講演情報
[AOS25-P02]High-resolution hydrographic surveys of the Kuroshio along 21.8°N
Ying-Chih Fang1、*Dai-Jyun Yu1、Huan-Jie Shao2、Bing-Rong Jiang2 (1.Department of Oceanography, College of Marine Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan、2.New Ocean Researcher 3 Marine Instrument Center, National Sun Yat-sen University, Kaohsiung, Taiwan)
キーワード：
SeaSoar、Towed-CTD、Kuroshio、Density front、Submesoscale variability、hydrographic survey
This task builds upon a starter project initiated in 2021 to reactivate a legacy SeaSoar system paired with a customized portable winch featuring approximately 500 m of wire. The SeaSoar is a robust towed undulating platform equipped with a standard SeaBird 911+ CTD package. Following the resolution of technical issues and successful sea trials, an operational procedure for deployment aboard research vessels has been established. Complementary data post-processing routines have been developed to separate measurements into discrete downcasts and upcasts, with corrections applied for sensor response time and thermal lag effects. The towed survey is designed to characterize thermohaline properties across the Kuroshio along 21.8°N south of Taiwan, spanning the South China Sea, Luzon Strait, and western Pacific Ocean. The portable winch's limited capacity restricts sampling to the upper ocean, above the deeper extent of the Kuroshio. The SeaSoar achieves cross-sectional observations of the upper ~150 m with 1-m vertical bins and ~2.5 km horizontal resolution. This poster presents preliminary results from three repeated transects conducted in 2025. The thermohaline field above ~50 m exhibits weak thermal stratification, while haline stratification becomes pronounced particularly in the western half of the transect, primarily due to relatively fresh South China Sea waters. At greater depths, a density front separates cold, fresh South China Sea waters from warmer, saltier waters associated with the Kuroshio. Corresponding isopycnals exhibit abrupt shoaling and deepening within 20 km, significantly smaller than the local baroclinic Rossby radius of ~70 km, suggesting that horizontal stratification and submesoscale dynamics influence Kuroshio variability. The observed isopycnal fluctuations may reflect locally generated internal tides or near-inertial waves. Future analysis of concurrent shipboard velocity data will help elucidate these dynamical processes.