A model for the transportation and distribution of jellyfish Rhopilema esculentum for stock enhancement in the Liaodong Bay, China

A numerical model for jellyfish Rhopilema esculentum stock enhancement is developed for the first time. The model is based on an operational ocean circulation-surface wave coupled forecasting system for the seas off China and adjacent areas and uses a Lagrangian particle-tracking scheme to track the trajectories of released jellyfish. The Jellyfish are modeled as particles with diel vertical migration and are passively drifted by the current and dispersion due to the sub-grid processes. A comparison between the simulation and survey results demonstrate that the model can capture the primary distribution patterns of the released jellyfish. The model results show that the ocean current and indirect wind impact are the main drivers controlling the jellyfish transport. A connectivity matrix between the release sites and fishing grounds indicates the top of the bay is better than the eastern and western coasts for jellyfish fishing. The matrix also shows that only 45% and 27% of the jellyfish released from Wafangdian(WFD) can enter the fishing ground in 2008 and 2010; thus, the site near WFD is not an advisable location for jellyfish release. A Lagrangian probability density function based on a nine-year tracing experiment validates the results and further provides a "climatology" distribution of the released jellyfish.Several experiments are conducted to examine the sensitivity of the model to random walk schemes and to release conditions. The model requires a random walk but is insensitive to the random walk scheme. The experiments with different habitat depths show that if the jellyfish are fixed on the bottom of the water, most of them will be transported to the center, or even out of the bay, by the bottom circulation.

The summertime circulation of the Bohai Sea simulated from a high-resolution wave-tide-circulation coupled model

The Bohai Sea is a shallow semi-enclosed inner sea with an average depth of 18 m and is located at the west of the northern Yellow Sea. The climatological circulation pattern in summer of the Bohai Sea is studied by using a wave-tide-circulation coupled model. The simulated temperature and the circulation agree with the observation well. The result shows that the circulation pattern of the Bohai Sea is jointly influenced by the tidal residual current, wind and baroclinic current. There exists an obvious density current along the temperature front from the west part of the Liaodong Bay to the offshore area of the Huanghe Estuary. In the Liaodong Bay there exists a clockwise gyre in the area north to the 40°N. While in the area south to the 40°N the circulation shows a two-gyre structure, the flow from the offshore area of the Huanghe Estuary to the Liaodong Bay splits into two branches in the area between 39°N and 40°N. The west branch turns into north-west and forms an anti-clockwise gyre with the south-westward density current off the west of the Liaodong Bay. The east branch turns to the east and forms a clockwise gyre with the flow along the east coast of the Liaodong Bay. The forming mechanism of the circulation is also discussed in this paper.

China published ocean forecasting system for the 21st-Century Maritime Silk Road on December 10, 2018

1 The unique ocean forecasting system (OFS) based on FIO-COM The OFS is based on the surface wave-tide-circulation coupled ocean model developed by the First Institute of Oceanography (FIO-COM), Ministry of Natural Resources, China. The half-century challenge that ocean circulation models must address is that the forecasting/simulated sea surface temperature overheats while the sub-surface temperature is too cold, especially during the summer. Qiao et al.(2004, 2010, 2016) found that the non-breaking surface wave can generate turbulence through wave-turbulence interaction, and they developed the wave-induced mixing theory, which has been confirmed by observations, laboratory experiments and model numerical simulations. As validated by ocean circulation models from various research groups, including Geophysical Fluid Dynamics Laboratory (GFDL) in the US (Fan and Griffies, 2014), Uppsala University of Sweden (Wu et al., 2015), Laboratoire d’Etudes en Geophysique et Oceanographie Spatiale (LEGOS) in France (Malek and Babanin, 2014), Budapest University of Technology and Economics in Hungary (Peter and Kramer, 2016) and the Ocean University of China (Lin et al., 2006), the non-breaking surface waveinduced vertical mixing (Bv) can always dramatically improve the simulation capacity of various ocean circulation models. The First Institute of Oceanography (FIO) research group found that tidal-induced mixing plays a key role in the formation of coastal upwelling, in the bottom mixed layer and in areas with sea mounts (Lv et al., 2006, 2008). With the above breakthroughs, the first surface wavetide-circulation coupled model of FIO-COM was developed in 2013. It was adopted to produce a reanalysis dataset for the period of January 2014 to April 2016, and it has been used for the operational OFS since May 2016. A highly efficient parallel scheme was designed to use the full capacity of Taihu Light with 10 649 600 CPU cores (Qiao et al., 2016), which earned a finalist nomination for the international Association for Computing Machinery (ACM) Gordon Bell Prize.

Geostrophic Spirals Generated by the Horizontal Diffusion of Vortex Stretching in the Yellow Sea

Horizontal velocity spirals with a clockwise rotation(downward looking) rate of 1.7?m^(-1), on average, were observed in the western and northern Yellow Sea from December 2006 to February 2007. With the observed thermal wind relation,the beta-spiral theory was used to explain the dynamics of spirals. It was found that the horizontal diffusion of geostrophic vortex stretching is likely to be a major mechanism for generating geostrophic spirals. Vertical advection associated with surface/bottom Ekman pumping and topography-induced upwelling is too weak to support these spirals. Strong wind stirring and large heat loss in wintertime lead to weak stratification and diminish the effects of vertical advection. The cooling effect and vertical diffusion are offset by an overwhelming contribution of horizontal diffusion in connection with vortex stretching. The Richardson number-dependent vertical eddy diffusivity reaches a magnitude of 10^(-4) m^2 s^(-1) on average. An eddy diffusivity of 2870 m^2 s^(-1) is required for dynamic balance by estimating the residual term. This obtained value of 10-4 m^2 s^(-1) is in good agreement with the estimation in terms of observed eddy activities. The suppressed and unsuppressed diffusivities in the observation region are 2752 and 2881 m^2 s^(-1), respectively, which supports a closed budget for velocity rotation.

The mechanism of the banded structure of drifting macroalgae in the Yellow Sea

At the end of May 2008,a massive bloom of macroalgae occurred in the western Yellow Sea off China and lasted for nearly two months,and annual blooms have occurred since then on. During bloom period,the surface-drifting macroalgae have showed an interesting pattern dominated by a banded structure,and the distance between neighboring bands ranged from hundreds of meters to about 6 km with a peak at 1–1.5 km,which is an order of higher than the scale of Langmuir circulation of 50–100 m. In order to explain this new phenomenon,ocean current data obtained from a Doppler current profiler off Qingdao was used to implement stability analysis. By numerically solving the resulting differential Orr-Sommerfeld equation,the secondary circulation induced from the instability of the Emkan current was found to fit well with the observed spatial scale of the surface-drifting macroalgae’s banded structure. As the wind driven Emkan current exist universally in the global ocean,it is reasonable to conclude that the banded structure with kilometers distance between adjoining bands is ubiquitous. We found a new circulation in the upper ocean which is important for exchange of energy,materials and gas between the upper ocean and subsurface layer.

Effects of different freshwater flux representations in an ocean general circulation model of the tropical Pacific

Freshwater flux(FWF) is a major forcing that affects the ocean through several processes. The effects of FWF may be represented in ocean modeling as real freshwater flux(RFF) formulations and virtual salt flux(VSF) methods. RFF formulations have been implemented in the Geophysical Fluid Dynamics Laboratory(GFDL) Modular Ocean Model version 5(MOM5) as a replacement for the non-physical VSF method, which is primarily used in state-of-the-art ocean models. Here, we systematically evaluated the effects of RFF-related processes on the GFDL MOM5-based simulations in the tropical Pacific.When the FWF was treated as the natural boundary condition(NBC), it directly decreased the local temperature and the salinity by changing the volume of the top model layer, and it increased the temperature in the eastern Pacific by triggering an eastward Goldsbrough–Stommel circulation in the subsurface.Moreover, the heat content induced by the FWF tended to counteract the decreasing effects of the NBC on sea surface temperatures(SSTs) in the western-central tropical Pacific. The relationships between SST perturbations and the FWF representation in ocean modeling are also discussed.

The effects of the non-breaking surface wave-induced vertical mixing on the forecast of tropical cyclone tracks

The Weather Research and Forecasting model(WRF)is configured for the region of(15°–41°N,105°–135°E),which covers the same area with the MASNUM(Key Lab.Marine Science&Numerical Modeling,State Oceanic Administration)wave-tide-circulation coupled operational forecast system.Three numerical experiments are implemented to investigate the effects of the real-time forecasted sea surface temperature(SST)and the nonbreaking wave-induced vertical mixing(Bv)on the track forecast of all 33 tropical cyclones(TC)in the model domain area during 2008 and 2011.The first experiment employs NCEP FNL(NCEP final analysis)SST as WRF’s bottom condition as the Control run,which is also the default setup of WRF.The second and third experiments use real-time forecasted SST from the MASNUM forecast system with and without Bv,respectively.The forecasted track results are compared with Japan Meteorological Agency’s best track data.For 24-h forecast,the averaged TC position error of Experiment with Bv is reduced by 9%compared to the Control experiment,while the forecasted track error of Experiment without Bv is reduced by only2%compared to the Control experiment.For the 48-h forecast,the averaged track errors are reduced by 10%and6%with Bv and without Bv compared to the Control experiment,respectively.These results suggest that the real-time forecasted SST can improve the performance of WRF in forecasting TC track,and the Bv plays an important role in reducing the forecast error of TC track.Comparatively,Bv can improve more on the track of stronger TC.