2:15 PM - 2:30 PM
[AOS18-09] PIV analyses of sea-ice eddies observed in the Sea of Okhotsk off the Northeastern coast of Hokkaido
Keywords:sea ice, Sea of Okhotsk, ocean eddy, sea ice eddy
Southern edge of the Sea of Okhotsk, the area off the Northeastern coast of Hokkaido, is characterized by smoothly curved coastline elongating from Cape Soya to Cape Shiretoko through Cape Notori and submarine topography where a shallow continental shelf and a deep ocean basin are next to each other. There, complex flow pattern is formed due to the collision of the East Sakhalin current, which flows southward along the eastern coast Sakhalin, and the Soya warm current entering the Sea of Okhotsk through Soya strait. Then, oceanic vortices of various scales, both cyclonic and anti-cyclonic, are observed. These eddies are visualized with floating sea ice in winter since the area is the southern margin of seasonal sea ice in the northern hemisphere. It enables us to know the behavior of sea ice eddied by analyzing satellite and/or radar images. We attempt to derive velocity fields surrounding such eddies from visual imagery of GMS (Himawari) with the PIV technique.
Roughly three types of eddies are observed in the Sea of Okhotsk off the Northeastern coast of Hokkaido: i.e. anti-cyclonic eddies seen over Chishima basin (Wakatsuchi & Ohshima, 1990), cyclonic eddy streets along the northeastern coast of Hokkaido which is generated through barotropic instability, and a cyclonic eddy formed off the Shiretoko peninsula. At a glance, the second and third eddies are looked same, i.e. both eddies are formed along the northeastern coast of Hokkaido with 20 – 40 km offshore although the former and the latter eddies are observed upstream and downstream of the Soya warm current, respectively. However, we dare to distinguish them since the latter eddy is formed over the Chishima basin as an isolated eddy while the former eddies are formed over the continental shelf as eddy streets. In the present study, we mainly focus the case on 8 March in 2002 and that on 27 January in 2003. In addition to an anti-cyclonic eddy, barotropic eddy streets were simultaneously observed in the first case and a cyclonic eddy off the Shiretoko peninsula in the second case.
PIV analyses of satellite imagery shows cyclonic circulations associated with sea ice eddies, which were much larger than their apparent magnitude visualized by sea ice. Then, almost stationary backward breaking was detected as for barotropic eddy streets, which implies the existence of strong counter current offshore of the Soya warm current. Meanwhile, it was detected that a cyclonic eddy off the Shiretoko peninsula was, under the absence of the Soya warm current, generated in the center of cyclonic circulation which was formed by coastal current along curved coastline between Cape Notori and Cape Shiretoko. Since the coastal current was originated from the East Sakhalin Current from north, it is indicated that the cyclonic eddy off the Shiretoko Peninsula is completely different from barotropic eddy streets along the northeastern coast of Hokkaido, which were caused by shear between the Soya warm current and the offshore cold current.
Roughly three types of eddies are observed in the Sea of Okhotsk off the Northeastern coast of Hokkaido: i.e. anti-cyclonic eddies seen over Chishima basin (Wakatsuchi & Ohshima, 1990), cyclonic eddy streets along the northeastern coast of Hokkaido which is generated through barotropic instability, and a cyclonic eddy formed off the Shiretoko peninsula. At a glance, the second and third eddies are looked same, i.e. both eddies are formed along the northeastern coast of Hokkaido with 20 – 40 km offshore although the former and the latter eddies are observed upstream and downstream of the Soya warm current, respectively. However, we dare to distinguish them since the latter eddy is formed over the Chishima basin as an isolated eddy while the former eddies are formed over the continental shelf as eddy streets. In the present study, we mainly focus the case on 8 March in 2002 and that on 27 January in 2003. In addition to an anti-cyclonic eddy, barotropic eddy streets were simultaneously observed in the first case and a cyclonic eddy off the Shiretoko peninsula in the second case.
PIV analyses of satellite imagery shows cyclonic circulations associated with sea ice eddies, which were much larger than their apparent magnitude visualized by sea ice. Then, almost stationary backward breaking was detected as for barotropic eddy streets, which implies the existence of strong counter current offshore of the Soya warm current. Meanwhile, it was detected that a cyclonic eddy off the Shiretoko peninsula was, under the absence of the Soya warm current, generated in the center of cyclonic circulation which was formed by coastal current along curved coastline between Cape Notori and Cape Shiretoko. Since the coastal current was originated from the East Sakhalin Current from north, it is indicated that the cyclonic eddy off the Shiretoko Peninsula is completely different from barotropic eddy streets along the northeastern coast of Hokkaido, which were caused by shear between the Soya warm current and the offshore cold current.