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第302回 大気海洋物理学・気候力学セミナー のおしらせ

日　時： 10月19日(木) 9:30-12:00
Date ： Thu., 19 Oct. 9:30-12:00
場　所： 低温研三階講堂
Place ： ILTS Bldg. 3F auditorium

Speaker:Mensah Vigan Joel Sebastien(ILTS/PD)
Title：Evolution of the water masses associated with the Kuroshio from the Luzon Strait to the East of Taiwan

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Evolution of the water masses associated with the Kuroshio from the Luzon Strait to the East of Taiwan 
（Mensah Vigan Joel Sebastien）発表要旨:


The temporal and spatial variability of the water masses found along the 
Kuroshio between the Luzon Strait and the east of Taiwan is studied at 
two levels: the tropical waters (TW), whose core lies at ~150m and is 
marked by a salinity maximum (Smax) and the intermediate waters (IW), 
with a core around ~600 m presenting a salinity minimum (Smin). To study 
the evolution of the Kuroshio Tropical Water (KTW), historical 
conductivity temperature depth (CTD) profiles are analyzed based on root 
mean square (rms) difference of the salinity along isopycnals. This 
analysis enables water masses in the Kuroshio and the vicinity, as well 
as their interactions, to be tracked and distinguished. Vertical and 
horizontal eddy diffusivities are then calculated from hydrographic and 
current velocity data to elucidate the dynamics underlying the KTW 
interactions with the surrounding water masses. KTW permanently flows 
with the Kuroshio and is modified under the effect of strong vertical 
diffusivity O(10-3 m2 s-1) in the Luzon Strait. Further north its 
averaged properties are conserved by the compensating effects of 
vertical mixing and advection of saltier water from the east. 
The variability of the IW east of Luzon and Taiwan is investigated using 
2 years of data acquired from moored instrumented lines and shipboard 
hydrographic and current velocity surveys. An empirical formula is 
deduced to estimate the IW salinity minimum east of Taiwan using 
temperature measurements around 580 m depth. The properties of the IW 
east of Taiwan vary greatly as a result of variable contributions from 
three water masses including the high salinity South China Sea 
Intermediate Water (SCSIW), the low salinity minimum North Pacific 
Intermediate Water (NPIW), and the mid-range Kuroshio Intermediate Water 
(KIW). Our analysis concludes that the northward transport of KIW from 
east of Luzon to east of Taiwan is not a steady process. KIW reaches the 
east of Taiwan only when Kuroshio intensity and layer thickness is large.
 As a result, over a period of 2 years, the fresher North Pacific IW 
(NPIW) is found east of Taiwan ~55% of the time. 

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