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Preliminary Results from a 1000-km Scale Three-Dimensional Tomography Experiment in the Kuroshio Extension Region

 

Gang Yuan1, Iwao Nakano2, Hidetoshi Fujimori2, Toshiaki Nakamura2, Takashi Kamoshida3, and Akio Kaya3

 

1.IPRC/SOEST, University of Hawaii,

1000 Pope Road, Marine Science Bldg. Room 220, Honolulu, HI 96822, USA

2.Japan Marine Science and Technology Center,

2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

3.Oki Electric Industry Co., Lid., 4-10-3 Shibaura, Minato-ku, Tokyo 108, Japan

 

A 1000-km scale three-dimensional acoustic tomography experiment has been conducted in the Kuroshio Extension region during July to September 1997. Inversions of the acoustic travel time data provide estimates of the time evolution of the three-dimensional temperature field over a 1000-km x 1000-km region. The three-dimensional temperature field dynamically shows the variable meander of the Kuroshio Extension with high time resolution. An energetic mesoscale cold eddy with spatial scales of 100-200 km is resolved. During the observation period, the Kuroshio Extension front takes an extreme meander path and induces a pair of warm and cold eddies at the end of Summer 1997. These results are consistent with those of other measurements such as XCTD, ADCP and TOPEX/POSEIDON satellite altimetry. Variable oceanic structures in a 1000-km domain, which are difficult targets for conventional point measurement techniques, can be measured well by ocean acoustic tomography with real-time data telemetry.

 

Introduction

 

After separating from the east coast of Japan at (35。?, 142。?), warm high salinity Kuroshio water meets cold low salinity southward flowing Oyashio water, and turns eastward forming the Kuroshio-Oyashio frontal zone (the Kuroshio Extension) in the region 30-40。?, 140-180。? (Figure 1) [Kawai,1972]. The Kuroshio Extension is characterized as an eastward flowing inertial jet accompanied by large amplitude meanders and vigorous pinched-off eddies or rings. There have been many previous studies by Schmitz (1987 and 1988), Oiu (1992 and 1995), Mitchell et al. (1996), and Wang and Koblinsky (1996), about the variability and dynamics in the Kuroshio Extension region; most of these studies were based on direct current measurements across the Kuroshio Extension along 152。?, 165。? and 175。?, and on satellite remote sensing (altimetry and infrared imagery); because of the difficulty of direct, in situ observations of the large-scale four-dimensional structure of the Kuroshio Extension, numerical modeling has also been used Hurlburt et al. (1996). The temporal and spatial variations of the deep interior of the ocean still remain to be measured using new methods.

 

 

 

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