The time evolution of the general circulation over the South China Sea and surrounding areas during the period from April to June is studied using ECMWF data of 1980-1986. The first transition from the second (6-10 M...The time evolution of the general circulation over the South China Sea and surrounding areas during the period from April to June is studied using ECMWF data of 1980-1986. The first transition from the second (6-10 May ) to the third (11-15 May ) pentads is characterized by the distinct change of low-level (850 hpa ) winds from southeasterlies to southwesterlies along 15°N over the South China Sea, and by the sudden movement of the center of South Asian high in the upper troposphere (200 hpa ) from 10-15°N to 15-20°N over Southeast Asia. Corresponding to the abrupt change in circulations, the gradients of the temperature and humidity intensity along latitudes center on 30°N over East Asia at 850 hpa. The time sequence of the 850- 200 hpa layer thickness shows that the layer-mean temperature over the southeastern Tibetan Plateau-East China Plain region increases abruptly at the same time. The corresponding sudden increase of the vertically integrated heat source (Q1 )over the warming areas reveals that the heat source plays an evident role in the drastic changes. The time series of (Q1 ) over the northern part of the South China Sea shows that the drastic increase of the areamean (Q1 ) is also found but it is 5-10 days late than the change of corresponding wind fields. The time series of Xisha SST shows a continuous increase to about 29. 5°until May 10 when the abrupt changes in circulation occur.展开更多
In petroleum seismic exploration,dense seismic ray coverage is often guaranteed through dense seismic sources and geophones.Dense ray coverage facilitates the high-resolution 3D velocity structure imaging of near surf...In petroleum seismic exploration,dense seismic ray coverage is often guaranteed through dense seismic sources and geophones.Dense ray coverage facilitates the high-resolution 3D velocity structure imaging of near surfaces using surface waves.In this study,the 3D velocity and anisotropy structure of a petroleum exploration area are obtained using the azimuth-dependent dispersion curve inversion(ADDCI)method.Imaging results show that low-velocity zones correspond to a river channel.The fast propagation direction(FPD)of S-waves along this channel is basically consistent with the direction of the channel.The eastern part of the study area has a surface sediment layer with a thickness of less than 20 m,which corresponds to the sand and gravel deposits formed by the river alluvial deposition near the surface.In addition,a relatively thick sedimentary layer is formed on the southern side of the study area.The anisotropy shows that the FPD is positively correlated with the direction of alluvial fl ow and that the magnitude of anisotropy in the deep part is greater than that in the shallow part.Inversion results are basically consistent with the geological data and suggest that the obtained model can truly refl ect the 3D velocity structure and anisotropy of the near-surface area.This study shows that the ADDCI method can maximize the high-energy surface waves in exploration data to obtain near-surface velocity structures,which provide a highly accurate model for near-surface static correction.展开更多
文摘The time evolution of the general circulation over the South China Sea and surrounding areas during the period from April to June is studied using ECMWF data of 1980-1986. The first transition from the second (6-10 May ) to the third (11-15 May ) pentads is characterized by the distinct change of low-level (850 hpa ) winds from southeasterlies to southwesterlies along 15°N over the South China Sea, and by the sudden movement of the center of South Asian high in the upper troposphere (200 hpa ) from 10-15°N to 15-20°N over Southeast Asia. Corresponding to the abrupt change in circulations, the gradients of the temperature and humidity intensity along latitudes center on 30°N over East Asia at 850 hpa. The time sequence of the 850- 200 hpa layer thickness shows that the layer-mean temperature over the southeastern Tibetan Plateau-East China Plain region increases abruptly at the same time. The corresponding sudden increase of the vertically integrated heat source (Q1 )over the warming areas reveals that the heat source plays an evident role in the drastic changes. The time series of (Q1 ) over the northern part of the South China Sea shows that the drastic increase of the areamean (Q1 ) is also found but it is 5-10 days late than the change of corresponding wind fields. The time series of Xisha SST shows a continuous increase to about 29. 5°until May 10 when the abrupt changes in circulation occur.
基金supported by the National Key Research and Development Program of China(No.2017YFC0601206)the Science and Technology Innovation(Seedling Project)Cultivation Program of Sichuan Province in 2020(No.2020127)the National Natural Science Foundation of China(Nos.41674059,41340009)。
文摘In petroleum seismic exploration,dense seismic ray coverage is often guaranteed through dense seismic sources and geophones.Dense ray coverage facilitates the high-resolution 3D velocity structure imaging of near surfaces using surface waves.In this study,the 3D velocity and anisotropy structure of a petroleum exploration area are obtained using the azimuth-dependent dispersion curve inversion(ADDCI)method.Imaging results show that low-velocity zones correspond to a river channel.The fast propagation direction(FPD)of S-waves along this channel is basically consistent with the direction of the channel.The eastern part of the study area has a surface sediment layer with a thickness of less than 20 m,which corresponds to the sand and gravel deposits formed by the river alluvial deposition near the surface.In addition,a relatively thick sedimentary layer is formed on the southern side of the study area.The anisotropy shows that the FPD is positively correlated with the direction of alluvial fl ow and that the magnitude of anisotropy in the deep part is greater than that in the shallow part.Inversion results are basically consistent with the geological data and suggest that the obtained model can truly refl ect the 3D velocity structure and anisotropy of the near-surface area.This study shows that the ADDCI method can maximize the high-energy surface waves in exploration data to obtain near-surface velocity structures,which provide a highly accurate model for near-surface static correction.
