High Frequency(HF) radar current data is assimilated into a shelf sea circulation model based on optimal interpolation(OI) method. The purpose of this work is to develop a real-time computationally highly efficient as...High Frequency(HF) radar current data is assimilated into a shelf sea circulation model based on optimal interpolation(OI) method. The purpose of this work is to develop a real-time computationally highly efficient assimilation method to improve the forecast of shelf current. Since the true state of the ocean is not known, the specification of background error covariance is arduous. Usually, it is assumed or calculated from an ensemble of model states and is kept in constant. In our method, the spatial covariances of model forecast errors are derived from differences between the adjacent model forecast fields, which serve as the forecast tendencies. The assumption behind this is that forecast errors can resemble forecast tendencies, since variances are large when fields change quickly and small when fields change slowly. The implementation of HF radar data assimilation is found to yield good information for analyses. After assimilation, the root-mean-square error of model decreases significantly. Besides, three assimilation runs with variational observation density are implemented. The comparison of them indicates that the pattern described by observations is much more important than the amount of observations. It is more useful to expand the scope of observations than to increase the spatial interval. From our tests, the spatial interval of observation can be 5 times bigger than that of model grid.展开更多
The northern South China Sea(NSCS) is a dynamically complex region whose shelf and slope currents are driven by different mechanisms. In this study, we used field measurements to identify clear interannual variations ...The northern South China Sea(NSCS) is a dynamically complex region whose shelf and slope currents are driven by different mechanisms. In this study, we used field measurements to identify clear interannual variations in the circulation related to the El Ni?o-Southern Oscillation cycle. To investigate the modulation mechanisms, we used a high-resolution numerical model that covers the shelf and slope regions of the NSCS. The results indicate that the stronger southwestward slope current during La Ni?a and stronger northeastward shelf current during El Ni?o in summer and winter are largely related to changes in wind forcing. The Kuroshio intrusion into the NSCS does not appear to significantly affect the circulation in the southwestern shelf region.展开更多
Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical result...Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical results of the δ￣(18) O are as follows: (1) In the Kuroshio area, the δ￣(18) o isolines are almost parallel to the200 m isobath. The value of δ￣(18)O is nagative and reaches minimum on the main axis of the Kuroshio,and increases on both sides. (2) In the Taiwan Warm Current (TWC) area there is a high δ￣(18) O tongue extending to the northeast. (3)In the area near the coast, the distribution of δ￣(18)O isoline shows that the Changjiang River runoff diffuses seaward andthe land-ocean isotopic effect from the nearshore to the offshore. (4) The values of δ￣(18) O are from-1. 0 x 10￣(-3) to -0.5 x 10￣(-3) in the shelf. (5) There is a low core of δ￣(18) O value (< -1 .6 X 10￣(-3)) at the 600 m layer in the Kuroshioarea, which is quite in accord with the ekistence of a low salinity core (S 34. 30) between the 600 and 800 m layersin the same area. Finally, the correlations of the δ￣(18)O with the salinity and temperature, the upwelling and so on arediscussed.(This study was supported by the National Natural Science Foundation of China under contract No. 4907257.)Yuan Yaochu et al. The Northwest Pacific circulation and its impacts on the current near the Chinese coast, 1991-1993.展开更多
基金supported by the State Oceanic Administration Young Marine Science Foundation (No. 2013201)the Shandong Provincial Key Laboratory of Marine Ecology and Environment & Disaster Prevention and Mitigation Foundation (No. 2012007)+1 种基金the Marine Public Foundation (No. 201005018)the North China Sea Branch Scientific Foundation (No. 2014B10)
文摘High Frequency(HF) radar current data is assimilated into a shelf sea circulation model based on optimal interpolation(OI) method. The purpose of this work is to develop a real-time computationally highly efficient assimilation method to improve the forecast of shelf current. Since the true state of the ocean is not known, the specification of background error covariance is arduous. Usually, it is assumed or calculated from an ensemble of model states and is kept in constant. In our method, the spatial covariances of model forecast errors are derived from differences between the adjacent model forecast fields, which serve as the forecast tendencies. The assumption behind this is that forecast errors can resemble forecast tendencies, since variances are large when fields change quickly and small when fields change slowly. The implementation of HF radar data assimilation is found to yield good information for analyses. After assimilation, the root-mean-square error of model decreases significantly. Besides, three assimilation runs with variational observation density are implemented. The comparison of them indicates that the pattern described by observations is much more important than the amount of observations. It is more useful to expand the scope of observations than to increase the spatial interval. From our tests, the spatial interval of observation can be 5 times bigger than that of model grid.
基金supported by the National Key Research and Development Program of China (No. 2016YFC1401604)the National Natural Science Foundation of China (No. 41806035)+5 种基金the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)(No. GML2019ZD0305)the National Natural Science Foundation of China (Nos. 4173053641890805)the Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences (No. ISEE2019ZR02)the Guangdong Basic and Applied Basic Research Foundation (No. 2019A1515012108)the Research Funds from the State Key Laboratory of Tropical Oceanography (No. LTOZZ1803)。
文摘The northern South China Sea(NSCS) is a dynamically complex region whose shelf and slope currents are driven by different mechanisms. In this study, we used field measurements to identify clear interannual variations in the circulation related to the El Ni?o-Southern Oscillation cycle. To investigate the modulation mechanisms, we used a high-resolution numerical model that covers the shelf and slope regions of the NSCS. The results indicate that the stronger southwestward slope current during La Ni?a and stronger northeastward shelf current during El Ni?o in summer and winter are largely related to changes in wind forcing. The Kuroshio intrusion into the NSCS does not appear to significantly affect the circulation in the southwestern shelf region.
文摘Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical results of the δ￣(18) O are as follows: (1) In the Kuroshio area, the δ￣(18) o isolines are almost parallel to the200 m isobath. The value of δ￣(18)O is nagative and reaches minimum on the main axis of the Kuroshio,and increases on both sides. (2) In the Taiwan Warm Current (TWC) area there is a high δ￣(18) O tongue extending to the northeast. (3)In the area near the coast, the distribution of δ￣(18)O isoline shows that the Changjiang River runoff diffuses seaward andthe land-ocean isotopic effect from the nearshore to the offshore. (4) The values of δ￣(18) O are from-1. 0 x 10￣(-3) to -0.5 x 10￣(-3) in the shelf. (5) There is a low core of δ￣(18) O value (< -1 .6 X 10￣(-3)) at the 600 m layer in the Kuroshioarea, which is quite in accord with the ekistence of a low salinity core (S 34. 30) between the 600 and 800 m layersin the same area. Finally, the correlations of the δ￣(18)O with the salinity and temperature, the upwelling and so on arediscussed.(This study was supported by the National Natural Science Foundation of China under contract No. 4907257.)Yuan Yaochu et al. The Northwest Pacific circulation and its impacts on the current near the Chinese coast, 1991-1993.
