A massive bloom of the giant jellyfi sh Nemopilema nomurai occurred in waters off Qinhuangdao,a port city in Hebei Province,in July 2013.However,jellyfi sh larvae were not found in this location during the previous wi...A massive bloom of the giant jellyfi sh Nemopilema nomurai occurred in waters off Qinhuangdao,a port city in Hebei Province,in July 2013.However,jellyfi sh larvae were not found in this location during the previous winter and spring.To determine the possible origin of the giant jellyfi sh medusa in the Bohai Sea,we developed a backward particle-tracking model and a series of numerical simulations were conducted by using the hydrodynamic,three-dimensional Regional Ocean Modeling System(ROMS)results.The simulated results showed that passive particles,representing jellyfi sh medusae,released in surface waters at diff erent dates during the summer had consistent trajectories.Particles released at the sea surface on August1 and 15 could be traced back to the center of the Bohai Sea and to waters between Feiyan Shoal and the new Huanghe(Yellow)River estuary.Particles released on July 1 and 15 could also be traced back to the center of the Bohai Sea and to waters between Feiyan Shoal and only to Zhuangxi tide station.However,none of the particles released in the middle and bottom water layers could be traced back to those areas.Based on the results of the numerical simulations,the distribution characteristics of seafl oor sediments,and observational data for giant jellyfi sh in the region,we suggest that waters between Feiyan Shoal and the new Huanghe River estuary are the likely origin of giant jellyfi sh observed near Qinhuangdao in summer.展开更多
Flow over a backward-facing step was studied to investigate the effect of large-scale vortex structures on sediment incipience. The transient flow velocity field at the downstream of the backward-facing step was obtai...Flow over a backward-facing step was studied to investigate the effect of large-scale vortex structures on sediment incipience. The transient flow velocity field at the downstream of the backward-facing step was obtained using the technique of Particle Tracking Velocimetry （PTV）. The optical amplification technique was employed to measure the instantaneous flow velocities near the bed and the instantaneous bed shear stress was given. The experimental observations revealed a new insight into the oscillation of the large-scale structure and the three-dimensional characteristics of the flow. In particular, very high turbulence intensity, instantaneous horizontal velocity near the bed and the bed shear stress near the reattachment point were observed. The sediment incipient probability obtained from the sequent images of sediment particles near the bed indicates that the critical instantaneous shear stress of the sediment incipience is independent of flow conditions.展开更多
基金Supported by the National Special Research Fund for Non-Profi t Marine Sector(No.201005018)the Open Fund of Key Laboratory of Ocean Circulation and Waves,Institute of Oceanology,Chinese Academy of Sciences(No.KLOCAW1403)
文摘A massive bloom of the giant jellyfi sh Nemopilema nomurai occurred in waters off Qinhuangdao,a port city in Hebei Province,in July 2013.However,jellyfi sh larvae were not found in this location during the previous winter and spring.To determine the possible origin of the giant jellyfi sh medusa in the Bohai Sea,we developed a backward particle-tracking model and a series of numerical simulations were conducted by using the hydrodynamic,three-dimensional Regional Ocean Modeling System(ROMS)results.The simulated results showed that passive particles,representing jellyfi sh medusae,released in surface waters at diff erent dates during the summer had consistent trajectories.Particles released at the sea surface on August1 and 15 could be traced back to the center of the Bohai Sea and to waters between Feiyan Shoal and the new Huanghe(Yellow)River estuary.Particles released on July 1 and 15 could also be traced back to the center of the Bohai Sea and to waters between Feiyan Shoal and only to Zhuangxi tide station.However,none of the particles released in the middle and bottom water layers could be traced back to those areas.Based on the results of the numerical simulations,the distribution characteristics of seafl oor sediments,and observational data for giant jellyfi sh in the region,we suggest that waters between Feiyan Shoal and the new Huanghe River estuary are the likely origin of giant jellyfi sh observed near Qinhuangdao in summer.
基金Project supported by the National Natural Science Foundation of China(Grant No.10602017).
文摘Flow over a backward-facing step was studied to investigate the effect of large-scale vortex structures on sediment incipience. The transient flow velocity field at the downstream of the backward-facing step was obtained using the technique of Particle Tracking Velocimetry （PTV）. The optical amplification technique was employed to measure the instantaneous flow velocities near the bed and the instantaneous bed shear stress was given. The experimental observations revealed a new insight into the oscillation of the large-scale structure and the three-dimensional characteristics of the flow. In particular, very high turbulence intensity, instantaneous horizontal velocity near the bed and the bed shear stress near the reattachment point were observed. The sediment incipient probability obtained from the sequent images of sediment particles near the bed indicates that the critical instantaneous shear stress of the sediment incipience is independent of flow conditions.
