Numerical Simulation Of Temporal And Spatial Variation Of Temperature-Salinity In The Changjiang Estuary And Its Adjacent Sea

Progress results about numerical model of temporal and spatial variation of temperature and salinity, especially in the Changjiang Estuary and its adjacent sea, are reviewed in this thesis. Based on the Environmental Fluid Dynamic Code (EFDC), a 3-D water temperature and salinity model was applied to the Changjiang estuary and its adjacent area. River discharge, tide, wind and solar radiation were considered in this model. The computed results were fairly consistent with the observed data in 2005 and 2006, which implies that the EFDC model can be applied to study the characteristics of temperature-salinity distributions at the Changjiang estuary and its adjacent sea.It can be analyzed from the results that the temperature isolines off the Changjiang estuary in summer are along the south-north direction, with high values nearshore and low values offshore; in the Changjiang estuary, the temperatures are diminishing from the estuary to the offshore along the direction of Changjiang Diluted Water (CDW). The characteristics of CDW are prominent in summer. The low-salinity surface water can reach out 123°E and has a trend of east expansion off the Changjiang estuary. The intensities of themocline and halocline are extremely high at the area of CDW, which reach the values of 0.3℃/m and 2/m, respectively. The positions of thermocline and halocline are coincident or close-by off the Changjiang estuary.Water temperature in autumn is 6℃lower than in summer totally, and its distributions are contrary to those in summer, which are low values nearshore and high values offshore. The salinity isolines off the Changjiang estuary in autumn are from the east-west direction, which are similar with those in summer, but the area of the CDW reduces outside that in summer.The distributions of surface temperature and salinity in winter are consistent with those of bottom's distributions. The temperatures are increasing from the estuary to the offshore. In the Zhoushan Sea areas have the temperature grads due to the intrusion of the outer sea, but temperature in other sea areas is vertical mixing well. Compared with the distributions of salinity in summer, the salinity isolines move inside, and the low salinity water tongue is obviously shrinking. In the bottom salinity distribution there is obvious saltwater intrusion in the lower North Branch in the Changjiang Estuary.In spring the distributions of temperature are similar than those in summer, with high values in west and low values in east, high values in south and low values in north and the averaged values are about 18℃. The vertical variations of temperature are mainly focused on the middle layer and the phenomenon of thermocline appears in spring. Because of the increase of river discharge, the CDW extends quickly to the outer sea, along the Changjiang Estuary axes straight forward to the east-south direction. Most profiles show that the halocline develops well except the profile of 32°N.The haloclines of Changjiang Estuary and its adjacent sea are prominent in most seasons except in winter. The thermoclines exist off the Changjiang Estuary during summer, mainly in 10 meters from the sea surface; in spring the thermocline appears but not distinct.The distributions and variations of temperature in Changjiang Estuary and its adjacent areas are mainly influenced by the Changjiang river discharge, solar radiation and other weather factors, while the distributions and variations of salinity are mainly affected by the Changjiang river discharge and outer sea currents, which show distinct characteristics in different time scale.The model provided in this paper and the results of the model can lay a foundation for further study the environment capacity of the Changjiang Estuary and its adjacent sea.