11:00 AM - 1:00 PM
[AOS17-P03] Frontogenesis of the Tsushima Warm Current: an impact to turbulent-scale phenomena
Keywords:Frontogenesis, Deformation flow, Mixing, Intensive survey, Reanalysis dataset, The Tsushima Warm Current
Evolution of density fronts caused by large-scale and mesoscale deformation flow, called frontogenesis, is one of the submesoscale phenomena. Previous studies have pointed out that the frontogenesis plays a role in energy cascade from mesoscale to microscale current. Water mass rapidly elongated along the front due to frontogenesis often forms filament structure with properties different from those of the surrounding water masses. Filaments broken by the shear of horizontal flow have been suggested to enhance effective mixing by increasing the gradient of water mass properties. However, since comprehensive observations that resolve submesoscale to microscale current are limited, evaluation of evolution process of frontogenesis and energy transport process and understanding of mixing process between scales based on observation data are still insufficient.
The surface layer of the Tsushima Warm Current (TWC) frontal region, which flows along the northern coast of Japan, has large kinetic energy due to variation of the TWC path and the existence of mesoscale eddies. With the TWC front as the boundary, warm and saline (cold and fresh) water is in the south (north) of the TWC frontal region. In this study, to examine the submesoscale deformation process and water mass structure as well as the associated mixing process in the TWC frontal region, we conducted a high-density survey using a profiler (VMP-250). At the same time, we analyzed the Japan coastal ocean reanalysis dataset (MOVE MRI.COM-JPN Dataset; Meteorological Research Institute) to follow the evolution process of the density front due to the deformation flow.
Horizontal flow obtained by the shipboard acoustic Doppler current profiler (ADCP) showed the convergence in the cross-frontal direction, consistent with the satellite sea surface height. Warm and saline TWC water was thick in the surface layer near the TWC front. Below the warm and saline water, patches of cold and fresh water with a horizontal scale of 30–50 km were found. According to the reanalysis dataset, the density gradient of the TWC front increased in the deformation field, suggesting that frontogenesis occurred in the observed area. In relation to the deformation field, the large dissipation rate of turbulent kinetic energy seemed to be recognized. On the other hand, the dissipation rate of the temperature variance increased with the intrusive pattern such as the subsurface patches of cold and fresh water. By analyzing the observed data along with the reanalysis dataset, we described the submesoscale process frontogenesis and resulting water mass structure in the TWC region, and considered the contribution of turbulent mixing.
The surface layer of the Tsushima Warm Current (TWC) frontal region, which flows along the northern coast of Japan, has large kinetic energy due to variation of the TWC path and the existence of mesoscale eddies. With the TWC front as the boundary, warm and saline (cold and fresh) water is in the south (north) of the TWC frontal region. In this study, to examine the submesoscale deformation process and water mass structure as well as the associated mixing process in the TWC frontal region, we conducted a high-density survey using a profiler (VMP-250). At the same time, we analyzed the Japan coastal ocean reanalysis dataset (MOVE MRI.COM-JPN Dataset; Meteorological Research Institute) to follow the evolution process of the density front due to the deformation flow.
Horizontal flow obtained by the shipboard acoustic Doppler current profiler (ADCP) showed the convergence in the cross-frontal direction, consistent with the satellite sea surface height. Warm and saline TWC water was thick in the surface layer near the TWC front. Below the warm and saline water, patches of cold and fresh water with a horizontal scale of 30–50 km were found. According to the reanalysis dataset, the density gradient of the TWC front increased in the deformation field, suggesting that frontogenesis occurred in the observed area. In relation to the deformation field, the large dissipation rate of turbulent kinetic energy seemed to be recognized. On the other hand, the dissipation rate of the temperature variance increased with the intrusive pattern such as the subsurface patches of cold and fresh water. By analyzing the observed data along with the reanalysis dataset, we described the submesoscale process frontogenesis and resulting water mass structure in the TWC region, and considered the contribution of turbulent mixing.