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海氷-海洋境界層における乱流混合と熱塩バランスについて
川口, 悠介
Permalink : http://hdl.handle.net/2115/91846
JaLCDOI : 10.14943/lowtemsci.82.57
KEYWORDS : 海氷-海洋境界層;乱流混合;エクマン螺旋;浮力フラックス;北極海;Ice-ocean boundary layer;turbulent mixing;Ekman spiral;buoyancy flux;Arctic Ocean
Abstract
本研究は，海氷-海洋境界層における乱流による熱塩輸送と海氷の成長・融解について，北極海中央海盆域で現地調査を実施した．この観測では，海氷とともに砕氷船を漂流させながら海氷直下の観測を継続的に行い，海氷運動による境界層内の水温，塩分の時空間構造，および，乱流混合に関する知見を得た．多層式流向流速計を用いた調査では，水平流速が深さとともに時計回りに回転するエクマン螺旋の構造を捉えた．乱流エネルギー（TKE）の生成項を計算し，乱流計により得られたTKEの散逸率と比較すると，TKEの生成項と散逸項が混合層上部で均衡する結果を得た．一方，混合層下部ではTKEの散逸項が生産項を大きく上回っており，海氷の慣性振動による海洋上層での内部重力波の発生が要因として考えられる．
We conducted on-site investigations in the central Arctic Ocean about turbulent mixing and heat and salt transport in the sea ice-ocean boundary layer, related to the growth and melting of sea ice. During these observations, continuous measurements were performed beneath the sea ice while drifting with the icebreaker, RV Polarstern, providing insights into the spatiotemporal structure of water temperature, salinity, and turbulent mixing in the boundary layer associated with the periodic sea ice drift. Using an acoustic Doppler current profiler, the survey clearly captured the Ekman spiral in horizontal currents which rotate clockwise with the depth. The direct measurement of microscale current shear was conducted to estimate the production and dissipation terms of turbulent kinetic energy in the mixed layer. In its upper part, the two terms were well balanced. Meanwhile, in the lower part, the dissipation term significantly exceeded the production term, attributing to the near-inertial internal waves generated by the inertial oscillations of sea ice.
We conducted on-site investigations in the central Arctic Ocean about turbulent mixing and heat and salt transport in the sea ice-ocean boundary layer, related to the growth and melting of sea ice. During these observations, continuous measurements were performed beneath the sea ice while drifting with the icebreaker, RV Polarstern, providing insights into the spatiotemporal structure of water temperature, salinity, and turbulent mixing in the boundary layer associated with the periodic sea ice drift. Using an acoustic Doppler current profiler, the survey clearly captured the Ekman spiral in horizontal currents which rotate clockwise with the depth. The direct measurement of microscale current shear was conducted to estimate the production and dissipation terms of turbulent kinetic energy in the mixed layer. In its upper part, the two terms were well balanced. Meanwhile, in the lower part, the dissipation term significantly exceeded the production term, attributing to the near-inertial internal waves generated by the inertial oscillations of sea ice.
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