共查询到20条相似文献，搜索用时 15 毫秒
1.
Joseph Silk 《地球物理与天体物理流体动力学》2013,107(1):255-256
Abstract The thermally forced circulation of a stably stratified atmosphere in a valley is studied by aid of a simple numerical model. The model is based on the Boussinesq-equations for shallow convection. A diabatic heating is prescribed at slopes of the valley. To better understand the model's response to this heating the linearized basic equations are solved analytically and numerically for cases with highly idealized orography. The most conspicuous features of observed valley wind systems are represented in these solutions. Next, numerical experiments with more complicated orography are described. The influence of the nonlinear terms and of the dissipative terms is considered. Various shapes of the valley and different localities of the heating are prescribed. It turns out that most of the computed features can be understood on the basis of the linear theory. 相似文献
2.
Abstract This is a study of the influence of bottom topography of an ocean basin on the wind‐driven, barotropic ocean circulation. A detailed investigation is made of the role of vorticity transfer to the ocean bottom in the presence of varying topography. It is shown that the wind‐driven gyre over the topography of the North Atlantic has a transport in the western part of the basin only half of that obtained in an ocean of constant depth. 相似文献
3.
Abstract In this unsteady barotropic model of the circulation over an oceanic continental shelf and shelf break, account is taken of variations in the surface wind stress along the coast. It is found that the position of maximum onshore flow is very sensitive to the alongshore variation of the wind stress, and that the longshore current becomes more influenced by the shelf break as the wind stress decreases. The relation between the shelf break secondary upwelling and the surface wind stress is investigated. The secondary upwelling is greatest when the wind is increasing most rapidly. 相似文献
4.
Abstract A nonlinear Stommel model of the ocean circulation on the beta plane, driven by a time periodic wind stress, is investigated in order to study symmetry properties of the observed time-mean ocean gyres. Due to the presence of vorticity advection terms the model will have a steady or rectified response to fluctuating wind fields. In this paper a small inverse Ekman number, “the small beta regime”, is considered. It is demonstrated that for this case all qualitative features of the residual circulation, obtained numerically by Veronis (1970). are reproduced in an analytical way. They include the dipole character of the gyre, its maximum symmetry breaking around the north-south axis for intermediate Reynolds numbers, measuring the ratio of vorticity forcing and dissipation, and the maximum residual response for intermediate forcing frequencies. 相似文献
5.
Andrew F. Bennett 《地球物理与天体物理流体动力学》2013,107(1):113-142
AbstractThe flow in a mechanically driven thin barotropic rotating fluid system is analysed. The linear theory of Baker and Robinson (1969) is modified and extended into the non-linear regime.An internal parameter, the “local Rossby number”, is indicative of the onset of nonlinear effects. If this parameter is 0(1) then inertial effects are as important as Coriolis accelerations in the interior of the transport-turning western boundary layer and both of its Ekman layers. The inertial effects in the Ekman layers, ignored in previous explorations of non-linear wind driven oceanic circulation, are retained here and calculated using an approximation of the Oseen type. The circulation problem is reduced to a system of scalar equations in only two independent variables; the system is valid for non-small local Rossby number provided only that the approximate total vorticity is positive.To complete the solution for small Rossby number a boundary condition for the inertially induced transport is needed. It is found by examining the dynamics controlling this additional transport from the western boundary layer as the transport recirculates through the rest of the ocean basin. The strong constraint of total recirculation within the western boundary layer (zero net inertial transport) is derived.The calculated primary inertial effects are in agreement with the observations of the laboratory model of Baker and Robinson (1969).The analysis indicates the extent to which three-dimensional non-linear circulation can be reduced to a two dimensional problem. 相似文献
6.
利用三年夏季系留气艇探测结果,分析了北京夏季夜间低空急流的一般特征.30％的夜间观测记录出现了低空急流.急流平均高度为200 m,其最大频率出现在140 m左右,90％急流出现在320 m以下.W、SW、SE是夜间低空急流的主要风向.不同观测地点低空急流在速度、风向和高度上存在明显差异.城区低空急流高度大部分时间比郊区高.个例分析表明,在夜间稳定边界层条件下,低空急流与局地山谷风环流强弱变化有很好相关.进一步成因分析认为,斜坡地形产生的热成风、山谷风环流可能是北京夏季夜间低空急流形成的主要原因. 相似文献
7.
Abstract Permeability and storage characteristics in the Tertiary limestone system of southern United States have developed progressively but non-uniformly as circulation of water and solution in the limestone have changed during the geologic and hydrologic history. The limestone formations, predominantly of Eocene age and subordinated of Oligocene and Miocene age, are widespread at and beneath the surface. They commonly dip gently seaward and are covered in coastal areas by Miocene to Recent clays and sands. Sinkholes and other karst features are common, but topographic relief is generally not great. Circulation of water under water-table conditions when the limestone was exposed to meteoric weathering, before middle Miocene time, resulted in development of secondary permeability as solution channels in near-surface parts of the limestone, Marine deposition of middle and late Miocene clays and later emergence converted part of the water-table circulation system to the present great artesian system. Later, Pleistocene changes in sea level caused changed in places where water discharged, which in turn caused changes in rates of circulation and changes in rates and positions of solution of limestone. Both present and past circulation of water have contributed to changes in permeability and storage of this limestone system. 相似文献
8.
Abstract Standard hydrological methods have been used to evaluate the water resources of a volcanic area that comprises the Lower Basin of the Rio Grande de San Miguel, El Salvador. The area of investigation included study of approximately 645 square kilometers. The lower San Miguel Basin consists of a faulted valley situated at the base of a series of old and recent volcanoes bounding the valley on the East, a tuff block to the South, and consolidated volcanics (lahars) on the West and North. The valley fill consists of pyroclastics which diminish in particle size with distance from the volcanoes (Lapilli to ash), in the southern portion; however, the pyroclastics may be interbedded with lake deposits. A principal objective of the evaluation was to assess the feasibility of irrigating 10,000 hectares of the valley. Results based upon the period of study suggest that almost half of the annual precipitation infiltrates into the ground. Of this quantity, about one third is accounted for by the existing hydrological balance between recharge and depletion. The remainder moves from the valley to the San Miguel River as ground-water runoff and, if retained, is sufficient in quantity to meet the full anticipated irrigation demand. 相似文献
9.
le Prof. J. TRICART 《水文科学杂志》2013,58(4):75-84
Abstract The rivers Gard, Herault and Vidourle which go down very rapidly from the Cevennes into the Mediterranean sea, between very steep slopes, are particulary able to transport débris as a consequence of their very big floods. Nevertheless, during the floods of the autumn 1958, which were of a bi- or tricentenial frequency, only the loams, clays and sands were able to reach the sea during the flood. Shingle was transported in great quantities but only upon short distances, of no; more than 2 or 3 km. Even in such torrents, the transport of shingle is very long, and the greater part of the shingle actually present in the river bed was swept out from the foot of the slopes during the last cold period of the Quaternary, under periglacial conditions. The construction of a dam, at the Moulin de Bertrand in the Hérault valley, which does not allow the transit of shingle, did not result in the modifications in the conditions of transport of the pebbles downstream: the pebbles which are presently transported do not come from the upper valley, but are reworked from the accumulations built up in the bed before the construction of the dam. 相似文献
10.
William R. Holland 《地球物理与天体物理流体动力学》2013,107(1):187-210
AbstractOne of the central unsolved theoretical problems of the large scale ocean circulation is concerned with explaining the very large transports measured in western boundary currents such as the Gulf Stream and the Kuroshio. The only theory up to now that can explain the size of these transports is that of non-linear recirculation in which the advective terms in the momentum equations became important near the western boundary. In this paper an alternative explanation is suggested. When bottom topography and baroclinic effects are included in a wind-driven ocean model it is shown that the western boundary current can have a transport larger than that predicted from the wind stress distribution even when the nonlinear advective terms are ignored. The explanation lies in the presence of pressure torques associated with bottom topography which can contribute to the vorticity balance in the same sense as the wind stress curl.Three numerical experiments have been carried out to explore the nature of this process using a three dimensional numerical model. The first calculation is done for a baroclinic ocean of constant depth, the second for a homogeneous ocean with an idealized continental slope topography, and the third for a baroclinic ocean with the same continental slope topography. The nature of the vorticity balance and of the circulation around closed paths is examined in each case, and it is shown that bottom pressure torques lead to enhanced transport in the western boundary current only for the baroclinic case with variable depth. 相似文献
11.
Abstract The development of statistical relationships between local hydroclimates and large-scale atmospheric variables enhances the understanding of hydroclimate variability. The rainfall in the study basin (the Upper Chao Phraya River Basin, Thailand) is influenced by the Indian Ocean and tropical Pacific Ocean atmospheric circulation. Using correlation analysis and cross-validated multiple regression, the large-scale atmospheric variables, such as temperature, pressure and wind, over given regions are identified. The forecasting models using atmospheric predictors show the capability of long-lead forecasting. The modified k-nearest neighbour (k-nn) model, which is developed using the identified predictors to forecast rainfall, and evaluated by likelihood function, shows a long-lead forecast of monsoon rainfall at 7–9 months. The decreasing performance in forecasting dry-season rainfall is found for both short and long lead times. The developed model also presents better performance in forecasting pre-monsoon season rainfall in dry years compared to wet years, and vice versa for monsoon season rainfall. Editor Z.W. Kundzewicz Citation Singhrattna, N., Babel, M.S. and Perret, S.R., 2012. Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables. Hydrological Sciences Journal, 57 (1), 26–41. 相似文献
12.
Heinrich Faust 《Pure and Applied Geophysics》1963,55(1):209-216
Zusammenfassung Auswertungen von Raketenmessungen aus den Zeiten der Zirkulationsumstellungen oberhalb 20 km in Frühling und Herbst lassen den Mechanismus dieser Umstellungen erkennen. Sie machen es mit Hilfe der Nullschichtkonzeption möglich, Schemata der allgemeinen Zirkulation der aussertropischen Breiten für die Umstellungszeiten zu gewinnen.
Diese Arbeit wurde unterstützt vom US-Department of the Army, European Research Office, unter Kontrakt Nr. DA-91-591-EUC-2174. 相似文献
Summary Evaluations of wind measurements of the North American Meteorological Rocket Network gave a picture of seasonal variation of the mean winds in stratosphere and mesosphere. The upper part of Fig. 1 refers to the northern stations (Fort Churchill and Fort Greely), the lower part to all others rocket bases. The periods in which the general circulation changes from west to east and from east to west were investigated by half-month means (Figs. 2–4). With the help of the null layer conception — a persistent wind extrem layer reverses the large scale vertical motion — it was possible to derive a scheme of the general circulation of the nontropical latitudes for spring and fall (Figs. 5-a and b).
Diese Arbeit wurde unterstützt vom US-Department of the Army, European Research Office, unter Kontrakt Nr. DA-91-591-EUC-2174. 相似文献
13.
14.
AbstractHydrological alteration within an ice-marginal valley is analysed in relation to flooding by the River Vistula flowing within that valley. Specifically, the analysis covers the period of the last two centuries (up to the present day), making reference to human impacts and natural disasters. Seven topographic maps, as well as digital terrain model (DTM) analysis of the extent of flooded areas are used to evaluate the linkage with historical flood events. Within the ice-marginal valley, flooding processes are found to still play an important role on the floodplain, although human activities have limited these significantly through the construction of embankments. The changing characteristics of floods generated by different mechanisms (e.g. heavy rainfall and ice jams) are also discussed.
Editor D. Koutsoyiannis 相似文献
15.
GREGORY J. McCABE JR 《水文科学杂志》2013,58(6):873-887
Abstract Winter mean 700-hectoPascal (hPa) height anomalies, representing the average atmospheric circulation during the snow season, are compared with annual streamflow measured at 140 streamgauges in the western United States. Correlation and anomaly pattern analyses are used to identify relationships between winter mean atmospheric circulation and temporal and spatial variability in annual streamflow. Results indicate that variability in winter mean 700-Hpa height anomalies accounts for a statistically significant portion of the temporal variability in annual streamflow in the western United States. In general, above-average annual streamflow is associated with negative winter mean 700-Hpa height anomalies over the eastern North Pacific Ocean and/or the western United States. The anomalies produce an anomalous flow of moist air from the eastern North Pacific Ocean into the western United States that increases winter precipitation and snowpack accumulations, and subsequently streamflow. Winter mean 700-hPa height anomalies also account for statistically significant differences in spatial distributions of annual streamflow. As part of this study, winter mean atmospheric circulation patterns for the 40 years analysed were classified into five winter mean 700-hPa height anomaly patterns. These patterns are related to statistically significant and physically meaningful differences in spatial distributions of annual streamflow. 相似文献
16.
Charles T. SNYDER 《水文科学杂志》2013,58(3):53-59
Abstract The Great Basin section of the Basin and Range Physiographic Province of Nevada and adjoining states is a semiarid to arid region that is completely cut off from the sea. Valleys of the Great Basin are partly or completely surrounded by mountains in contrast to the Basin and Range Province of southern Arizona where isolated mountains are completely surrounded by valleys. Valleys completely surrounded by mountains are described as topographically closed whereas valleys that have surface connections with nearby valleys are considered to be topographically open. However, the topographic characteristics of individual valleys are not necessarily indicators of the hydrologic characteristics. The valley fill may be saturated with water to the ground surface or it may be entirely drained, depending upon the position of the controlling outlet. The playa on the valley floor may be dry or wet depending upon the depth to water in the valley. A classification of valleys of the Great Basin is presented, based on the extent to which a valley is isolated and the depth of the water table. The playa—whether it is wet or dry—is used to determine the classification of an individual valley. 相似文献
17.
J.W. Deardorff 《地球物理与天体物理流体动力学》2013,107(3-4):377-410
Abstract The nonlinear equations of motion are integrated numerically in time for a region of x‐y‐z space of volume 3h × h × h, where h turns out to be a height slightly above the level where the wind first attains the geostrophic flow direction. Only the ideal case is treated of a horizontal lower boundary, neutral stability, horizontal homogeneity of all dependent mean variables except the mean pressure, and statistically steady state. The resulting flow patterns are turbulent and the eddies transport required amounts of momentum vertically. Topics which are investigated include the relative directions of stress, wind shear and wind; differences in Ekman wind spirals for the neutral numerical case and a stable atmospheric case; profiles of dimensionless turbulence statistics; effect of allowing the mean density to be either constant or to decrease with height; effect of the wind direction or latitude upon the turbulence intensities; and characteristic structure of the eddies in the planetary boundary layer. 相似文献
18.
Sunamra Das 《地球物理与天体物理流体动力学》2013,107(1-4):49-60
Abstract The initial-value problem of generation of storm surges by any symmetrically distributed and time-periodic surface wind near a circular island with variable topography is solved. The general steady-state motion at any distance is determined, and some of its characteristics are described. Graphical illustrations are provided for a physically plausible wind stress distribution near a conical island. 相似文献
19.
Abstract The source of the world's largest river has fascinated scientists and adventurers for a long time. Extensive studies have been undertaken in the unexplored Llogueta River valley, Cordillera Chila, to identify the main stream of the Amazon River. Analysis of the Lloqueta River network and measurements of its hydrographic and hydrometric characteristics are presented in this study. On the basis of the acquired data, the northern hillside of the Cordillera Chila massif, concretely the basins of four mountainous courses—the Carhuasanta, Apacheta, Ccaccansa and Sillanque rivers—should be regarded as the headwaters territory of the Amazon River. Factors influencing the river system—glaciers and soils—were examined for each catchment. Glacier retreat in the last 50 years has left perennial snowfields only in the highest part of the study area, resulting in modification of the headwater runoff regimes. Preliminary results are afforded by the continual automatic water-level monitoring of the Lloqueta River since June 2008. Our investigations have determined that all types of soil in the area could be classified into two main categories: hydromorphic soils or poorly developed cryic soils. Citation Janský, B., Engel, Z., Kocum, J., ?efrna, L. & ?esák, J. (2011) The Amazon River headstream area in the Cordillera Chila, Peru: hydrographical, hydrological and glaciological conditions. Hydrol. Sci. J. 56(1), 138–151. 相似文献
20.
Dr. Heinrich Faust 《Pure and Applied Geophysics》1960,47(1):183-190
Zusammenfassung Auf der Basis der Nullschichtkonzeption wurde ein Schema der allgemeinen Zirkulation der außertropischen Breiten bis über 60 km Höhe aufgestellt. Die Temperaturmeßergebnisse, die beim Rocket-Grenade-Unternehmen in Fort Churchill, Canada, erzielt wurden, werden diskutiert im Hinblick auf dieses Zirkulationsschema. Sie stehen mit ihm in völliger Übereinstimmung; außerdem zeigen sie, daß die Zirkulation der außertropischen Breiten auch in der Stratosphäre eine thermischindirekte ist, wie das genannte Zirkulationsschema es angibt.
Der Aufsatz enthält einige Ergebnisse, die in einem von US Department of Army, European Research Office, unter Kontrakt Nr. DA-91-591-EUC-1295 (OI-4152-60) unterstützten Forschungsprojekt gewonnen wurden. 相似文献
Summary In a precedent paper (this Review, Vol 44, 257, 1959) was made a report about the three kinds of Null layers which, by means of empirical-statistical and theoretical investigations, have been found in the atmosphere. The Null layer of the first kind (N 1 ), connected with a wind maximum and the Null layer of the second kind (N 2 ), connected with a wind minimum, reverse the large scale vertical movement, but do not change the direction of the wind. In the improper Null layer (N 3 ) connected with a layer of calm, the vertical movement is also zero. There occurs however no reversal of vertical movement, rather a reversal of wind direction.When the positions of the three Null layers in the atmosphere have been determined, a scheme of the general circulation of the extra-tropical latitudes can be set up. The non-gradient movement of mass of the three Null layers as mentioned in the quoted paper is connected with thermally-indirect circulation. An extension of this scheme to include the tropics requires deeper investigation into the role of the extreme layers of wind with thermally-direct circulation. AN 1 lies in the upper troposphere, aN 2 in winter at about a height of 20 km, aN 3 in summer at about a height of 20 km, aN 1 (winter: west wind maximum, summer: east wind maximum) at about a height of 55 km.The results of the measurements of temperature from the Rocket Grenade Experiments (Fort Churchill, Canada), and especially the striking point of intersection of the winter and summer temperature curves at a height of 60 km, have been found to agrees with the derived results of the circulation scheme. Thus it also follows that the extra-tropical circulation in the stratosphere is thermally-indirect.
Der Aufsatz enthält einige Ergebnisse, die in einem von US Department of Army, European Research Office, unter Kontrakt Nr. DA-91-591-EUC-1295 (OI-4152-60) unterstützten Forschungsprojekt gewonnen wurden. 相似文献