The Research On The Eddy In The Northern South China Sea And Circulation In The Beibu Gulf

Firstly, the characteristics of eddies and their effects on the circulation in thenorthern South China Sea (SCS) were examined, basis on the Sea Level Anomalydata and developed eddy-detected method. Secondly, the three-dimensionalhindcast model was built in the northwestern SCS and the effects of SCScirculation and other factors on the circulation in the Beibu Gulf were analyzed.The findings were mainly as follows:Based on the Okubo-Weiss method, six procedures were added to avoid thenoise, which could achieve the robust results. In addition, four distinctive sinks ofthe eddy (EAAs) were firstly examined, which were linked with the four eddybirthplaces to result in four pathways for eddies in the northern SCS.The zonal distribution of the eddy kinetic energy flux (EKEF) was alsofigured out, with two peaks in the eastern and western boundary, respectively. Andthe westward EKEF was almost6times as the eastward EKEF. Compared with thework on the circulation by the wind, the work by eddies was almost night times asthat in the northern SCS. The eddy would be generated and dissipatedcontinuously along the westward propagation way. Thus, the eddy acted as a relayto transfer the energy from east to west, and the energy would be lastlyaccumulated in the western boundary.The eddy could affect the Beibu Gulf via the SCS circulation. However, thecirculation in the Gulf has not been agreed in the past twenty years, which was dueto the limited in situ data and diagnostic numerical models in the past. Therefore,the three-dimensional hindcast model was built in the northwestern SCS, modelingthe circulation in the Beibu Gulf between2006and2007. This numerical modelconsidered the daily averaged blended wind and heat flux (OAFlux Project) data,and six tidal consituents from tidal model of OSU. For the lateral boundaries, the daily averaged temperature, salinity, barotropic and baroclinic velocities, andelevation were constructed from HYCOM between December1,2005andDecember31,2007. And the monthly averaged river discharges were alsospecified. As a result, the model results were consistent with in situ data, such asthe current observation data. And two upwellings and two cold water masses weremodeled as the observation result of Project908.With the good model results, the new views were concluded: it could beshowed an apparent seasonal evolution in the southern Gulf: in summer thevertically averaged circulation was anti-cyclonic, whereas in winter the patternchanged to cyclonic. The circulation was dominated by outer SCS circulation andnortheasterly wind in summer and winter, respectively. In the northern Gulf flowswere independent between the eastern and the western side. The flows in thenorthwestern interior Gulf were affected jointly by several currents including thecoastal plume and the branch separated from the southern gyre, resulting in noapparent seasonal variation. However, the northeastern Gulf was dominated by thelocal wind and the flows from the QS.Different water masses were distinguished at the surface with the warm andsaline South China Sea water in the south, relatively fresh plume waters along thenorthern and western coasts of the Gulf, and the mixture of the two in between.They were adjusted by wind and heat flux. Such as, the warm and saline SCSwater could intrude the Beibu Gulf more northward without heat flux. In addition,the river plume in the western Gulf was modulated by the river discharge and wind,which was pushed towards the shore in winter but spread offshore in summer. Atlower levels, two cold, water masses were found in the model, which wereproduced throughout the winter, sheltered and protected from the surface warmingby a thermocline as the season progressed, and gradually disappeared fromsummer to fall. These two cold water masses were dominant by the heat flux, andwind played second role.By placing the model open boundary east of the Pearl River delta and allowing sufficient resolution of the Qiongzhou Strait (QS), flows in the QS weredetermined. Because the daily variation was at least as strong as the seasonalcurrent, flows in the QS could be westward or eastward on some days in summeror winter, but the seasonal mean current was eastward from late spring throughsummer and westward during the rest of the year, with an annual mean westwardtransport of~0.1Sv (~) into the Gulf.The characteristics and mechanisms of upwellings and warm pool wereexamined in the Beibu Gulf. The upwelling off western coast of Hainan wasdominated by tidal mixing and heat flux, while the southwesterly wind hadnegative effect on it; the upwellings off Vietnamese coast and off southern coast ofHainan were induced by the Ekman transport of southwesterly wind. In addition,there was warm pool existing between October and January off the western coastof Hainan, induced by the latent heat flux and vertical mixing by the northesterlywind.Basis on this work, the research of marine biogeochemistry and fishery willbe carried out. In addition, it is helpful to the protection of marine environment offcoasts of Guangxi and Hainan.