Characteristics of Semi-diurnal and Diurnal Currents at a KOGA Station over the East China Sea Shelf

• Journal title : Ocean and Polar Research
• Volume 36, Issue 1,  2014, pp.59-69
• Publisher : Korea Institute of Ocean Science & Technology
• DOI : 10.4217/OPR.2014.36.1.059
Title & Authors
Characteristics of Semi-diurnal and Diurnal Currents at a KOGA Station over the East China Sea Shelf
Noh, Su-Yun; Seung, Young Ho; Lim, Eun-Pyo; You, Hak-Yeol;

Abstract
The long-term mooring performed at a KOGA station, located at about $\small{30^{\circ}20^{\prime}N}$, $\small{126^{\circ}12^{\prime}E}$ in the East China Sea shelf, shows some different behaviors between "semi-diurnal" and "diurnal currents" defined as the currents with periods around, respectively, a half day and a day. They appear to be predominantly tidal having significant coherences with sea level changes around the semi-diurnal and diurnal frequencies. The "semi-diurnal current" is strongly barotropic all year round. However, contrastingly, it is largely baroclinic in summer in the area about 70 km nearer to the continental slope, referred to as the "slope-area", as was found in previous current observations. The "diurnal current" of tidal origin is strongly barotropic in winter. In spring and summer, however, it becomes more baroclinic although it still remains largely barotropic, also showing more of its barotropic nature than in the "slope-area". The inertial oscillation contributing to the "diurnal current" appears to be more prominent when the current is baroclinic, indicating the important role played by stratification in generation of inertial oscillations. Downward energy propagation of inertial oscillation is not observed, suggesting that it is not created at the surface by wind. Considering that the study area is both near a critical latitude and proximity to the continental slope, it is suggested that parametric subharmonic instability (PSI) plays a significant role in creating the baroclinic inertial oscillation.
Keywords
semi-diurnal current;diurnal current;East China Sea;KOGA;
Language
English
Cited by
References
1.
Baines PG (1982) On internal tide generation models. Deep-Sea Res 29(3):307-338

2.
Choi BH (1980) A tidal model of the Yellow Sea and the Eastern China Sea. KORDI, Ansan, 72 p

3.
Emery WJ, Thomson RE (1997) Data analysis methods in physical oceanography. Elsevier, Amsterdam, 638 p

4.
Ichikawa H, Beardsley R (2002) The Current System in the Yellow and East China Seas. J Oceanogr 58(1):77-92

5.
Isobe A (2008) Recent advances in ocean-circulation research on the Yellow Sea and East China Sea shelves. J Oceanogr 64(4):569-584

6.
KHOA (2012) Reports of the project, Analyses of data obtained from Korea Ocean Observing Network (KOON). 271 p (in Korean)

7.
KHOA (2013) IEODO Ocean Research Station http:// ieodo.khoa.go.kr Accesed 4 Mar 2014

8.
Kuroda Y, Mitsudera H (1995) Observation of internal tides in the East China Sea with an underwater sliding vehicle. J Geophys Res-Oceans 100(C6):10801-10816

9.
Larsen LH, Cannon GA, Choi BH (1985) East China Sea tide currents. Cont Shelf Res 4(1-2):77-103

10.
Lie HJ, Cho CH (1994) On the origin of the Tsushima Warm Current. J Geophys Res-Oceans 99(C12):25081-25091

11.
Lie HJ, Cho CH, Lee JH, Lee S, Tang Y, Zou E (2001) Does the Yellow Sea Warm Current really exist as a persistent mean flow? J Geophys Res-Oceans 106(C10): 22199-22210

12.
MacKinnon JA, Alford MH, Sun O, Pinkel R, Zhao Z, Klymak J (2013) Parametric Subharmonic Instability of the Internal Tide at $29^{\circ}N$. J Phys Oceanogr 43(1):17-28

13.
Niwa Y, Hibiya T (2004) Three-dimensional numerical simulation of M2 internal tides in the East China Sea. J Geophys Res-Oceans 109(C4):C04027

14.
Park JH, Lie HJ, Guo B (2011) Observation of Semi-diurnal Internal Tides and Near-inertial Waves at the Shelf Break of the East China Sea. Ocean and Polar Res 33(4):409-419

15.
Pawlowicz R, Beardsley B, Lentz S (2002) Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE. Comput Geosci 28(8):929-937

16.
Su J (1998) Circulation dynamics of the China Seas north of $18^{\circ}N$. J Korean Soc Oceanogr 11:483-505

17.
Takahashi D, Morimoto A (2013) Mean field and annual variation of surface flow in the East China Sea as revealed by combining satellite altimeter and drifter data. Prog Oceanogr 111:125-139

18.
Torrence C, Compo GP (1998) A Practical Guide to Wavelet Analysis. B Am Meteorol Soc 79(1):61-78

19.
Yanagi T, Morimoto A, Ichikawa K (1997) Co-tidal and corange charts for the East China Sea and the Yellow Sea derived from satellite altimetric data. J Oceanogr 53(3): 303-310