17:15 〜 19:15
[AOS18-P02] Interannual Developmental Cycles of the Mixed Layer in the Eastern North Pacific
キーワード：大気海洋相互作用、海洋表層混合層、北太平洋、風応力
The mixed layer in the upper ocean is the only boundary layer in the ocean that directly interfaces with the atmosphere and is recognized as the principal field for air–sea interactions. In particular, elucidating the drivers of climate change requires understanding how the interannual variability of water masses in the upper ocean—mediated by the mixed layer—affects the heat exchange processes between the atmosphere and the ocean.
In this study, we focus on upper ocean in the North Pacific, investigating the development of the mixed layer and the interannual variability of wind during winter. For our analysis, we employed the ARMOR3D dataset provided by CMEMS for water temperature and density data and the JRA55-do reanalysis from the Japan Meteorological Agency for wind stress data. First, the mixed layer depth was computed using two distinct definitions: one based on water temperature—defined as the depth at which the temperature deviates by 0.2°C from the values in the upper 10 m—and the other based on density—defined as the depth at which the density differs by 0.125σ from those in the upper 10 m. Next, we analyzed the interannual variations in water mass characteristics and wind stress curl fields at the time when the mixed layer reached its maximum depth during winter.
Our results reveal that, within middle region of the eastern North Pacific, the wintertime development of the mixed layer is persistently suppressed over many years, with the same region exhibiting an asymmetric development cycle over time. Moreover, when comparing years with extreme (local maximum and local minimum) development of the mixed layer, a reversal in the sign of the surface wind stress curl is observed. These statistical results suggest that the development of the mixed layer and the latitudinal variation of the zero contour of wind stress curl may be synchronized.
At the time of the presentation, we also plan to discuss in detail the atmospheric influences and internal oceanic processes that contribute to the development of the mixed layer.
In this study, we focus on upper ocean in the North Pacific, investigating the development of the mixed layer and the interannual variability of wind during winter. For our analysis, we employed the ARMOR3D dataset provided by CMEMS for water temperature and density data and the JRA55-do reanalysis from the Japan Meteorological Agency for wind stress data. First, the mixed layer depth was computed using two distinct definitions: one based on water temperature—defined as the depth at which the temperature deviates by 0.2°C from the values in the upper 10 m—and the other based on density—defined as the depth at which the density differs by 0.125σ from those in the upper 10 m. Next, we analyzed the interannual variations in water mass characteristics and wind stress curl fields at the time when the mixed layer reached its maximum depth during winter.
Our results reveal that, within middle region of the eastern North Pacific, the wintertime development of the mixed layer is persistently suppressed over many years, with the same region exhibiting an asymmetric development cycle over time. Moreover, when comparing years with extreme (local maximum and local minimum) development of the mixed layer, a reversal in the sign of the surface wind stress curl is observed. These statistical results suggest that the development of the mixed layer and the latitudinal variation of the zero contour of wind stress curl may be synchronized.
At the time of the presentation, we also plan to discuss in detail the atmospheric influences and internal oceanic processes that contribute to the development of the mixed layer.