| Climate change has been to be a decisive and significance issue in today’s era. Ocean plays a vital role in the climate system. The water exchange between the Northwest Pacific and the South China Sea is important for the climate change, ecology and economy of the coastal areas in our country and other countries, which has become a hot issue of current research. The Luzon Strait is the only deep-water channel of the water exchange between the Northwest Pacific and the South China Sea, which has become a hot research area. As the only deep-water channel of the water exchange between the Northwest Pacific Ocean and the South China Sea, The Luzon Strait has become a hot research area. It is one of the major scientific issues of the core program of the World Climate Research Programme(WCRP) to reveal the seasonal and interannual variability, and the change trends of the mean climate state of ocean in the monsoon zone. Research on the water exchange in the Luzon Strait, focuses mainly on the upper water exchange and its impact mechanism, and in a short period, and so on.In this paper, the Luzon Strait is as the study area, and 120°E section is as the research section. The spatial and temporal changes of the temperature, salt and flow in the Luzon Strait are studied. The influence of monsoon, the sea surface height, ENSO and other factors on the water exchange of layers in the Luzon Strait is also discussed. The specific research contents and results are as following:(1)Based on the data of the flow, temperature and salinity, and the EOF spatial analysis and the correlation analysis are used. The net average transport of volume, heat and salt from January to December are calculated at all layers. The distribution change of the flow, temperature and salinity of water exchange at the vertical layers in the Luzon Strait is discussed. The monthly and seasonal variation of the net transport of volume, heat and salt, and their structure is explored. The water of the South China Sea flows eastward into the Pacific Ocean in each month throughout the year, in the area as deep as more than 300 m in south of 21.5°N, and less than 1000 m in north of 21.5°N. Almost all the net transports of volume, heat and salt at the upper, the deeper and the full depth layers, flow westward into the South China Sea and show the maximum in winter, followed by spring and autumn, and with the minimum in summer. Almost all the net transports of volume, heat and salt at the middle layer, flow eastward into the Pacific Ocean in each month throughout the year and show the maximum in spring, followed by summer and autumn, with the minimum in winter.(2)About the net transport structure, the structure change of the net volume and salt transport is more consistent and shows three different types. The net transport structure at the entire section shows a sandwich structure from January to May and from August to November, the net transport of volume and salt flows westward into the South China Sea at the upper and the deeper layers, and the net transport of volume and salt flows eastward into the Pacific Ocean in the middle layer. The net transport structure of volume and salt at the entire section shows a two-layer structure in June and July, the net transport of volume and salt flows westward into the South China Sea at the upper layer, and the net transport of volume and salt flows eastward into the Pacific Ocean at the middle and the deeper layers. The net transport structure of volume and salt at the entire section shows a single-layer structure in December, the net transport of volume and salt flows westward into the South China Sea at the upper layer, the middle layer and the deeper layer. The annual average transport structure of volume and salt at the entire section shows a sandwich structure. The sandwich structure of volume and salt transport is predominant, and the net transport structure of volume and salt also appears the two-layer structure and the single-layer structure throughout the year. The structure change of the net volume and salt transport is not entirely consistent in each month.The structure change of the net heat transport shows four different types. The net transport structure of heat at the entire section shows a sandwich structure from January to May and September, the net heat transport flows westward into the South China Sea at the upper and the deeper layers, and the net heat transport flows eastward into the Pacific Ocean at the middle layer. The net transport structure of heat at the entire section shows a single-layer structure in June, the net heat transport flows eastward into the Pacific Ocean at the upper layer, the middle layer and the deeper layer. The net transport structure of heat at the entire section shows a two-layer structure in July and August, the net heat transport flows westward into the South China Sea at the upper layer and flows eastward into the Pacific Ocean at the middle and the deeper layers. The net transport structure of heat at the entire section shows a single-layer structure in from October to December, the net heat transport flows westward into the South China Sea at the upper layer, the middle layer and the deeper layer. The annual average transport structure of heat at the entire section shows a sandwich structure. The sandwich structure of the net heat transport is predominant, and also shows the two-layer structure and the single-layer structure throughout the year. The structure change of the net heat transport is not entirely consistent in each month.The net transport of volume, heat and salt at each layer in December flows westward into the South China Sea. The sandwich structure of the net volume, heat and salt is predominant. But the structure change of the net of volume, heat and salt transport in each month, and among the net transport structure of volume, heat and salt, are not entirely consistent.(3)Based on the data of the flow, temperature and salinity, the linear regression analysis and curve fitting methods are used. The net transport of volume, heat and salt in each month from 1993 to 2006 are calculated. The long-term change features and change rate are analyzed. The wavelet decomposition and de-noising filtering methods are used to discuss the change trends at all layers. The wavelet transform method is used to discuss the specific change cycle.The net transport of volume, heat and salt in each month from 1993 to 2006 flows westward into the South China Sea, which is predominant at the upper layer, the deeper layer and the entire section. The net transport of volume, heat and salt, flows eastward into the Pacific Ocean, which is predominant at the middle layer.The net volume transport flows eastward into the Pacific Ocean and shows a declining trend at upper layer, the middle layer and the entire section. The net volume transport flows westward into the South China Sea and shows an increasing trend. The change rates of the net volume transport at the upper layer, the middle layer and the entire section are 0.0129Sv/m, 0.008Sv/m and 0.0003Sv/m separately. At the deeper layer, the change rate is 0.02Sv/m and shows the opposite trend with the other layers.At the upper layer, the middle layer and the entire section, the net heat transport flows eastward into the Pacific Ocean and shows a declining trend. The net heat transport flows westward into the South China Sea and shows an increasing trend. The change rates at the upper layer, the middle layer and the entire section are 0.0009 PW/m, 0.0003 PW/m and 0.0007 PW/m separately. At the deeper layer, the change rate is 0.0004 PW/m and shows the opposite trend with the other layers.At the upper layer, the middle layer and the entire section, the net salt transport flows eastward into the Pacific Ocean and shows a declining trend. The net salt transport flows westward into the South China Sea and shows an increasing trend. The change rates at the upper layer, the middle layer and the entire section are 0.456 Gg/s/m, 0.273 Gg/s/m and 0.011 Gg/s/m separately. At the deeper layer, the change rate is 0.718 Gg/s/m and shows the opposite trend with the other layers.(4)The net transport of volume, heat and salt in each month from 1993 to 2006, flows westward into the South China Sea at the upper layer, the deeper layer and the entire section, the maximum of them are all in winter. The net transport of volume flows eastward into the Pacific Ocean at the middle layer, the maximum of it is in summer and spring. The net transport of volume at all layers shows a strong seasonal variation, and a significant three-month period, which is particularly significant at the upper layer and the entire section.(5)Based on the data of the flow, temperature and salinity, the linear regression analysis is used, the net average transports of volume, heat and salt in each year from 1993 to 2006 are calculated.The net average volume transport in each year from 1993 to 2006, the net average volume transport flows westward into the South China Sea at the upper layer and increases by 0.155 Sv per year. The net average volume transport flows eastward into the Pacific Ocean at the middle layer and decreases by 0.085 Sv per year. The net average volume transport flows westward into the South China Sea at the deeper layer and the entire section, which decreases by 0.251 Sv and 0.011 Sv per year separately.The net average heat transport in each year from 1993 to 2006, the net average heat transport flows westward into the South China Sea at the upper layer and the entire section, which increases by 0.011 PW and 0.008 PW per year separately. The net average heat transport flows eastward into the Pacific Ocean at the middle layer from 1993 to 2001 and in 2006, which decreases by 0.003 PW per year. The net average heat transport flows westward into the South China Sea at the middle layer from 2001 to 2005 and increases by 0.003 PW per year. The net average heat transport flows westward into the South China Sea at the deeper layer and decreases by 0.006 PW per year.The net average salt transport in each year from 1993 to 2006, the net average salt transport flows westward into the South China Sea at the upper layer and increases by 5.463 Gg/s per year. The net average salt transport flows eastward into the Pacific Ocean at the middle layer and decreases by 2.963 Gg/s per year. The net average salt flows westward into the South China Sea at the deeper layer and the entire section, which decreases by 8.807 Gg/s and 0.381 Gg/s separately.(6)Based on the data of the flow, temperature and salinity, wind field, sea surface height, ENSO and so on, the correlation analysis and spatial analysis are used. The net average transport of volume and heat, volume and salt, are significantly correlated, at the upper, middle, deeper layer and the entire section from January to December, which from January to December each year from 1993 to 2006 are also significantly correlated, which of the average transport in each year from 1993 to 2006 are significantly correlated too. The correlation of the monsoon and the net transport of volume, heat and salt at the upper layer and the entire section is significant. The correlation of the monsoon and the net heat transport at the middle layer is also significant. The correlation of the monsoon and the net transport of volume and salt at the middle layer is not significant. Monsoon has no significant impacts on the net transport of volume, heat and salt at the deeper layer.The sea surface height field obviously reflects the spatial variation of the flow pattern each month from January to December at the upper layer in the Luzon Strait.The correlation coefficient of the SST index in the Nino3.4 area and the net transport of volume, heat and salt at the upper layer exceeded the 98% confidence level test, when the net transport of volume, heat and salt lag the SST index in the Nino3.4 area 4-8 months. In particular, when the net transport of volume, heat and salt lag the SST index in the Nino3.4 area 6 months, the correlation coefficients of them are the largest. The correlation coefficients of them are 0.277, 0.264 and 0.277 respectively, which are positively correlated with ENSO. The net transport of volume, heat and salt lag ENSO about six months at the upper layer. The correlation coefficient of the SST index in the Nino3.4 area and the net transport of volume, heat and salt, do not exceeded the 98% confidence level test at the middle, the deeper layer and the entire section. |
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