Variations of Sea Surface flow fields in the East Asian marginal seas and the western North Pacific

Kaoru Ichikawa (Kyushu University, Japan)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Salient results from the 2017-2020 OSTST PIs

Presentation type: Type Forum only

This project covers comprehensive researches on variations in the western North Pacific and the East Asian marginal seas, so that various kinds of results are obtained. In this presentation, therefore, a few examples of our results on the Kuroshio, Oyashio and coastal regions are briefly introduced.
[Kuroshio ] The Kuroshio has taken a stable large meander path south of Japan for more than three years since 2017. From long-term monitoring using altimeters, the eastward volume transport of the Kuroshio is found significantly increased during this meandering period, while the net volume transport of the subtropical gyre remains unchanged, suggesting that a strengthened local gyre south of Japan is associated with the large meander of the Kuroshio. The meander is well represented in numerical assimilation models; assimilation of SSH field is crucial since skill of the model to forecast path variations strongly depends on the initial SSH field.
[Oyashio] Intensive in situ survey in the Oyashio region have revealed presence of a quasi-stationary jet from the Kuroshio Extension to the subarctic region, and its enhancement of the biological production in a deeper mixed layer caused by transport of warmer water and entrainment of surrounding nutrient-rich subarctic water.
[Coastal regions] In coastal areas around Japan, a new coastal retracker has been proposed that uses radargrams, or sequentially assembled adjacent waveforms. It successfully removes sigma0 blooms from calm water surface in isolated small bays, shrinking the data-absent distance (distance of the closest valid data point to the land) from 5 km to 3 km.
Kaoru Ichikawa
Kyushu University