Variations of sea surface flow fields in the East Asian marginal seas and the western North Pacific

Author:

Kaoru Ichikawa - (Research Institute for Applied Mechanics, Kyushu University)

Co-Investigator(s):

Naoto EBUCHI (Institute of Low Temperature Science, Hokkaido University)
Yosuke FUJII (Meteorological Research Institute, Japan Meteorological Agency)
Yoichi FUKUDA (Graduate School of Science, Kyoto University)
Naoki HIROSE (Research Institute for Applied Mechanics, Kyushu University)
Osamu ISOGUCHI (Remote Sensing Technology Center of Japan)
Shinichi ITO (Atmosphere and Ocean Research Institute, The University of Tokyo)
Hiroshi KURODA (Hokkaido Nat. Fish. Res. Inst., Japan Fisheries Research and Education Agency)
Akihiko MORIMOTO (Center for Marine Environmental Studies, Ehime University)
Yoshiaki TAMURA (Mizusawa VLBI Observatory, National Astronomical Observatory)
Hiroshi UCHIDA (Japan Agency for Marine-Earth Science and Technology)

Abstract:

Variations of sea surface flow fields in the East Asian marginal seas and the western North Pacific — Locations of the Tsushima Warm Current System; namely, the **Taiwan Warm Current** (from the South China Sea to the East China Sea through the Taiwan Strait), the **Tsushima Warm Current** (through the Tsushima Strait to the Japan Sea), the **Tsugaru Current** (through the Tsugaru Strait to the Pacific Ocean), and the **Soya Current** (through the Soya Strait to the Sea of Okhotsk). Schematic lines for the **Kuroshio**, the **Oyashio**, and the **East Sakhalin Current** are also plotted in the panel. Several Jason subsatellite tracks are indicated, including the OICE and ASUKA observation lines.

This proposal to participate in the Ocean Science Topography Science Team (OST-ST) is an extension of the current OST-ST project entitled as "Variations of sea surface height and flow fields in the western North Pacifica and surrounding marginal seas" (PI: Kaoru Ichikawa). We have achieved many descriptive physical oceanographic results on variations of flow fields in the western North Pacific, including the Kuroshio, Kuroshio Extension and Oyashio current systems and associated variations in geodetic fields. Moreover, we have extended our description to the currents in marginal seas as the East China Sea, the Japan Sea and the Sea of Okhotsk. Furthermore, progress of the ocean data assimilation techniques has been achieved to the stage being able to accumulate these observations of large-scale current systems, meso-scale eddies and regional currents in the marginal seas.

The primary aim of this proposal is to extend our understanding of the surface flow fields in the western North Pacific and surrounding marginal seas. For currents in marginal seas around Japan (the East China Sea, the Japan Sea and the Sea of Okhotsk), the straits connecting to those marginal seas (i.e. the Taiwan Strait, the Tsushima Striat, the Tsugaru Strait and the Soya Strait) are most essential areas. Since the altimeters cannot properly work in those areas where the depth is shallow and lands are close, we have settled the High-Frequency (HF) ocean radar systems and Acoustic Doppler Current Profiler (ADCP) mounted on ferries crossing the straits to monitor variations of currents in each strait. We will accumulate these independent observations by data assimilation systems together with the altimetry data, to provide self-consistent observations. At the same time, we will conduct development of regional tidal models, modification of the altimeters retrieving algorithm, and the sea surface height measurements by Global Navigation Satellite System (GNSS) to assist satellite altimeters in coastal zones. Furthermore, we will also relate variations of those currents in the marginal seas to variations of the Kuroshio and Oyashio current systems in the western North Pacific, which will be investigated in parallel by combining altimetry data with in situ observations and numerical models.

In this proposal, we shall continue in situ observations. They include hydrographic and mooring field observations, HF radars, surface drifters, and bottom pressure gauges. They will be used for basic oceanographic studies, and may be eventually used as calibration/validation data for Jason-2/Jason-3 by any other OST-ST groups. Similarly, we shall maintain operational products of ocean monitoring and forecasting systems produced by Japan Meteorological Agency (JMA). Meanwhile, assimilated results from comprehensive models will be used for basic studies. In addition, gravity changes due to huge oceanic motions such as a large Kuroshio meander will be examined by use of a dense network of accurate gravity field measurements in Japan. We intend to obtain new understandings of circulations in the western North Pacific through those aspiring studies.