Observation of Topographic Rossby Waves Triggered by Kuroshio Path Meander in the East China Sea. Issue 8 (24th August 2022)

• Record Type: Journal Article
• Authors: Chen, Juntian; Zhu, Xiao‐Hua; Zheng, Hua; Nakamura, Hirohiko; Zhao, Ruixiang; Wang, Min; Park, Jae‐Hun; Nishina, Ayako
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-24
• Subjects: topographic Rossby waves -- east China sea -- Kuroshio -- path meander -- ray tracing; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2022JC018667
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Topographic Rossby waves (TRWs) are motions triggered by potential vorticity adjustments, which strongly contribute to deep ocean variabilities. This study discerned near‐36‐day significant along‐slope fluctuations, speculated to be TRWs, using deep current observations over the continental slope in the East China Sea (ECS). The TRWs propagated southwestward along the continental slope with wavelengths of ∼95 km in the northern stations and ∼36 km in the southern stations where the slope is steeper. The group velocity was estimated to be ∼15.5 km/day, and the maximum current speed was ∼10 cm/s. It was assumed that the energy source originates from the Kuroshio path meander, which has a similar typical period to the TRWs and can induce surface eddy kinetic energy, along with depth variations of water column in west of the Tokara Strait. Analyses involving ray tracing model of TRWs showed consistency with the observations in wave characteristics, thereby confirming our postulation regarding the TRWs and their origin. Moreover, the energy rays, emanated from the origin, intensively propagated along the slope; and after climbing over the successive slope, eventually stopped when reaching the flat areas. Additionally, the TRWs' hyperbolic intensification and vertical coherent phase features were revealed in model results. The seasonality of the Kuroshio path meander induced depth variation of water column was estimated to be prevalent in February and August. Overall, this study revealed the propagation features and generation mechanism of TRWs over the continental slope in the ECS for the first time. Plain Language Summary: Energy transfer and cascades are vital for ocean dynamic balance, while topographic Rossby waves (TRWs) may have a similar function in the deep ocean. However, the current scientific understanding regarding TRWs in the East China Sea (ECS) remains limited. Significant near‐36‐day TRWs, with a group velocity of ∼15.5 km/day, beneath the Kuroshio over the continental slope in the ECS were identified through deep current observations. The ray tracing model further revealed that the energy of TRWs originates from the Kuroshio path meander and propagates uphill southwestward. This study is the first, to our knowledge, to establish the relationship between the Kuroshio and TRWs. Collectively, these results provide insights about the influence of the Kuroshio in deep ocean dynamics. Key Points: Near‐36‐day topographic Rossby waves were firstly observed along the continental slope in the East China Sea The energy source was identified as the frequent Kuroshio path meander with consistent periods in west of the Tokara Strait The relationship between the topographic Rossby waves and the Kuroshio path meander advance understanding of local multi‐scale dynamics