Monitoring currents and waves in the Asian marginal seas and the western North Pacific with complementary observations and models

Author:

Kaoru Ichikawa - (RIAM)

Co-Investigator(s):

Hiroaki Asai (JMA)
Naoto Ebuchi (ILTS)
Yosuke Fujii (MRI)
Naoki Hirose (RIAM)
Osamu Isoguchi (RSTCJ)
Shin-Ichi Ito (AORI)
Nadao Kohno (MRI)
Hiroshi Kuroda (AFFRC)
Hitoshi Tamura (PARI)
Hiroshi Uchida (JAMSTEC)
Taku Wagawa (JFREA)

Abstract:

This proposal to participate in the Ocean Surface Topography Science Team (OST-ST) is an extension of the present OST-ST project entitled as ""Variations of sea surface flow fields in the East Asian marginal seas and western North Pacific"" (PI: Kaoru Ichikawa). Using satellite altimeters, 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. Moreover, we have extended our description to 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.

Therefore, the primary aim of this proposal is to keep extending our understanding of the surface flow fields in the western North Pacific and surrounding Asian marginal seas. We will keep investigations on variations of the Kuroshio and Oyashio currents in the western North Pacific by combining altimetry data with in situ observations and numerical models: These currents play important roles in oceanic heat transports and also significantly affects biological activities and formation of fishing grounds.

Meanwhile, regional impacts on biological activities and formation of fishing grounds could be more significant for variations of the Tsushima Warm Current System (i.e., the Taiwan warm current, the Tsushima warm current and Tsugaru and Soya currents) in the marginal seas around Japan (the East China Sea, the Japan Sea and the Sea of Okhotsk). Since the performance of satellite altimeters is generally limited in those coastal areas and marginal seas where temporal and spatial scales of phenomena are small, we have settled various complementary observations by the High-Frequency (HF) ocean radar systems, Acoustic Doppler Current Profiler (ADCP) and Global Navigation Satellite System (GNSS) mounted on ferries crossing the straits, and repeated salinity and temperature measurements by an underwater glider, in order to monitor variations of the Tsushima Warm Current System. In addition, we develop a waveform retracking algorithm for conventional altimeters to handle contaminated waveforms in coastal areas to provide more accurate observations of sea surface height (SSH) and significant wave height (SWH) even in coastal areas and marginal seas.

In parallel, we will explore operational data assimilation systems for forecasting current and wave fields. Various knowledge accumulated by intensive in situ observations in this proposal will Eventually evaluate the developing operational systems in future.

In this proposal, we shall continue in situ observations. They include hydrographic and mooring field observations, HF radars, surface drifters, underwater gliders and bottom pressure gauges. They will be used for basic oceanographic studies and may be eventually used as calibration/validation data for Jason-3/CS and Sentinel-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. We intend to obtain new understandings of circulations in the western North Pacific and the Asian marginal seas through those aspiring studies.