Wind-Induced Topographic Rossby Waves in the Southwestern Slope of the Chukchi Abyssal Plain

Abstract

Near-bottom currents collected over 1 year (August 2021-22) using a current- and pressure-recording inverted echo sounder (CPIES) at a depth of 1060 m showed fluctuations within a frequency band between 2 and 6.5 days near the southwestern slope of the Chukchi Abyssal Plain. The amplitude of the fluctuations was approximately 8 cm s21 on average during the summer months and weakened to approximately 3 cm s21 between February and June 2022. Similar fluctuations were reproduced by the data-assimilated Hybrid Coordinate Ocean Model (HYCOM), confirming that they were bottom intensified. Calculations of the bottom-trapping scale using HYCOM revealed that these fluctuations could be attributed to topographic Rossby waves (TRWs) with a length scale of approximately 50 km. The spatial distributions of TRWs in HYCOM and ray-tracing results suggest that TRWs likely propagated from the west-southwest. It is suggested that these TRWs were triggered by nonlocal wind stress curl (WSC), 220 km to the west along the continental slope, as the coherence in the TRW frequency band between the TRWs and WSC was significant. The weaker TRW signal from February to June 2022 was related to weaker WSC and higher sea ice concentration in the study area. The stronger TRWs from July to October occurred when the WSC was stronger and the sea ice concentration was lower in the study area. Our findings imply that changes in the Arctic WSC field or a longer sea ice-free season could trigger more energetic and frequent TRWs, observable down to 1000-m depth around the southwestern slope of the Chukchi Abyssal Plain.