TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 60 (No. 2), pp. 425-437, 2004

Characteristics of SSH Anomaly Based on TOPEX/POSEIDON Altimetry and in situ Measured Velocity and Transport of Oyashio on OICE

Shin-ichi Ito1*, Kazuyuki Uehara2, Takashi Miyao3, Hideo Miyake4, Ichiro Yasuda5, Tomowo Watanabe6 and Yugo Shimizu1

1Tohoku National Fisheries Institute, Shinhama-cho, Shiogama, Miyagi 985-0001, Japan
2National Research Institute for Far Seas Fisheries, Orito, Shimizu, Shizuoka 424-8633, Japan
3Hakodate Marine Observatory, Mihara, Hakodate, Hokkaido 041-0806, Japan
4Hokkaido University, Minato-cho, Hakodate, Hokkaido 041-8611, Japan
5Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
6National Research Institute of Fisheries Science, Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236-8648, Japan

(Received 3 January 2003; in revised form 9 October 2003; accepted 10 October 2003)

Abstract: An observation line along the TOPEX/POSEIDON (T/P) ground track 060 was set to estimate the Oyashio transport. We call this line the OICE (Oyashio Intensive observation line off-Cape Erimo) along which we have been conducting repeated hydrographic observations and maintaining mooring systems. T/P derived sea surface height anomaly (SSHA) was compared with velocity and transport on OICE. Although the decorrelation scale of SSHA was estimated at about 80-110 km in the Oyashio region, the SSHA also contains horizontal, small-scale noise, which was eliminated using a Gaussian filter. In the comparison between the SSHA difference across two selected points and the subsurface velocity measured by a moored Acoustic Doppler Current Profiler (ADCP), the highest correlation (0.92) appeared when the smoothing scale was set at 30 km with the two points as near as possible. For the transport in the Oyashio region, the geostrophic transport between 39°30´ N and 42°N was compared with the SSHA difference across the same two points. In this case the highest correlations (0.79, 0.88 and 0.93) occurred when the smoothing scale was set at 38, 6 and 9 km for reference levels of 1000, 2000 and 3000 db, respectively. The annual mean transport was estimated as 9.46 Sv in the 3000 db reference case. The Oyashio transport time series was derived from the T/P SSHA data, and the transports are smaller than that estimated from the Sverdrup balance in 1994-1996 and larger than that in 1997-2000. This difference is consistent with baroclinic response to wind stress field.

*Corresponding author E-mail: goito@affrc.go.jp

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