Combined wavelet and principal component analysis (WEof) of a scale-oriented model of coastal ocean gravity waves     

Ivane Pairaud  Francis Auclair 《Dynamics of Atmospheres and Oceans》2005,40(4):22-282

Coastal ocean numerical modeling is basically the representation of the dynamics of the coastal ocean in a chosen range of length scales and over an associated frequency band, including the modeling of both coherent processes and associated transient processes. The ocean dynamical features can be individually identified by combining wavelet analysis for time and frequency localization and principal component analysis to “decorrelate” physically consistent structures. In the present paper, the so-called WEof analysis is applied for the extraction of external gravity waves and internal gravity wave lower modes in a simple case of a flat bottom, constant Brunt-Väisälä ocean. It is shown that, with some well known restrictive assumptions, WEof analysis is an efficient candidate for the recognition of frequency localized dynamical processes.  相似文献   

Statistical analysis of modern seed assemblages from the San Francisco Bay: applications for the reconstruction of paleo-salinity and paleo-tidal inundation     

Michelle Goman 《Journal of Paleolimnology》2001,26(4):393-409

The feasibility of developing a seed calibration data set to infer environmental constraints was examined by studying modern seed and vegetation assemblages from 53 stations at three distinct tidal marshes within the San Francisco Bay (salt, brackish and freshwater). Pearson's correlation indicates autochthonous derivation of seeds at the marsh sites. Multivariate statistical analysis of the vegetation and seed data indicates discrete assemblages, which can be used as a proxy for modern salinity and tidal inundation within the estuary. Canonical discriminant analysis indicates that the vegetation and seed assemblages of the three marsh types are statistically distinct. Cluster analysis suggests that marsh vegetation is zoned at the mean higher high water mark at all the sites. The calibration set was then applied to stratigraphic seed data from the estuary to infer changes in paleo-salinity and -tidal inundation during the Holocene. The results of the calibration are compared to earlier reconstructions within the estuary. While the calibrated reconstruction broadly compares to previous reconstructions, a period of inferred lower salinity within the estuary between 3800–2000 cal yr B.P. is calibrated as brackish and not fresh by the calibration model.  相似文献   

Mapping of the hyporheic zone around a tidal creek using a combination of borehole logging,borehole electrical tomography and cross-creek electrical imaging,New South Wales,Australia     

R. I. Acworth  G. R. Dasey 《Hydrogeology Journal》2003,11(3):368-377

A combination of electrical imaging carried out across a tidal creek and borehole electrical tomography between strings of electrodes installed in bores adjacent to the creek is used to establish the shape of the hyporheic zone beneath a tidal creek in a sand aquifer. The interpretations provided by the data inversions are checked against fluid electrical conductivity (EC) samples collected from bundled piezometers installed in the creek banks and from bulk EC measurements made using induction logs in bores on the creek banks. Extensive seepage into the base of the creek is identified from the electrical image and verified by independent measurements of hydraulic head and fluid EC. The Effective Medium Theory is used to derive values of fluid EC from bulk resistivity measurements obtained from the inversion process. The data show an extensive zone of mixing between seawater and rainwater recharge into the aquifer, with the shape of the hyporheic zone strongly influenced by regional groundwater discharge and the presence of a thin layer of cemented sands at a depth of 10 m. The combined interpretation demonstrates the importance of borehole control in the interpretation of electrical images measured from the surface over complex EC distributions. Electronic Publication  相似文献   

福建沿海、台湾海峡GPS观测分析及地球动力学特征研究   总被引：1，自引：1，他引：1  

丁学仁  林继华  刘序俨  吴绍祖  陈琳 《华南地震》2002,22(2):16-23

利用 3期GPS联测结果所获得的福建沿海地壳水平运动信息 ,采用ITRF94全球框架为基础的GPS测站地壳运动模型及其处理软件 ,对所获得的观测数据进行处理和精度分析。得到福建省高精度的GPS测站大地坐标、边长及其位移矢量 ,其精度达到 1 7×10 - 8。计算了福建地壳运动速率、主应变率 ,东西与南北向线应变率、面应变率、剪应变率、大地转动率和最大剪应变率等值线并给出了它们的分布图象。根据多年形变和现今GPS观测资料 ,分析福建地壳垂直运动与水平运动 ,显示区域应力场优势分布特征。最后 ,对福建沿海及台湾海峡地壳动力学特征作了初步的探讨  相似文献   

Recharge and aquifer response: Northern Guam Lens Aquifer, Guam, Mariana Islands   总被引：1，自引：0，他引：1  

J. M. U. Jocson  J. W. Jenson  D. N. Contractor   《Journal of Hydrology》2002,260(1-4):231-254

The Northern Guam Lens Aquifer is an island karst aquifer in uplifted young, highly conductive limestone. Calculations of recharge based on differences between daily rainfall and daily pan evaporation suggest that the maximum annual mass of water delivered to the freshwater lens is about 67% of mean annual rainfall. Hydrographs of daily well-level responses plotted against daily rainfall indicate that the rate at which water is delivered to the lens is a function of rainfall intensity and the relative saturation of the vadose zone. Together, these variables determine the degree to which stormwater is shunted into fast flow through preferred pathways that bypass the bedrock matrix, rather than percolating slowly through the bedrock matrix.

Data from the 40-year interval from 1956 to 1995 show that some 17% of rainfall on northern Guam arrives in small amounts (<0.6 cm/day). Most of this light rainfall is probably lost to evapotranspiration. At least another 20% of total rainfall on Guam arrives at very high intensities (>5.0 cm/day), which tend to promote fast flow at the expense of percolation. Rapid recovery of the water table from rapid recharge suggests that the lens either takes such recharge into storage very rapidly, discharges it rapidly without taking it into storage, or some combination of both. Significant vadose buffering of recharge to the lens is indicated by the fact that simulations assuming that the recharge from precipitation received in any given month is transmitted to the lens during the same month consistently over-predict observed peak mean monthly water levels and under-predict the minima.  相似文献   

An experimental simulation of a coastal fog-stratus case using COAMPS(tm) model     

Fanyou Kong   《Atmospheric Research》2002,64(1-4)

This paper presents an experimental simulation of a summer season marine fog-stratus case along the west coast of California using the US Navy COAMPS(tm) model. The purpose is to show the potential usefulness of mesoscale models in forecasting this type of marine boundary weather phenomenon. The role of data assimilation and the impacts of solar radiation, microphysics, and vertical resolution in improving the forecasts are examined. The model capability in forecasting the burn-off process over the San Francisco Bay area is also tested with very high horizontal resolution (2-km grid size) using the model's one-way nesting technique. The model demonstrates promising capacity in this case to replicate the temporal and spatial cloud coverage over the San Francisco Bay and surrounding area, shown in satellite imagery, despite a 2-h lag to complete clearing over the bay. This study also suggests that a better microphysics parameterization and proper representation of microphysics in the solar radiation scheme are both important for COAMPS(tm) to produce more realistic simulations and to improve the burn-off forecast.  相似文献   

Inundation Potentials Analysis for Tsao-Ling Landslide Lake Formed by Chi-Chi Earthquake in Taiwan     

Li  Ming-Hsu  Hsu  Ming-Hsi  Hsieh  Lung-Sheng  Teng  Wei-Hsien 《Natural Hazards》2002,25(3):289-303

Without any omen, massive landslides induced by the Chi-Chi earthquake blocked up gorges of Ching-Shui creek, and produced a new landslide lake.Although emergency spillways have been constructed to prevent dam failures,overtopping and possible breaching may still occur due to excessive inflows in raining seasons. As a result, the downstream valleys will have serious inundation and the safety of people and properties will be in immediate danger. The purpose of this work is to simulate and to analyze the inundation potentials downstream of Tsao-Ling landslide lake using a hydrologic/hydraulic approach and GIS (Geographic Information System) technology. Hydrologic analysis is employed to describe regional rainfall-runoff characteristics andto design rainfall/runoff scenarios. One-dimensional dam break flood routings are performed with different return periods of rainfall events and dam failure durations for downstream creeks. The depletion hydrographs of dam break routings are applied into two-dimensional overland flow simulations for downstream lowlands. The results of hydraulic computations are evaluated with GIS maps for inundation potentials analysis, which can be usedto assist the planning of emergency response measures.  相似文献   

CVI评价研究简介与几点建议   总被引：1，自引：0，他引：1  

丘世钧  范小平  萧艳娥 《热带地理》2002,22(3):283-285

海岸脆弱性指数（CVI）评价是最近以来关于未来海平面上升对海岸系统变化的有关可能性的研究方法，它将与海岸变化有关的6个变量以定量研究的形式相联系起来，并在此基础上绘制各岸段的CVI图，CVI可应用于海岸带管理的许多决策方面，作者对未来海平面变化的研究工作提出了几点建议。  相似文献   

闽南沿海地区工程场地的断裂活动性评价   总被引：2，自引：0，他引：2  

黄卿团  丁祥焕 《华南地震》1997,17(3):66-72

根据闽南沿海地区的地质构造特征，对各种工程场地的断裂活动性评价方法进行了探讨，并着重以长乐、厦门、东山３个工程场地为例，对断裂活动性进行分析研究。结果表明，在长乐－诏安断裂带的不同地段，晚更新世以来的断裂具有不同的活动特征。  相似文献   

Results of magnetotelluric and gravimetric measurements in western Nicaragua, Central America   总被引：1，自引：0，他引：1  

Sten-Åke Elming  Thorkild Rasmussen 《Geophysical Journal International》1997,128(3):647-658

Magnetotelluric and gravity data have been collected within a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. 2-D interpretation of the magnetotelluric (MT) data, collected at 13 stations, indicates four regions of high electrical conductivity in addition to the conductive coastal region. Two of these are associated with conducting sediments and pyroclastics in the upper part of the crust. Two other conductive structures have been defined at depth around 20 km and the one best defined is located below the depression. From the distribution of seismic events, volcanic activity in the depression and the similarity in geophysical characteristics with areas such as the Rio Grande Rift, this conductor is interpreted as a melt layer or a complex of magma chambers. Models of the upper lithosphere, constrained by the MT model, vertical electrical sounding (VES) data, seismic data and densities, have been tested using gravity data. A model that passes this test shows a gradual thickening of the crust eastwards from the Pacific coast. An anomaly centred over the depression is interpreted to have its origin in a thinning of the crust. In this model the melt layer is situated on top of the bulge of the lower lithosphere. A change in the composition of the crust, from the Pacific Coastal Plain to the Highland, is indicated from the change in character of the MT response and from the density distribution in the gravity model. This may support the hypothesis that the Pacific region is an accreted terrane. MT and gravity data indicate a depth to a resistive and high-density basement in the depression of ca. 2 km. On the basis of this, the vertical setting in the depression is estimated to be of the order of 2.5 km.  相似文献