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1.
We discuss the form-drag instability for a quasi-geostrophic channel flow. We first study the characteristics of this instability in a barotropic flow, considering in detail the influence of the meridional scale and discussing which structure of the perturbation zonal flow must be chosen in order to describe properly this instability.We then consider a continuous quasi-geostrophic channel model in which the topography enters only through the bottom boundary condition, and we discuss how in this case the effects of the form-drag are felt by the mean zonal flow through the ageostrophic mean meridional circulation. Because the meridional structure of the perturbation zonal flow cannot simply be extended from the barotropic to the continuous case, we show how to modify it properly.We then study the baroclinic model in the particular case of constant (in the vertical) basic-state zonal flow and show how this case closely resembles the barotropic, demonstrating the barotropic nature of the form-drag instability.Symbols t
is the partial derivative with respect tot.
- x
is the partial derivative with respect tox.
- y
is the partial derivative with respect toy.
-
represents the geostrophic stream function.
-
u
is the eastward component of the geostrophic wind.
-
v
is the northward component of the geostrophic wind.
-
u
a
is the eastward component of the ageostrophic wind.
-
v
a
is the northward component of the ageostrophic wind.
-
w
is the vertical component of the wind.
-
f
is the Coriolis parameter=2 sin f
o+y.
-
f
o
is the Coriolis parameter evaluated at mid-latitude.
-
N
is the Brunt-Vaisala frequency.
- [A]
is the zonal (x) average ofA at constantp andy.
- <A>
is the horizontal (x andy) average ofA at constantp 相似文献
2.
Compared performance of a conceptual and a mechanistic hydrologic models of a green roof 总被引：1，自引：0，他引：1
In order to investigate the hydrologic response of a green roof system within the urban environment, a monitoring campaign is carried out at the green roof site of the University of Genova (Italy). Experimental data confirm that the green roof is able to significantly mitigate the generation of runoff with median values of retained volume and peak reduction, respectively, equal to 94 and 98%. A conceptual linear reservoir and a simple mechanistic (Hydrus‐1D) models are implemented to simulate the hydrologic behaviour of the system; each model is calibrated and validated based on experimental data collected at the green roof site. The hydrographs simulated with both hydrologic models reproduce with acceptable matching capabilities the experimental measurements, as confirmed by the Nash‐Sutcliffe Efficiency index generally greater than 0·60. Although the relative percentage differences evaluated for the selected hydrograph variables (the total effluent volume, the peak flow rate and the hydrograph centroid) demonstrate that the mechanistic model is more accurate, prediction errors of the conceptual model are generally limited when compared with the observed hydrologic performance. Results of the present comparison are useful in supporting conceptual model selection in case the hydrologic response is addressed for hydrologic performance assessment. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
Abolfazl Rezaei Mohammad Zare Ezzatollah Raeisi Reza Namdar Ghanbari 《Ground water》2013,51(2):305-312
Kaftar Lake is a high‐altitude fresh water lake located in High Zagros, south of Iran. Despite the high annual evaporation to precipitation ratio in the area, lake water electrical conductivity is usually lower than 1000 µS/cm, this may be due to high seepage from the floor of the lake. Therefore, the hypothesis of possible underground connections between Namdan Basin, where the lake is located, and the surrounding basins with lower elevation (Aspas and Dehbid Basins) was investigated. Hydrogeology, hydrochemistry, and stable isotopes data of the lake and surrounding basins along with the lake water balance study were applied to test the hypothesis. Results indicate that Kaftar Lake has no connection with Aspas Basin in south, but it is hydraulically connected to Dehbid Basin. In Dehbid Basin, “Ghasr_e_Yaghoob spring” (average discharge ?1200 L/s) emerges from a small outcrop (about 0.8 km2) of Daryan limestone Formation, where this outcrop is much smaller than the required recharge area for such average discharge rate. The study shows that this spring is recharged by Kaftar Lake and Namdan Basin aquifer, through Daryan Formation of Gandboee Syncline located to the northern part of the lake. 相似文献
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Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network 总被引：36，自引：0，他引：36
R. Turcotte J. -P. Fortin A. N. Rousseau S. Massicotte J. -P. Villeneuve 《Journal of Hydrology》2001,240(3-4):225-242
Distributed hydrological models require a detailed definition of a watershed's internal drainage structure. The conventional approach to obtain this drainage structure is to use an eight flow direction matrix (D8) which is derived from a raster digital elevation model (DEM). However, this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed. This is largely due to limitations of the D8 approach and the lack of information over flat areas and pits. The D8 approach alone is also unable to differentiate lakes from plain areas.
To avoid these problems a new approach, using a digital river and lake network (DRLN) as input in addition to the DEM, has been developed. This new approach allows for an accurate fit between the DRLN and the modelled drainage structure, which is represented by a flow direction matrix and a modelled watercourse network. More importantly, the identification of lakes within the modelled network is now possible. The proposed approach, which is largely rooted in the D8 approach, uses the DRLN to correct modelled flow directions and network calculations. For DEM cells overlapped by the DRLN, flow directions are determined using DRLN connections only. The flow directions of the other DEM cells are evaluated with the D8 approach which uses a DEM that has been modified as a function of distance to the DRLN.
The proposed approach has been tested on the Chaudière River watershed in southern Québec, Canada. The modelled watershed drainage structure showed a high level of coherence with the DRLN. A comparison between the results obtained with the D8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure. The proposed approach will benefit hydrological models which require data such as a flow direction matrix, a river and lake network and sub-watersheds for drainage structure information. 相似文献
6.
Shogo Kozaki 《Pure and Applied Geophysics》1976,114(6):879-889
Fields due to an electric current source in the atmosphere where the conductivity increases exponentially with altitude have been calculated. Characteristics of the field are described. The current source is assumednot to vary with time.Department of Electronic Engineering, Gumma University. 相似文献
7.
Salihu Mustafa 《Advances in water resources》1984,7(2):81-84
Flow situation into a ditch resulting from an aquifer that is semi-confined and leaky is investigated. Theoretical solution employing Fourier Series is given and then compared with that obtained by the Laplace Transformation. 相似文献
8.
A. P. Jeary 《地震工程与结构动力学》1986,14(5):733-750
Only when the data base is of sufficient quality can a theoretical model of any process be justified. Such a data base has recently been assembled in the field of damping in tall buildings. It is now possible to specify a damping value appropriate to a particular building vibrating at a specified amplitude which is well correlated with values which are measured in practice. The mechanism on which this predictor is based suggests that the predictor will be applicable to other types of structure as well. As yet the data base for these other structures does not exist, but some circumstantial evidence is encouraging. 相似文献
9.
依托四川茂县跃龙门铁路隧道工程,以主线单线隧道与横通道正交结构为研究对象,通过ABAQUS建立有限元分析模型。选取El-Centro地震波数据,通过应用扩展有限元理论,对横通道与主隧道交叉结构在最不利地震条件下的裂损进行研究,并提出减震层结合柔性接头的抗震措施。研究分析得到:减震层结合柔性接头的设置减小并抑制了交叉结构隧道在强震作用下的开裂范围。柔性接头的设置阻止了纵向裂缝的扩展,在交叉口处中部设置环向柔性接头能完全阻止交叉部位拱顶的裂缝生成;在初期支护和二次衬砌之间设置减震层,给予衬砌更大变形空间,使二次衬砌不易受初期支护变形受力影响而开裂。 相似文献
10.
One of the aims of sewer networks is the protection of population against floods and the reduction of pollution rejected to the receiving water during rainy events. To meet these goals, managers have to equip the sewer networks with and to set up real-time control systems. Unfortunately, a component fault (leading to intolerable behaviour of the system) or sensor fault (deteriorating the process view and disturbing the local automatism) makes the sewer network supervision delicate. In order to ensure an adequate flow management during rainy events it is essential to set up procedures capable of detecting and diagnosing these anomalies.
This article introduces a real-time fault detection method, applicable to sewer networks, for the follow-up of rainy events. This method consists in comparing the sensor response with a forecast of this response. This forecast is provided by a model and more precisely by a state estimator: a Kalman filter. This Kalman filter provides not only a flow estimate but also an entity called ‘innovation’. In order to detect abnormal operations within the network, this innovation is analysed with the binary sequential probability ratio test of Wald. Moreover, by crossing available information on several nodes of the network, a diagnosis of the detected anomalies is carried out. This method provided encouraging results during the analysis of several rains, on the sewer network of Seine-Saint-Denis County, France. 相似文献
11.
J. G. Chakravorty 《Pure and Applied Geophysics》1972,95(1):59-66
Summary Small strain theory has been applied to find out the deformation and stresses in the interior of the earth considered as a self-gravitating non-homogeneous isotropic sphere of heterogeneous density distribution. Stresses have been compared at different layers due to different desity distributions. 相似文献
12.
Michael Dentith Randolph J. Enkin William Morris Cameron Adams Barry Bourne 《Geophysical Prospecting》2020,68(1):178-199
As mineral exploration seeks deeper targets, there will be a greater reliance on geophysical data and a better understanding of the geological meaning of the responses will be required, and this must be achieved with less geological control from drilling. Also, exploring based on the mineral system concept requires particular understanding of geophysical responses associated with altered rocks. Where petrophysical datasets of adequate sample size and measurement quality are available, physical properties show complex variations, reflecting the combined effects of various geological processes. Large datasets, analysed as populations, are required to understand the variations. We recommend the display of petrophysical data as frequency histograms because the nature of the data distribution is easily seen with this form of display. A petrophysical dataset commonly contains a combination of overlapping sub-populations, influenced by different geological factors. To understand the geological controls on physical properties in hard rock environments, it is necessary to analyse the petrophysical data not only in terms of the properties of different rock types. It is also necessary to consider the effects of processes such as alteration, weathering, metamorphism and strain, and variables such as porosity and stratigraphy. To address this complexity requires that much more supporting geological information be acquired than in current practice. The widespread availability of field portable instruments means quantitative geochemical and mineralogical data can now be readily acquired, making it unnecessary to rely primarily on categorical rock classification schemes. The petrophysical data can be combined with geochemical, petrological and mineralogical data to derive explanations for observed physical property variations based not only on rigorous rock classification methods, but also in combination with quantitative estimates of alteration and weathering. To understand how geological processes will affect different physical properties, it is useful to define three end-member forms of behaviour. Bulk behaviour depends on the physical properties of the dominant mineral components. Density and, to a lesser extent, seismic velocity show such behaviour. Grain and texture behaviour occur when minor components of the rock are the dominate controls on its physical properties. Grain size and shape control grain properties, and for texture properties the relative positions of these grains are also important. Magnetic and electrical properties behave in this fashion. Thinking in terms of how geological processes change the key characteristics of the major and minor mineralogical components allows the resulting changes in physical properties to be understood and anticipated. 相似文献
13.
B. Yadava 《Pure and Applied Geophysics》1970,78(1):78-85
Summary The transform calculus has been applied to investigate the disturbances in a composite piezoelectric media traversed by a magnetic field. 相似文献
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The existence of a disturbed region in front of a coronal mass ejection (CME) has been proved; its variation with increasing
CME velocity has been investigated. It has been shown that a plasma density discontinuity, which can be interpreted as a shock
wave, is formed in front of the disturbed region at CME velocities that are about or above the local Alfvén velocity. Within
the experimental error, the observed shock-front width is estimated to be about the mean free path for proton-proton collisions
at distances R < 15−20 R
⊙ from the center of the Sun; i.e., the energy dissipation mechanism in the front is conceivably collisional at these distances. 相似文献
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N.H.C. Sparks S. Mann D.A. Bazylinski D.R. Lovley H.W. Jannasch R.B. Frankel 《Earth and Planetary Science Letters》1990,98(1)
Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and57Fe Mo¨ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 × 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of 110 faces which are capped and truncated by 111 end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. 相似文献