2:00 PM - 2:15 PM
[AOS18-08] Extraction of the path of Kuroshio Extension using reanalysis data
Keywords:Kuroshio Extention, Kuroshio, Ocean physics
When the Kuroshio passes around Mikurajima, the flow pattern of the Kuroshio Extension (KE)is relatively stable. On the other hand, when KE passes south of Hachijojima (non-meandering offshore flow path), the flow pattern of KE is unstable (Qiu and Chen (2005); Sugimoto and Hanawa (2012)).
Modulations in the flow pattern of the KEhave been explained by the combination of the Aleutian Low, PDO anomalies andbaroclinicRossby wave propagation, which have almost the same fluctuation period, but after 2017, these fluctuation period don’t match and this interpretation is considered to be reset(Qiu et al. (2020)).
Therefore, we assumed the pattern of KE is determined by vorticity mode and the growth of baroclinic instability wave. We had numerical experiment by the CDmodel which is able to show the growth of resonant wave of upper and lower layer as vorticity boundary with minimum condition for baroclinic instability to be occur, which is two-layer quasi-geostrophic flow. As a result KE is stable under long wave and andgreater difference in the vortex boundary position between the upper and lower layers.We gave a new interpretation to the behavior of patterns of KE by wave mechanics with this CDmodel(Shimada, Suzuki (2023)).
In this study, zonal and meridional flows of MOVE/MRI.COM-JPN Dataset (Sakamoto et al., 2019) from 2008 to 2019 are used in order to show whether this mechanism is functioning or not in the real. The horizontal grid size of this dataset is 2 km. The upper- and lower-layer are defined as the mean of 1 to 200 m (24 layers) and 212.5 to 1212.5 m (19 layers). The Kuroshio axis is defined as 1) the grid where the velocity is maximized in Izu Ridge, 139.75 degrees east, from 32 to 35 degrees north; 2) the grid where the velocity interpolated as 2-km grid is maximized in the 10-km width downstream of 2 km from the previous grid. This method is similar to Anbe et al. (2004) and Osaki et al. (2009). In the previous studies, the Kuroshio axis from Quick Bulletin of Ocean Condition that is subjective analysis is used. In this study, we obtained the Kuroshio axes of upper- and lower-layer through the objective analysis. This study shows the overview of the variability of the Kuroshio axis and discussed the relationship of the zonal wavelength of KE and the stability of the path of KE.
Modulations in the flow pattern of the KEhave been explained by the combination of the Aleutian Low, PDO anomalies andbaroclinicRossby wave propagation, which have almost the same fluctuation period, but after 2017, these fluctuation period don’t match and this interpretation is considered to be reset(Qiu et al. (2020)).
Therefore, we assumed the pattern of KE is determined by vorticity mode and the growth of baroclinic instability wave. We had numerical experiment by the CDmodel which is able to show the growth of resonant wave of upper and lower layer as vorticity boundary with minimum condition for baroclinic instability to be occur, which is two-layer quasi-geostrophic flow. As a result KE is stable under long wave and andgreater difference in the vortex boundary position between the upper and lower layers.We gave a new interpretation to the behavior of patterns of KE by wave mechanics with this CDmodel(Shimada, Suzuki (2023)).
In this study, zonal and meridional flows of MOVE/MRI.COM-JPN Dataset (Sakamoto et al., 2019) from 2008 to 2019 are used in order to show whether this mechanism is functioning or not in the real. The horizontal grid size of this dataset is 2 km. The upper- and lower-layer are defined as the mean of 1 to 200 m (24 layers) and 212.5 to 1212.5 m (19 layers). The Kuroshio axis is defined as 1) the grid where the velocity is maximized in Izu Ridge, 139.75 degrees east, from 32 to 35 degrees north; 2) the grid where the velocity interpolated as 2-km grid is maximized in the 10-km width downstream of 2 km from the previous grid. This method is similar to Anbe et al. (2004) and Osaki et al. (2009). In the previous studies, the Kuroshio axis from Quick Bulletin of Ocean Condition that is subjective analysis is used. In this study, we obtained the Kuroshio axes of upper- and lower-layer through the objective analysis. This study shows the overview of the variability of the Kuroshio axis and discussed the relationship of the zonal wavelength of KE and the stability of the path of KE.