Variability of topographic Rossby waves observed on the shelfbreak of the Chukchi Sea

Ahyoung Ku, Inha University, Department of Ocean Sciences, Incheon, South Korea, Jae-Hun Park, Inha University, Ocean Sciences, Incheon, South Korea, Young Ho Seung, Inha Univ, Incheon, Korea, Republic of (South), Chanhyung Jeon, Pusan National University, Department of Oceanography, Busan, South Korea, Youngseok Choi, Inha University, Department of Marine science and Biologycal Engeneering, Incheon, Korea, Republic of (South), Koji Shimada, Tokyo University of Mar. S&T, Tokyo, Japan, Kyoung-Ho Cho, KIOST, Ansan/Gyeonggi, Korea, Republic of (South) and Eri Yoshizawa, Japan Aerospace Exploration Agency, Tsukuba, Japan
One-year-long current measurements from August 2014 at 193 m in the Chukchi Sea shelfbreak (74.80°N, 167.89°W) showed subinertial topographic Rossby waves (TRWs) around 35-hour period. The mooring was equipped with an upward-looking acoustic Doppler current profiler (ADCP, RDI WHS 600 kHz) at 58 m and a downward-looking ADCP (RDI WHS 300 kHz) at 63 m, 29 temperature sensors, and four salinity sensors. The observations reveal a feature of TRWs such as bottom-intensified up-slope current fluctuations significantly coherent with near-bottom temperature fluctuations with a phase lag of approximately 90° at 35 h. Theoretical estimates of wavelength, angle of wavenumber vector, and bottom-trapping depth confirm that the observed near 35-h TRWs are plausible in the study area. Energetic TRWs are observed in September and October, during the sea-ice free season, while weak TRWs in other sea-ice covered months. Overall, TRW events coincide with strong wind-stress events around the study area, suggesting that the TRWs are triggered by atmospheric forcings. These findings imply that increasing sea-ice loss can result in the generation of more energetic TRWs, which could play an important role in water exchange between the shallow continental shelf and deep ocean.