually explained as thetransmission of vorticity from the wind to the ocean
through Ekman pumping (see Chave et al., 1992;
Fujii and Chave, 1999).
Daily mean JASC voltage is rather accurate
measure of integral water transport through thecentral part of the Japan Sea, because main currents
pass from the East China Sea through the Sea ofJapan to the Pacific Ocean (see Fig. 4).

Fig. 4. Surface currents in the Sea of Japan (after Uda,
1935 and Yurasov and Yarichin, 1991). Shaded rectangle
shows the region where spatial averaging of SeaWIFS
meteorological data were carried out. Position of JASC isshown as thick black line with circles at the ends. Letters
indicate the regions (4° x 4°) where CERSAT mean winds
were analyzed (see text).

SeaWIFS meteorological data (wind speed andair pressure) with 4-hour sampling rate andCERSAT mean winds (weekly and monthly windstress, wind divergence and wind stress curl) with 1°
spatial resolution were used. SeaWIFS data werespatially averaged within shaded rectangle at Fig. 4
and spatial gradients of air pressure were calculated
additionally. CERSAT data were analyzed in 4
regions (see Fig. 4) selected in the central part of the
Sea of Japan (A and B), in the Pacific Ocean to thesouth-east off Japan (C) and in the Korean Strait(D). All the data were processed in the same manneras JASC voltage.
The comparison of time series gives thefollowing results:- short-period synoptic variability of integral
water transport is driven by spatially averaged local
zonal winds or meridional pressure gradient. Most of
the time there is a direct proportionality (see Fig. 5),
but there are also time intervals when proportionality
is inverse. At Fig. 5C the time interval of directproportionality is shown, but at end of this interval
the proportionality evidently changes to inverse one.
- long-period synoptic variability of integral
water transport is driven by a remote wind stress curl
and a zonal wind stress in the Korean Strait (see Fig.
6).

Fig. 5. Short-period synoptic variability of the integral
water transport derived from JASC voltage Q (solid line)
versus spatially averaged local zonal wind speed U(dashed line). Time intervals with the inverse
proportionality are shown

Fig. 6. Long-period synoptic variability of the integral
water transport derived from JASC voltage Q (solid line)
versus curl of wind stress τ in the Korean Strait (dashedline) for 1997-1999.

The correlation between the water transport andwind curl stress is inverse. The behavior of long–term synoptic variability is evidently different fromyear to year.
However, any significant correlation with themeridional wind speed (and zonal pressure gradient)in short period range has not been found. There isalso no linkage between integral water transport andmeteorological parameters under study in a long
period band except Korean Strait region. Most
probably, the remote wind stress curl in the Soyaand Tsugaru Straits also effects the processes underconsideration.

5 Discussion and perspectives for future
The sources of short-period and long-period
synoptic variability of integral water mass transport
are different: short-period variability (3-30 days) isdriven by local zonal winds, while long-periodvariability (30-100 days) is driven by the remotewind stress curl. The parameter of both seasonal andsynoptic variability changed in the year 1999.
The mechanism of local forcing is most probably
connected with the passage of active atmospheric
cyclones over the Sea of Japan. Thus, a goodcorrelation between JASC voltage and zonal wind
was found in the middle of September 1997, when
typhoon “Oliwa” passed across the southern part of
the Sea of Japan (see Fig. 7).

The remote forcing could be explained asfollows: wind stress curl in the Korean Strait acts as
a valve controls the input of water masses in the Seaof Japan and hence controlling the integral watertransport through the Sea of Japan. The sameprocesses are expected in the Tsugaru and La
Perouse (Soya) Straits and the corresponding
analysis will be carried out in the nearest future.
The processes controlling the seasonal variabilityof integral water transport are not understood yet.
The existence of minima in August-September
confirmed by the results obtained with PusanHamada voltage measurements and ADCP data [Lyuand Kim, 2001]. That is another problem to besolved.
The noticeable difference of the variability
character of in 1997-1998 and that of the year 1999
is probably related to the ocean-scale processes
caused by the El Niсo phenomenon.
The following lines of investigations are ofparticular interest in future:- to continue the acquisition of submarine cable
voltage data in the Sea of Japan and to study thecorrelation between the voltage time series obtainedby different cables and reference conventional
oceanographic measurements (current meters,ADCP, STD etc.). This allows calibrating thevoltages properly.
- to continue the joint analysis of submarine
cable voltages (using all the cables available in theSea of Japan), meteorological parameters (airpressure and winds), and remote sensing data (SSHand SST data). The main objective of the analysis is
not only to establish the relationships between
different processes but also to understand themechanisms of ocean-atmosphere interaction in theSea of Japan.

6 Conclusions

Fig. 7. Comparison of JASC voltage (solid line) with azonal wind speed (dashed line) during the passage oftyphoon “Oliwa” over the southern part of the Sea ofJapan (lower panel). NOAA image of typhoon “Oliwa” on
September 15, 1997 (upper panel).

Comparative analysis of the integral watertransport variability derived from JASC voltage,
demonstrated that the most intensive short period
component is driven by the variability of the zonal
wind speed (stress) at the central part of the Japan
Sea (local forcing), while long period variability iscontrolled by the variability of a wind stress curl at
the Korean (Tsushima) Strait (remote forcing). The
essential changes of the correlation parameters fromseason to season and from year to year were also
distinguished. The results obtained gave a possibility
to judge upon the nature of the observed correlationof variability of the integral water transport andmeteorological conditions.
The results obtained confirmed that JASC
voltage measurements provide an effective tool forstudying long-term basin-scale seasonal andsynoptic processes in the Japan Sea and could
provide important constrains of circulation models
under development.
The importance of cable voltage results could
increase when a joint analysis of all data obtained by
all submarine cable available in the Sea of Japan will
be made. Cable voltage measurements associatedwith conventional oceanographic data could giveinformation on integral water mass and heattransport throughAcknowledgement. The Russian Foundation for Basic
Researches (Grant 98-05-64654) and the Ministry of
Education, Science, Sports and Culture of Japan (Grant06041025) and the Ocean Hemisphere Network Project
support this research.

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