The lunar barometric tide in New Zealand     

Hutchings  J. W.  Webber  S. J. 《Pure and Applied Geophysics》1985,123(2):293-304

The lunar barometric tide has been determined with reasonable accuracy, on an annual and seasonal basis, at five stations on the mainland of New Zealand and at three of the outlying islands. The determinations show that in the New Zealand region the lunar tide has a larger amplitude and smaller phase than might have been expected from previously available southern-hemisphere results. In general, the seasonal variation of phase in the New Zealand region conforms to the currently recognised global pattern, with the J-season phase greater than that of the D-season. Similarly, the amplitude variation tends to support the suggestion that, south of latitude 30°S, the D-season amplitude is greater than that of the J-season. Approximate tests are introduced and used to assess the statistical significance of some of the apparent differences in amplitude and phase made evident by the analysis. These assessments indicate that although many of the apparent differences may be attributed to sampling fluctuations, the main regional anomalies in amplitude and phase are likely to be real. It is suggested that these anomalies may indicate a significant regional input of tidal energy to the atmosphere (at the lower boundary) from the Pacific oceanic tide.  相似文献   

Baroclinic energetics and zonal plane distribution of monsoon disturbances     

P. S. Salvekar  S. K. Mishra 《Pure and Applied Geophysics》1985,123(3):448-462

The adiabatic, quasi-geostraphic, 25-layer, numerical, linear model with Ekman boundary layer friction is utilised to perform the baroclinic stability analysis of the mean monsoon zonal wind profile. It is shown thec _i is a function of the resultant wavenumber alone. This relation is able to explain the effects of the lateral walls on the unstable waves.The energetics and zonal plane distribution of the short and long preferred viscous waves are computed. The upward motion of the short wave together with the warm (cold) core lies to the west of the surface trough position above (below) 850 mb. Further, it is shown that the main source of kinetic energy for the wave lies in the middle layer (850–700 mb) which is transported to the lower and upper layers. Computed is found to be in good agreement with observed values.  相似文献   

降雨及地下水对边坡稳定性动态影响的初步研究   总被引：8，自引：0，他引：8  

罗文强  晏同珍 《地质科技情报》1995,14(4):77-81

论述了降雨及地下水对边坡稳定性的动态影响及作用特征。这种影响特征具有典型的周期性和滞后性，通过对坡体地下水位的动态模拟，取得了边坡稳定性随时间而变化的规律认识。  相似文献   

Time effects on dynamic soil properties under random excitation conditions     

F. Amini 《Soil Dynamics and Earthquake Engineering》1995,14(6):439-443

Two types of clayey soils, a kaolinite and a bentonite, were tested using a resonant column apparatus under random excitation conditions. The concept of root mean square (rms) strain was utilized for the purpose of strain calculations during random loading. The conventional estimator of the transfer function was used for random vibration analysis. The effect of confinement duration (at a constant pressure) on dynamic soil properties, namely damping and shear modulus, was evaluated. The results indicate that for both cohesive soils, the effect of time was less pronounced during random vibration than sinusoidal loading at the same rms strain. This effect is however more pronounced when the peak shearing strain of sinusoidal loading is considered. Furthermore, time effects were more pronounced at low strain levels than at high strain levels.  相似文献   

River channel adjustments downstream from channelization works in England and Wales   总被引：1，自引：0，他引：1  

Andrew Brookes 《地球表面变化过程与地形》1987,12(4):337-351

Relatively little attention has been given to river channel adjustments that occur downstream from channelization works. This study is concerned with the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in England and Wales. Channel changes are identified principally by the method of field survey and by reconstructing the original positions of eroded beds and banks. Use is also made of maps, aerial photographs, and engineering drawings of different dates and the technique of space-for-time substitution is applied. Enlargement of channel cross-sections through erosion had occurred downstream from a variety of types, sizes, and dates of channelization works. The maximum increase of channel size was 153 per cent. Out of a total of 14 sites with enlarged channel cross-sections, seven had undergone a change of width only, at a further three width increased rather than depth, and at the remaining four sites depth increases were dominant. These sites all have relatively high stream powers. Factors causing spatial variation of erosion included tree roots locally binding bank sediments and the occurrence of bends. Planform change had taken place at only one site. A further three high stream power sites had downstream reaches incised into bedrock and therefore did not exhibit adjustment. Channel enlargement is explained in terms of increased flood flows downstream from channelization works causing higher stream velocities, which in turn cause erosion, thereby increasing channel width and/or depth. Examination of flow records for 35 stations revealed flood events which would formerly have spread overbank but are now confined by the channelization works and are therefore likely to alter downstream flows. At sites with downstream change it is proposed that the energy of increased flows was sufficient to exceed a threshold required for erosion of perimeter sediments. By contrast the absence of change at a majority of sites in low energy lowland areas could be a reflection of both the incompetence of increased flows to erode and resistance provided by perimeter sediments. Sites with erosion features appear not to have yet attained new equilibrium conditions.  相似文献   

The effect of the Mt St Helens eruption on tropospheric and stratospheric ions   总被引：1，自引：0，他引：1  

Y. Kondo  R. Reiter  H. Jäger  M. Takagi 《Pure and Applied Geophysics》1982,120(1):11-17

Balloon-borne observations of electrical conductivity in the troposphere and stratosphere were performed using conductivity sondes at Garmisch-Partenkirchen, West Germany, from June to November, 1980, after the Mt St Helens eruption. A significant decrease of atmospheric ions in the altitudes from the troposphere to lower stratosphere has been detected until several months after the eruption in comparison with the observational results obtained before the eruption. Simulteneous ruby lidar observation a month after the eruption indicates an increased amount of aerosol at nearly the same altitude as that of conductivity decrease. Several months after the eruption it appears that aerosols detected by lidar and those effective in reducing ion concentration have different profiles.  相似文献   

The main issues affecting coasts of the Indian and western Pacific Oceans: a meta-analysis from Seas at the Millennium     

Sheppard C 《Marine pollution bulletin》2001,42(12):1199-1207

A review of the world oceans in three volumes by 365 scientists, provides scope for several ‘meta-analyses' of the main problems affecting over 100 areas in the year 2000. This article summarises the main issues affecting a sub-set of the reviewed areas, covering Asian, African and Arabian countries dealt with in Volume 2, which included over 50 articles. From all issues raised, assessment is made of the nature of the major ones, including evaluation of reasons why so many of them remain important issues after so much attention to them. These include long standing problems, several problems more newly flagged as becoming particularly important, the issue of global warming and no less than three related issues connected with fishing and over exploitation. One or two issues such as industrial pollution and sewage, previously considered of almost universal concern, almost traditional pollution issues even, continue to feature strongly for some countries, but while these were almost always referred to in Seas chapters, by and large these categories appear not to be the most pressing of issues today, except in localized areas (albeit areas where huge numbers of people live). Perhaps other issues have simply taken over. They are excluded from this article.  相似文献   

西安地区地下水位下降及其环境负效应   总被引：4，自引：0，他引：4  

王慧芳  岳彩琴  石建胜 《水文地质工程地质》2005,32(3):78-80

本文通过西安地区多年地下水位动态资料,分析区域潜水及城郊自备井集中开采区承压水水位持续下降状况,阐述了地下水位持续下降对水环境、农业环境及城市地质环境所产生的负效应。  相似文献   

Relationships between land-use and forced-pool characteristics in the Colorado Front Range     

Jaime R. Goode  Ellen Wohl   《Geomorphology》2007,83(3-4):249

Land use practices in Colorado during the last two centuries altered the supply of sediment and water to many channels in the upper South Platte Basin. As a result of increased supply of sediment and mobility and reduced peak flows, the characteristics of pools associated with channel constrictions, referred to as forced pools, may have been altered. Increased supply of sediment and reduced transport capacity of high flows could lead to aggradation in forced pools. Channel confined by road corridors could lead to high velocities at normal flows, increased energy dissipation from riprap, or even increased pool frequency resulting from failed riprap. To assess potential alterations, four hypotheses were tested: (1) impacted streams will show significantly different mean volume of pools than a control stream; (2) mean volume of pools on streams where land-use activities increased the supply of sediment will be significantly different from streams solely affected by flow regulation; (3) the strongest change in characteristics of pools of impacted streams will be a reduced volume of pools; (4) streams affected by road corridors will show statistically lower spacing of pools than streams unaffected by roads. The downstream spacing and residual volume of twenty consecutive forced pools were surveyed on five streams in the Colorado Front Range that varied from no contemporary impact to multiple historical and contemporary impacts. ANCOVA with stepwise model selection indicated that degree of land-use (categorical), bankfull spacing of pools, upstream riffle slope and expansion ratio were all significant (α = 0.1) predictors of volume of pools (R² = 0.73). Simple linear regression of mean volume of pools and stream specific variables (gradient, drainage area and discharge) and least square means comparison of mean volume of pools indicated a need to standardize volumes of pools by slope and discharge so that the volumes of pools could be compared among different levels of land-use. Significant correlations between drainage area and volume of pools allowed volume of pools to be standardized by drainage area and thereby discharge. This dimensionless variable was also significantly correlated with channel slope, which permitted the construction of a new variable, PV_QS (volume of pools standardized by discharge and slope). Least square means comparison of mean PV_QS revealed that the control reach was significantly different from road-impacted reaches. Mean volume of pools was significantly larger in the control reach compared to all but one road-impacted stream. This was likely a function of higher wood loading in the control reach and the competence of high flows in the road-impacted reach. Streams affected by road corridors did not have significantly different bankfull spacing of pools from streams not impacted by roads. The multiple interactions among control and response variables explored in this study indicate the need to identify the most constrained and sensitive response variables when attempting to assess channel response to land use.  相似文献   

Seismicity, seismic input and site effects in the Sahel—Algiers region (North Algeria)   总被引：2，自引：0，他引：2  

A. Harbi  S. Maouche  F. Vaccari  A. Aoudia  F. Oussadou  G.F. Panza  D. Benouar 《Soil Dynamics and Earthquake Engineering》2007,27(5):427-447

Algiers city is located in a seismogenic zone. To reduce the impact of seismic risk in this Capital city, a realistic modelling of the seismic ground motion (SGM) is conducted by using the hybrid method that combines the finite differences method and the modal summation. For this purpose, a complete database of geological, geophysical and earthquake data is constructed. A critical re-appraisal of the seismicity of the zone [2.25°E–3.50°E, 36.50°N–37.00°N] is performed and an earthquake list, for the period 1359–2002, is compiled. The analysis of existing and newly retrieved macroseismic information allowed the definition of earthquake parameters of macroseismic events for which a degree of reliability is assigned. Geological cross sections have been built up to model the SGM in the city, caused by the 1989 Mont-Chenoua and the 1924 Douéra earthquakes. Synthetic seismograms and response spectral ratio is produced for Algiers, and they show that the soft sediments in Algiers centre are responsible of the noticed amplification of the SGM.  相似文献