一般认为, 吕宋海峡北南两端压力梯度或深度积分的动力高度差是太平洋水通过吕宋海峡西侵南海最直接的动力学。这一动力高度差与吕宋岛西部外海气旋式中尺度涡(即吕宋冷涡, Luzon cold eddy, LCE)的季节性出现有关, 而LCE活跃区上空正的风应力旋度(wind stress curl, WSC)在LCE的产生中起主要作用。基于上述思路, 利用涡分辨力海洋环流模式OFES[oceanic general circulation model (OGCM) for the Earth Simulator]的62年(1950—2011)后报结果首先得出吕宋海峡水体输运量(Luzon Strait transport, LST)不仅有约3年和7年显著的年际振荡, 而且有约14年显著的年代际变化。然后分析LCE活跃区上空WSC异常场主要模态低频振荡特征以寻找影响LST年际和年代际变化的局地因子。结果表明, 对LCE活跃区上空WSC去除季节性信号的异常场做经验正交函数(empirical orthogonal function, EOF)分析取得了典型的年际以上尺度的主要模态特征, 其第一模态时空变化表现为约14年显著的年代际振荡和WSC异常场正位相区年代际尺度上的南移, 而第二模态表现为约3年显著的年际振荡和WSC异常场正位相区年际尺度上的北移。另一方面, LST约7年的变化特征可视为源区黑潮水体输运量低频变化在该尺度上的印记。
Pressure gradient across the Luzon Strait, or depth-integrated dynamic height difference (DHD) between its northern end at the continental slope southwest of Taiwan and its southern end at the continental slope northwest of Luzon, is commonly regarded as the most direct dynamics of the intrusion of waters from the Pacific into the South China Sea through the Luzon Strait. Such a positive DHD is determined by seasonal occurrence of a meso-scale cyclonic cold eddy off west Luzon (Luzon cold eddy, LCE), and a positive wind stress curl (WSC) over the LCE active area or direct Ekman pumping may play a major role in generating the LCE. Based on the above ideas, prominent interannual (roughly 3 years and 7 years) and decadal (roughly 14 years) variability in the upper-layer Luzon Strait transport (LST) was first revealed using the 62-year (1950-2011) hindcast outputs from an eddy-resolving ocean general circulation model. To seek local factors affecting the interannual and decadal variability of LST, deseasonalized anomaly field of WSC over the LCE active area was analyzed using empirical orthogonal function (EOF). Dominant EOF modes of WSC anomaly were obtained. Spatio-temporal variability of the first EOF mode is of prominent decadal oscillation with a period of roughly 14.2 years and decadal southward shift of positive phase of the WSC anomaly, while the second EOF mode is of interannual oscillation of roughly 3.3 years and interannual northward shift of positive phase of the WSC anomaly. On the other hand, the near 7-year interannual oscillation was noticeable and can be regarded as an imprint of the variability of Kuroshio volume transport at its origin.
[1] 方国洪, 魏泽勋, 黄企洲, 等, 2002. 南海南部与外海间的体积和热、盐输运及其对印尼贯穿流的贡献[J]. 海洋与湖沼, 33(3): 296-302. FANG GUOHONG, WEI ZEXUN, HUANG QIZHOU, et al, 2002. Volume, heat and salt transports between the southern South China Sea and its adjacent waters, and their contribution to the Indonesian throughflow[J]. Oceanologia et Limnologia Sinica, 33(3): 296-302 (in Chinese with English abstract).
[2] 姜涛, 黄洪辉, 王文质, 2006. 吕宋海峡输送年际变异数值研究[J]. 热带海洋学报, 25(5): 13-20. JIANG TAO, HUANG HONGHUI, WANG WENZHI, 2006. A numerical study on interannual variations of Luzon Strait transports[J]. Journal of Tropical Oceanography, 25(5): 13-20 (in Chinese with English abstract).
[3] 刘秦玉, 杨海军, 李薇, 等, 2000. 吕宋海峡纬向海流及质量输送[J]. 海洋学报, 22(2): 1-8. LIU QINYU, YANG HAIJUN, LI WEI, et al, 2000. Velocity and transport of the zonal current in the Luzon Strait[J]. Acta Oceanologica Sinica, 22(2): 1-8 (in Chinese with English abstract).
[4] 孙成学, 刘秦玉, 2011. 卫星高度计资料揭示的冬季南海吕宋冷涡的双涡结构[J]. 热带海洋学报, 30(3): 9-15. SUN CHENGXUE, LIU QINYU, 2011. Double eddy structure of the winter Luzon Cold Eddy based on satellite altimeter data[J]. Journal of Tropical Oceanography, 30(3): 9-15 (in Chinese with English abstract).
[5] CHANG Y-L, OEY L-Y, 2012. The Philippines-Taiwan oscillation: monsoonlike interannual oscillation of the subtropical-tropical western north Pacific wind system and its impact on the ocean[J]. Journal of Climate, 25(5): 1597-1618.
[6] FANG GUOHONG, FANG WENDONG, FANG YUE, et al, 1998. A survey of studies on the South China Sea upper ocean circulation[J]. Acta Oceanographica Taiwanica, 37(1): 1-16.
[7] HSIN Y-C, WU C-R, CHAO S-Y, 2012. An updated examination of the Luzon Strait transport[J]. Journal of Geophysical Research, 117(C3): C03022.
[8] LAN JAN, BAO XIANWEN, GAO GUOPING, 2004. Optimal estimation of zonal velocity and transport through Luzon Strait using variational data assimilation technique[J]. Chinese Journal of Oceanology and Limnology, 22(4): 335-339.
[9] LIANG W-D, TANG T Y, YANG Y J, et al, 2003. Upper-ocean currents around Taiwan[J]. Deep Sea Research Part II: Topical Studies in Oceanography, 50(6-7): 1085-1105.
[10] LIU YONGGANG, YUAN YAOCHU, SU JILAN, et al, 2000. Circulation in the South China Sea in summer of 1998[J]. Chinese Science Bulletin, 45(18): 1648-1655.
[11] MASUMOTO Y, SASAKI H, KAGIMOTO T, et al, 2004. A fifty-year eddy-resolving simulation of the world ocean- preliminary outcomes of OFES (OGCM for the Earth Simulator)[J]. Journal of the Earth Simulator, 1: 35-56.
[12] QU TANGDONG, 2000. Upper-layer circulation in the South China Sea[J]. Journal of Physical Oceanography, 30(6): 1450-1460.
[13] QU TANGDONG, DU YAN, SASAKI H, 2006. South China Sea throughflow: a heat and freshwater conveyor[J]. Geophysical Research Letters, 33(23): L23617.
[14] QU TANGDONG, KIM Y Y, YAREMCHUK M, et al, 2004. Can Luzon Strait transport play a role in conveying the impact of ENSO to the South China Sea?[J]. Journal of Climate, 17(18): 3644-3657.
[15] SASAKI H, NONAKA M, MASUMOTO Y, et al, 2008. An eddy-resolving hindcast simulation of the quasi-global ocean from 1950 to 2003 on the earth simulator[M]// HAMILTON K, OHFUCHI W. High resolution numerical modelling of the atmosphere and ocean. New York: Springer, 157-185.
[16] SASAKI H, SASAI Y, KAWAHARA S, et al, 2004. A series of eddy-resolving ocean simulations in the world ocean-OFES (OGCM for the Earth Simulator) project[C]//Proceedings of Oceans'04. MTS/IEEE: Techno Ocean'04. Kobe, Japan: IEEE, 3: 1535-1541.
[17] SHAW P-T, 1991. The seasonal variation of the intrusion of the Philippine sea water into the South China Sea[J]. Journal of Geophysical Research: Oceans, 96(C1): 821-827.
[18] SHAW P-T, CHAO S-Y, LIU K-K, et al, 1996. Winter upwelling off Luzon in the northeastern South China Sea[J]. Journal of Geophysical Research, 101(C7): 16435-16448.
[19] SONG Y S, HU J-H, HO C-R, et al, 1995. Cold-core eddy detected in South China Sea[J]. EOS (Earth & Space Science News), 76(35): 345-347.
[20] WU C-R, HSIN Y-C, 2012. The forcing mechanism leading to the Kuroshio intrusion into the South China Sea[J]. Journal of Geophysical Research, 117(C7): C07015.
[21] WU C-R, 2013. Interannual modulation of the Pacific Decadal Oscillation (PDO) on the low-latitude western North Pacific[J]. Progress in Oceanography, 110: 49-58.
[22] YANG HAIJUN, LIU QINYU, 2003. Forced Rossby wave in the northern South China Sea[J]. Deep Sea Research Part I: Oceanographic Research Papers, 50(7): 917-926.
[23] YAREMCHUK M, QU TANGDONG, 2004. Seasonal variability of the large-scale currents near the coast of the Philippines[J]. Journal of Physical Oceanography, 34(4): 844-855.
[24] YU KAI, QU TANGDONG, 2013. Imprint of the Pacific decadal oscillation on the South China Sea throughflow variability[J]. Journal of Climate, 26(24): 9797-9805.
[25] ZHANG ZHIWEI, ZHAO WEI, TIAN JIWEI, et al, 2015. Spatial structure and temporal variability of the zonal flow in the Luzon Strait[J]. Journal of Geophysical Research: Oceans, 120(2): 759-776.
