Water discharge variability of Changjiang （Yangtze） and Huanghe （Yellow） Rivers and its response to climatic changes     

张喜林  范德江  王厚杰  杨作升 《中国海洋湖沼学报》2014,32(6):1392-1405

Influences of large-scale climatic phenomena, such as the E1Nifio/La Nifia-Southem Oscillation （ENSO） and the Pacific Decadal Oscillation （PDO）, on the temporal variations of the annual water discharge at the Lijin station in the Huanghe （Yellow） River and at the Datong station in the Changjiang （Yangtze） River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis （EMD- MESA） method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the inter- annual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.  相似文献   

Modeling seasonal variations of subsurface chlorophyll maximum in South China Sea   总被引：1，自引：0，他引：1  

Xiang Gong  Jie Shi  Huiwang Gao 《中国海洋大学学报(英文版)》2014,13(4):561-571

In the South China Sea(SCS), the subsurface chlorophyll maximum(SCM) is frequently observed while the mechanisms of SCM occurrence have not been well understood. In this study, a 1-D physical-biochemical coupled model was used to study the seasonal variations of vertical profiles of chlorophyll-a(Chl-a) in the SCS. Three parameters(i.e., SCM layer(SCML) depth, thickness, and intensity) were defined to characterize the vertical distribution of Chl-a in SCML and were obtained by fitting the vertical profile of Chl-a in the subsurface layer using a Gaussian function. The seasonal variations of SCMs are reproduced reasonably well compared to the observations. The annual averages of SCML depth, thickness, and intensity are 75 ± 10 m, 31 ± 6.7 m, and 0.37 ± 0.11 mg m-3, respectively. A thick, close to surface SCML together with a higher intensity occurs during the northeastern monsoon. Both the SCML thickness and intensity are sensitive to the changes of surface wind speed in winter and summer, but the surface wind speed exerts a minor influence on the SCML depth; for example, double strengthening of the southwestern monsoon in summer can lead to the thickening of SCML by 46%, the intensity decreasing by 30%, and the shoaling by 6%. This is because part of nutrients are pumped from the upper nutricline to the surface mixed layer by strong vertical mixing. Increasing initial nutrient concentrations by two times will increase the intensity of SCML by over 80% in winter and spring. The sensitivity analysis indicates that light attenuation is critical to the three parameters of SCM. Decreasing background light attenuation by 20% extends the euphotic zone, makes SCML deeper(~20%) and thicker(12% – 41%), and increases the intensity by over 16%. Overall, the depth of SCML is mainly controlled by light attenuation, and the SCML thickness and intensity are closely associated with wind and initial nitrate concentration in the SCS.  相似文献   

Warmer-Get-Wetter or Wet-Get-Wetter? A Criterion to Classify Oceanic Precipitation     

Chengcheng Qian  Ge Chen 《中国海洋大学学报(英文版)》2014,13(4):552-560

In this study, the temporal and spatial variations of observed global oceanic precipitation during 1979–2010 are investigated. It is found that the global trend in precipitation during this period varies at a rate of 1.5%/K of surface warming while the rate is 6.6%/K during 2006–2010. The precipitation is highly correlated with Sea Surface Temperature(SST) in both the temporal and the spatial patterns since the strong 1997–98 El Nino event. Considering the distributions of precipitation and SST, seven oceanic regions are classified and presented using the observed Global Precipitation Climatology Project(GPCP) data and Extended Reconstructed Sea Surface Temperatures, version 3(ERSST.v3) data. Further examining the mechanisms of the classified oceanic precipitation regions is conducted using the Tropical Rainfall Measuring Mission(TRMM) satellite, GFDL-ESM-2G model precipitation and SST data and Hadley Center sea ice and SST version 1(Had ISST1) data. More than 85% of global oceanic precipitations are controlled by either one or both of the warmer-get-wetter mechanism and wet-get-wetter mechanism. It is estimated that a 0.5 SST signal-to-noise ratio, representing the trend of SST time series to the standard deviation, is a criterion to distinguish the mechanism of a region. When the SST ratio is larger than 0.5, the precipitation of this region is controlled by the warmer-get-wetter mechanism. SST, rather than the humidity, is the pivotal factor. On the other hand, when the SST ratio is less than 0.5, the precipitation is controlled by the wet-get-wetter mechanism. The SST variability is a significant factor contributing to the precipitation variation.  相似文献   

条件平差和间接平差模型应满足的两个等式关系     

张俊  袁亮  张鹏飞 《测绘与空间地理信息》2014,(12)

条件平差和间接平差法是两种最基本的测量数据处理的方法,在整个工科数据处理中得到了广泛应用.但是,实践中,一些工程人员对这两种平差方法的区别与联系并不十分了解.本文基于最小二乘准则解的本质,推导出了条件平差法与间接平差法系数阵和常数项间应满足的两个等式关系,有助于广大工程人员理解这两种测量平差的本质与联系.  相似文献   

基于试验的模拟月壤表层取样理论修正及其应用          下载免费PDF全文

李谦  段隆臣  高辉 《探矿工程》2014,41(9):75-80

月球探测对于我国各方面综合实力的提升均具有巨大的推动作用。当前我国各研发机构对月球采样的研发重点集中于采样机具的设计制造上,对采样机具和月壤之间相互作用却研究较少。与地球土壤相比,月壤的形成环境与条件完全不同,从而造就了其较为特殊的物理力学性质。在利用与真实月壤类似的模拟月壤进行的薄壁圆筒贯入试验中,发现存在月壤滞留和月壤附壁现象,从而分析得出在采样机具表面与月壤相互作用的理论分析中,除了传统的摩擦力理论外,还可通过最大抗剪强度进行分析。通过对试验现象和数据对比摩擦力理论和最大抗剪强度理论发现,最大抗剪强度理论更加符合实际情况。故将最大抗剪强度理论引入已有的月球螺旋钻进采样的理论模型中,通过计算得出基于最大抗剪强度理论计算的螺旋临界转速低于基于摩擦力理论计算的临界转速,在一定程度上能够降低采样机具的能耗。  相似文献   

基于高阶统计的时变子波估计及其应用     

张  ;曹思远  ;郑晓东  ;路交通 《物探与化探》2014,(5):989-995

地震子波估计是地震资料高分辨处理、解释的基础,快速准确地估计地震子波具有重要意义。笔者利用三谱估计子波的振幅谱,根据峰度最大值准则提取子波的相位,规避了相位的卷绕问题,并讨论了该准则的适用条件。比较了不同窗函数的特性,最终选定Hamming窗函数滑动求取时变子波。利用变频雷克子波模型讨论了时变子波提取的有效性。应用到实际资料处理中,与不同主频的雷克子波标定的地震记录进行对比分析。结果表明:该方法使得子波振幅谱估计更加稳定,相位谱估计更易于实现,与实际情况更加符合。  相似文献   

Directional spread parameter at intermediate water depth     

V. Sanil Kumar  M. C. Deo  N. M. Anand  K. Ashok Kumar 《Ocean Engineering》2000,27(8):93

The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information.  相似文献   

应用数值模拟方法探讨河口最大浑浊带若干机理   总被引：1，自引：0，他引：1  

倪培桐  吴超羽  陈卓英 《热带海洋学报》2000,19(2):27-32

利用平面二维潮流方程结合悬沙输运方程模拟了河口最大浑浊带现象。并且对河口边界进行进一步概化 ,比较了恒定流与非恒定流、稳定源与非稳定源、矩形河口与线性河口等不同条件下河口悬沙浓度的平面分布特点。结果表明河口地形边界和非恒定潮流作用对河口最大浑浊带的悬沙富集有重要贡献。  相似文献   

厦门海域渔业资源评估   总被引：7，自引：0，他引：7  

卢振彬 《热带海洋学报》2000,19(2):51-56

以初级生产力和渔业统计资料为材 ,分别应用Tait沿岸海域生态系能流分析法、营养动态法和Cushing等 3种模式 ,估算厦门沿岸海域的渔业资源自然生产量。同时 ,分别应用Schaefer和Fox两种剩余产量模式估算最大持续产量和最大持续捕捞力量。前 3种模式估算该海域的资源生产量分别为 2 0 1 0 5t,1 8463t和 1 7489t,平均 1 8686t。后两种模式估算最大持续产量平均值分别为 9639t和 91 0 4t。估算的最大持续捕捞力量 :5种作业综合总功率为 1 5976kW ;以厦门机定置渔船单位功率渔捞效率为标准估算的总功率为 2 7351kW ;以厦门机刺网渔船单位功率渔捞效率为标准估算的总功率为 432 1 3kW。 1 997年实际渔获量和捕捞力量均超过了估算的最大持续产量和最大持续捕捞力量。文中还讨论了捕捞力量的调整问题。  相似文献   

农田近地表风沙流风程效应变化特征研究          下载免费PDF全文

冯哲  刘瑞娟  白宇晨  常春平  郭中领  李继峰  王仁德  李庆 《干旱区地理》2022,45(5):1500-1512

风沙流的风程效应研究是定量获取风沙流沿程变化的核心和难点,风程效应是指输沙率随沙床表面或地块长度的增加而不断增大,而后趋于稳定的变化特征,饱和输沙率（f_max）和饱和路径长度（L_sat）是风程效应的重要参数。采用自动连续称重式集沙仪,以河北坝上地区康保县境内典型旱作农田为研究对象,观测了2017、2018年和2021年内4次典型风蚀事件,分析近地表5 cm高度风沙流的风程效应在5 min时间尺度下的变化特征。结果表明：（1） 近地表输沙通量随风程距离的增大而增大。（2） 4次风蚀事件中L_sat的变化范围在11~280 m之间,并存在明显差异,其变化与风速无关。（3） 近地表风沙流的f_max与风速（U）呈幂函数关系。（4） 风程效应的变化特征与地表可蚀性因子、地表微地貌变化有着紧密联系,未来应对不同的土壤类型和质地农田的风程效应进行深入研究。  相似文献