Enhanced Diapycnal Mixing due to Near-Inertial Internal Waves Propagating through an Anticyclonic Eddy in the Ice-Free Chukchi Plateau YUSUKE KAWAGUCHI a AND SHIGETO NISHINO Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan JUN INOUE National Institute of Polar Research, Tokyo, and Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan KATSUHISA MAENO b Global Ocean Development Inc., Yokohama, and Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan HIROKI TAKEDA Tokyo Gakugei University, Tokyo, and Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan KAZUHIRO OSHIMA Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan (Manuscript received 10 August 2015, in final form 5 May 2016) ABSTRACT The Arctic Ocean is known to be quiescent in terms of turbulent kinetic energy (TKE) associated with internal waves. To investigate the current state of TKE in the seasonally ice-free Chukchi Plateau, Arctic Ocean, this study performed a 3-week, fixed-point observation (FPO) using repeated microstructure, hydrographic, and current measurements in September 2014. During the FPO program, the microstructure observation detected noticeable peaks of TKE dissipation rate « during the transect of an anticyclonic eddy moving across the FPO station. Particularly, « had a significant elevation in the lower halocline layer, near the critical level, reaching the order of 10 28 W kg 21 . The ADCP-measured current displayed energetic near-inertial internal waves (NIWs) propagating via the stratification at the top and bottom of the anticyclone. According to spectral analyses of horizontal velocity, the waves had almost downward energy propagation, and its current amplitude reached ;10 cm s 21 . The WKB scaling, incorporating vertical variations of relative vorticity, suggests that increased wave energy near the two pycnoclines was associated with diminishing group velocity at the corresponding depths. The finescale parame- terization using observed near-inertial velocity and buoyancy frequency successfully reproduced the characteristics of observed «, supporting that the near-inertial kinetic energy can be effectively dissipated into turbulence near the critical layer. According to a mixed layer slab model, a rapidly moving storm that has passed over in the first week likely delivered the bulk of NIW kinetic energy, eventually captured by the vortex, into the surface water. a Current affiliation: Institute of Arctic Climate and Environment Research, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan. b Current affiliation: Nippon Marine Enterprises, Ltd., Yokosuka, Japan. Corresponding author address: Yusuke Kawaguchi, Institute of Arctic Climate and Environment Research, Japan Agency for Marine- Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa Prefecture 237-0061, Japan. E-mail: yusuke.kawaguchi@jamstec.go.jp Denotes Open Access content. AUGUST 2016 KAWAGUCHI ET AL. 2457 DOI: 10.1175/JPO-D-15-0150.1 Ó 2016 American Meteorological Society Unauthenticated | Downloaded 06/16/22 10:57 PM UTC