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1.
A three-dimensional numerical model is used to simulate sea level and velocity variations in the South China Sea for 1992–1995. The model is driven by daily wind and daily sea surface temperature fields derived from the NCEP/NCAR 40-year reanalysis project. The four-year model outputs are analyzed using time-domain Empirical Orthogonal Functions (EOF). Spatial and temporal variations of the first two modes from the simulation compare favorably with those derived from satellite altimetry. Mode 1, which is associated with a southern gyre, shows symmetric seasonal reversal. Mode 2, which contributes to a northern gyre, is responsible for the asymmetric seasonal and interannual variations. In winter, the southern and northern cyclonic gyres combine into a strong basin-wide cyclonic gyre. In summer, a cyclonic northern gyre and an anticyclonic southern gyre form a dipole with a jet leaving the coast of Vietnam. Interannual variations are particularly noticeable during El Niño. The winter gyre is generally weakened and confined to the southern basin, and the summer dipole structure does not form. Vertical motions weaken accordingly with the basin-wide circulation. Variations of the wind stress curl in the first two EOF modes coincide with those of the model-derived sea level and horizontal velocities. The mode 1 wind stress curl, significant in the southern basin, coincides with the reversal of the southern gyre. The mode 2 curl, large in the central basin, is responsible for the asymmetry in the winter and summer gyres. Lack of the mode 2 contribution during El Niño events weakens the circulation. The agreement indicates that changes in the wind stress curl contribute to the seasonal and interannual variations in the South China Sea.  相似文献
2.
台湾以东黑潮流量的年际变化特征   总被引:15,自引:2,他引:13       下载免费PDF全文
利用长时间序列的石垣和基隆两个验潮站的海平面高度记录(18年)计算了台湾以东的黑潮流量,并结合风应力资料(SODA),探讨了台湾以东黑潮流量的年际变化及其和风应力旋度的关系。台湾以东黑潮流量的峰值出现在1980—1981、1982—1983、1986、1988及1991年。低值出现在1984、1990、1993—1995年。小波分析结果显示,台湾以东黑潮流量具有2—5年的显著周期(峰值在2年和5年);台湾以东北太平洋区域风应力旋度具有2—7年的显著周期(峰值在3年和6年)。在1980—1991年间,黑潮大弯曲频繁发生,台湾以东黑潮流量偏大,与台湾以东太平洋区域风应力旋度间的关系较好;而在1991—1995年间,没有黑潮大弯曲发生,台湾以东黑潮流量偏低,与台湾以东太平洋区域风应力旋度间的关系较差。  相似文献
3.
热带大西洋年际和年代际变率的时空结构模拟   总被引:12,自引:3,他引:9       下载免费PDF全文
使用美国夏威夷大学发展的中等复杂程度海洋模式(IOM)在给定表面强迫条件下模拟了热带大西洋上层海洋年际和年代际变率的时空结构,利用NCEP的41a(1958~1998年)逐月平均表面资料作为强迫场,积分海洋模式41a作为控制试验,并利用模式分别做动量(风应力)通量和热量通量无异常变化的平行试验,与控制试验作比较.对3组试验模拟上层海洋变率状况的比较,并按年际和年代际时间尺度分别分析,揭示表面风应力和热通量异常对海表面温度和温跃层深度变化的影响,并比较了其影响的相对重要性。结果表明模式成功地模拟出了热带大西洋上层海洋的变率.模式模拟的海表面温度年际变化主要表现为弱ENSO型,年代际变化表现为南、北大西洋变化相反的偶极子型。在年际时间尺度上,热力强迫和动力强迫对海表温度变化都有贡献,其中赤道外海表面温度异常(SSTA)变化主要由热通量异常引起,而近赤道SSTA的变化主要由动量异常强迫引起.在年代际时间尺度上,热通量强迫的作用远比动量强迫重要.模式不仅能够模拟SST在年际和年代际时间尺度上的变率,还能够模拟温跃层深度在年际和年代际时间尺度上的变率.年际和年代际时间尺度上,温跃层深度的变率主要由动量异常决定,热通量异常强迫的贡献很小。  相似文献
4.
南海大尺度动力场年循环和年际变化   总被引:10,自引:2,他引:8  
应用COADS风应力、Levitus温度资料,描述南海上层海洋动力场的年循环及其与热力场之间的关系和南海大尺度动力场的年际变化。针对冬、夏2个季节,分析Sverdrup环流场与上层海温之间的关系。研究发现,上层海温变化与上层海洋环流基本结构非常相似,即上层海温变化在一定程度上反映了南海Sverdrup平衡,而且随着浓度的增加,平均海温场与流函数场之间的对应关系更好。本文还着重分析了El Nino期间和La Nina期间的南海异常流函数场。研究发现,异常流函数场在El Nino期间的夏季主要是强化南海自身的环流结构,即强化南部反气旋式涡流(gvre)和强化北部气旋式涡流;冬季则削弱整个南海的气旋式流场。LaNina期间对夏季环流态的影响主要集中在南海北部,即削弱北部气旋式涡流,而对于南海南部的影响甚微;冬季则强化整个南海的气旋式流场。  相似文献
5.
山东夏季气温年际变化形成的气候特征   总被引:6,自引:0,他引:6  
为研究本地区短期气候预测方法,利用山东80个代表站夏季平均气温、降水量资料和NCEP/NCAR月平均再分析资料(1961~2001年),分析了夏季平均气温年际变化的气候特征、冷暖夏的环流形势及夏季风与气温的关系。结果表明:EOF第一模态几乎反映了整个温度场的时空变化特征;夏季气温标准化距平年际变化显著,有弱线性增温趋势;极端冷、暖夏大气环流形势差异明显,显著差异区在亚欧一北太平洋地区,冷夏年中高纬度欧亚大陆存在正欧亚一太平洋(EUP)型遥相关,东亚地区有负太平洋-日本(PJ)型波列,暖夏年反之。东亚夏季风强弱与山东夏季气温关系密切,强(弱)夏季风时,易造成山东暖(冷)夏;同期降水对气温有负反馈,对气温升高有一定的抑制作用。  相似文献
6.
渤海动力环境研究应关注的新问题   总被引:5,自引:0,他引:5  
回顾了近几年关于渤海动力环境的研究现状,分析了其中存在的问题。指出渤海盐度长期变化、年际尺度上变化的成因、过程;与此关联的渤海环流乃至黄海环流的变异及其过程;黄河入海的水、沙变化所引起发的渤海沉积物源汇的再调整等应是未来渤海动力环境研究中值得关注的重要问题。  相似文献
7.
Quarterly data of CTD at the PN line in the East China Sea during 1988–94 were analyzed to examine the variations of water properties and density structure in relation to the Kuroshio. The Kuroshio flows over the continental slope at the PN line. Water properties in the surface layer less than 100 db change greatly and show a clear seasonal cycle, while those in the subsurface layer are much less variable. The small isobaric variations in the subsurface layer are almost due to the vertical movement of isopycnals, on which the water properties vary little. The subsurface variations of salinity, temperature and isopycnal depth are classified into four groups occurring in the four regions, divided vertically by the middle of the main pycnocline and horizontally by the offshore edge of the Kuroshio, named Groups 1 (upper Kuroshio), 2 (upper offshore region), 3 (lower Kuroshio), and 4 (lower offshore region). The difference in averaged isopycnal depth between Groups 1 and 2 (3 and 4) is highly correlated with the vertical shear of the Kuroshio velocity in the upper (lower) pycnocline. The isopycnal depth of Groups 1 and 3 has little annual cycle (with large intraseasonal variations in Group 3), while that of Groups 2 and 4 shows a clear seasonal variation with the minimum in fall. As a result, the Kuroshio velocity is smallest in fall almost every year, although the amplitude of seasonal variation and the season of maximum velocity are different from year to year. Interannual variations of isopycnal depth are characterized by a large amplitude of Group 2 and an opposite phase between Groups 3 and 4, so that the variations of difference in isopycnal depth between Groups 1 and 2 and Groups 3 and 4, i.e., the upper and lower shear of the Kuroshio velocity, are comparably significant.  相似文献
8.
Interannual variations of sea level at the Nansei Islands and volume transport of the Kuroshio during 1967–95 are calculated by integrating variations carried by windforced Rossby waves. Effects of eddy dissipation and ocean ridges are considered. Ridge effect is inferred by comparing between the calculated and observed sea levels. The calculation is satisfactory to sea levels and Kuroshio transport for the whole period. They are mostly caused by Rossby waves forced by wind and modified by the ridges, and are due to barotropic wave primarily and the first baroclinic wave secondly. The calculated Kuroshio transport well represents variations of several-year scales with maximums in respective duration of the large meander (LM) of the Kuroshio, as well as bi-decadal variation that transport was small during the non-LM period of 1967–75 and large during the LM-dominant period of 1975–91. Mean volume transport of the subtropical gyre is estimated at 57 Sv (1 Sv = 106 m3s–1) and divided by the Nansei Shoto Ridge into those of the Kuroshio in the East China Sea (25.5 Sv) and a subsurface current east of this ridge (31.5 Sv). The Subtropical Countercurrent and a southward deep current east of the Izu-Ogasawara Ridge are estimated at 16 Sv and 7 Sv, respectively. The calculated transports of the Kuroshio and other subtropical currents reach maximums at every El Niño event due to strong excitement of upwelling barotropic Rossby wave.  相似文献
9.
A singular value decomposition (SVD) analysis is carried out to reveal the relationship between the interannual variation of track and intensity of the western North Pacific tropical cyclones (WNPTCs) in the tropical cyclone (TC) active season (July-November) and the global net air-sea heat flux (Q net ) in the preceding season (April-June). For this purpose, a tropical cyclone track and intensity function (TIF) is defined by a combination of accumulated cyclone energy (ACE) index and a cyclone track densit...  相似文献
10.
关于南海暖水季节和年际变化的研究   总被引:3,自引:3,他引:0  
阐述了研究南海暖水的意义 ,综述了关于南海暖水的现状 ,提出了关于南海暖水季节和年际变化方面应该研究的问题  相似文献
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