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Sinha, Surbhi, and Vinay Kumar Rai. "Topographical Characteristics of Lower Barakar Basin: A Geospatial Approach." National Geographical Journal of India 66, no. 1 (2020): 12–19. http://dx.doi.org/10.48008/ngji.1725.
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The evolution and development of a drainage network largely depends upon the surface topography of a landscape. Even topographic attributes such as overland flow, sub-surface flow, stream flow etc. are highly determined by the relief and slope aspects of the basin area. Topography influences evolution of landforms, soil development, vegetation growth, types of settlement, agricultural pattern etc. So it becomes very important to quantify different topographical parameters so that proper watershed management can be done. This work is an attempt to evaluate existing topography of study area using topographical sheets and SRTM DEM data. For calculation and analysis of data MS Excel is used while Geographical Information System (GIS) is used for mapping purpose. Present work provides better understanding of surface and relief aspects of landforms in Lower Barakar basin.
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Casas, A., S. N. Lane, D. Yu, and G. Benito. "A method for parameterising roughness and topographic sub-grid scale effects in hydraulic modelling from LiDAR data." Hydrology and Earth System Sciences Discussions 7, no. 2 (2010): 2261–99. http://dx.doi.org/10.5194/hessd-7-2261-2010.
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Abstract. High resolution airborne laser data provide new ways to explore the role of topographic complexity in hydraulic modelling parameterisation, taking into account the scale-dependency between roughness and topography. In this paper, a complex topography from LiDAR is processed using a spatially and temporally distributed method at a fine resolution. The surface topographic parameterisation considers the sub-grid LiDAR data points above and below a reference DEM, hereafter named as topographic content. A method for roughness parameterisation is developed based on the topographic content included in the topographic DEM. Five subscale parameterisation schemes are generated (topographic contents at 0, ±5, ±10, ±25 and ±50 cm) and roughness values are calculated using an equation based on the mixing layer theory (Katul et al., 2002), resulting in a co-varied relationship between roughness height and topographic content. Variations in simulated flow across spatial subscales show that the sub grid-scale behaviour of the 2-D model is not well-reflected in the topographic content of the DEM and that subscale parameterisation must be modelled through a spatially distributed roughness parameterisation. Variations in flow predictions are related to variations in the roughness parameter. Flow depth-derived results do not change systematically with variation in roughness height or topographic content but they respond to their interaction. Finally, subscale parameterisation modifies primarily the spatial structure (level of organisation) of simulated 2-D flow linearly with the additional complexity of subscale parameterisation.
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Casas, A., S. N. Lane, D. Yu, and G. Benito. "A method for parameterising roughness and topographic sub-grid scale effects in hydraulic modelling from LiDAR data." Hydrology and Earth System Sciences 14, no. 8 (2010): 1567–79. http://dx.doi.org/10.5194/hess-14-1567-2010.
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Abstract. High resolution airborne laser data provide new ways to explore the role of topographic complexity in hydraulic modelling parameterisation, taking into account the scale-dependency between roughness and topography. In this paper, a complex topography from LiDAR is processed using a spatially and temporally distributed method at a fine resolution. The surface topographic parameterisation considers the sub-grid LiDAR data points above and below a reference DEM, hereafter named as topographic content. A method for roughness parameterisation is developed based on the topographic content included in the topographic DEM. Five subscale parameterisation schemes are generated (topographic contents at 0, ±5, ±10, ±25 and ±50 cm) and roughness values are calculated using an equation based on the mixing layer theory (Katul et al., 2002), resulting in a co-varied relationship between roughness height and topographic content. Variations in simulated flow across spatial subscales show that the sub grid-scale behaviour of the 2-D model is not well-reflected in the topographic content of the DEM and that subscale parameterisation must be modelled through a spatially distributed roughness parameterisation. Variations in flow predictions are related to variations in the roughness parameter. Flow depth-derived results do not change systematically with variation in roughness height or topographic content but they respond to their interaction. Finally, subscale parameterisation modifies primarily the spatial structure (level of organisation) of simulated 2-D flow linearly with the additional complexity of subscale parameterisation.
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Chu, Xuefeng, Xinhua Jia, and Yang Liu. "Quantification of wetting front movement under the influence of surface topography." Soil Research 56, no. 4 (2018): 382. http://dx.doi.org/10.1071/sr17071.
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Soil surface topography affects fundamental hydrologic processes, such as infiltration and soil water percolation. Topographic variations potentially alter both the magnitude and directions of unsaturated flow. The objective of this study is to evaluate the effects of surface topography on wetting front moving patterns under different rainfall and soil conditions through combined experimental and numerical modelling studies. Specifically, laboratory-scale infiltration and unsaturated flow experiments and HYDRUS-2D modelling were conducted for different topographic surfaces, rainfall intensities, and soil types. The simulated and observed wetting front distributions were compared and evaluated. Two different stages were observed: topography-dominated two-dimensional flow and uniform one-dimensional flow. A uniformly distributed wetting front was eventually achieved although soil surfaces had dissimilar topographic characteristics. However, the timing or duration to reach such a uniform flat wetting front varied, mainly depending on surface topography, rainfall characteristics, and soil hydraulic properties. The findings from this study are important to better understand the mechanism of topography-controlled unsaturated flow, wetting front movement, and overland flow generation, and to further improve modelling of soil water flow and transport processes under such complex conditions across different scales.
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Shakespeare, Callum J., Brian K. Arbic, and Andrew McC. Hogg. "The Drag on the Barotropic Tide due to the Generation of Baroclinic Motion." Journal of Physical Oceanography 50, no. 12 (2020): 3467–81. http://dx.doi.org/10.1175/jpo-d-19-0167.1.
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AbstractThe interaction of a barotropic flow with topography generates baroclinic motion that exerts a stress on the barotropic flow. Here, explicit solutions are calculated for the spatial-mean flow (i.e., the barotropic tide) resulting from a spatially uniform but time-varying body force (i.e., astronomical forcing) acting over rough topography. This approach of prescribing the force contrasts with that of previous authors who have prescribed the barotropic flow. It is found that the topographic stress, and thus the impact on the spatial-mean flow, depend on the nature of the baroclinic motion that is generated. Two types of stress are identified: (i) a “wave drag” force associated with propagating wave motion, which extracts energy from the spatial-mean flow, and (ii) a topographic “spring” force associated with standing motion at the seafloor, including bottom-trapped internal tides and propagating low-mode internal tides, which significantly damps the time-mean kinetic energy of the spatial-mean flow but extracts no energy in the time-mean. The topographic spring force is shown to be analogous to the force exerted by a mechanical spring in a forced-dissipative harmonic oscillator. Expressions for the topographic stresses appropriate for implementation as baroclinic drag parameterizations in global models are presented.
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Richter, Nicole, Massimiliano Favalli, Elske de Zeeuw-van Dalfsen, et al. "Lava flow hazard at Fogo Volcano, Cabo Verde, before and after the 2014–2015 eruption." Natural Hazards and Earth System Sciences 16, no. 8 (2016): 1925–51. http://dx.doi.org/10.5194/nhess-16-1925-2016.
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Abstract. Lava flow simulations help to better understand volcanic hazards and may assist emergency preparedness at active volcanoes. We demonstrate that at Fogo Volcano, Cabo Verde, such simulations can explain the 2014–2015 lava flow crisis and therefore provide a valuable base to better prepare for the next inevitable eruption. We conducted topographic mapping in the field and a satellite-based remote sensing analysis. We produced the first topographic model of the 2014–2015 lava flow from combined terrestrial laser scanner (TLS) and photogrammetric data. This high-resolution topographic information facilitates lava flow volume estimates of 43.7 ± 5.2 × 106 m3 from the vertical difference between pre- and posteruptive topographies. Both the pre-eruptive and updated digital elevation models (DEMs) serve as the fundamental input data for lava flow simulations using the well-established DOWNFLOW algorithm. Based on thousands of simulations, we assess the lava flow hazard before and after the 2014–2015 eruption. We find that, although the lava flow hazard has changed significantly, it remains high at the locations of two villages that were destroyed during this eruption. This result is of particular importance as villagers have already started to rebuild the settlements. We also analysed satellite radar imagery acquired by the German TerraSAR-X (TSX) satellite to map lava flow emplacement over time. We obtain the lava flow boundaries every 6 to 11 days during the eruption, which assists the interpretation and evaluation of the lava flow model performance. Our results highlight the fact that lava flow hazards change as a result of modifications of the local topography due to lava flow emplacement. This implies the need for up-to-date topographic information in order to assess lava flow hazards. We also emphasize that areas that were once overrun by lava flows are not necessarily safer, even if local lava flow thicknesses exceed the average lava flow thickness. Our observations will be important for the next eruption of Fogo Volcano and have implications for future lava flow crises and disaster response efforts at basaltic volcanoes elsewhere in the world.
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Kumhálová, J., F. Kumhála, P. Novák, and Š. Matějková. "Airborne laser scanning data as a source of field topographical characteristics ." Plant, Soil and Environment 59, No. 9 (2013): 423–31. http://dx.doi.org/10.17221/188/2013-pse.
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One of the factors frequently affecting yields is topography. Topographic data can be obtained from various sources with different precision. This work evaluates suitability of airborne laser scanning data for use as another source of topographical characteristics creation in a smaller scale in regards to precision agriculture needs. Simple models of elevation, slope and flow accumulation were created and the correlation between yield and topography was determined over a seven-year period in relation to precipitations and temperature. The suitability of airborne laser scanning data was proved with certain limitations. Flow accumulation model derived from original airborne laser scanning data indicated the right trend of flow accumulation but not as clearly compared to other models. In drier years the correlation coefficients between flow accumulation and yield reached up to 60–70%.
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Harmon, Brendan Alexander, Helena Mitasova, Anna Petrasova, and Vaclav Petras. "r.sim.terrain 1.0: a landscape evolution model with dynamic hydrology." Geoscientific Model Development 12, no. 7 (2019): 2837–54. http://dx.doi.org/10.5194/gmd-12-2837-2019.
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Abstract. While there are numerical landscape evolution models that simulate how steady-state flows of water and sediment reshape topography over long periods of time, r.sim.terrain is the first to simulate short-term topographic change for both steady-state and dynamic flow regimes across a range of spatial scales. This free and open-source Geographic Information Systems (GIS)-based topographic evolution model uses empirical models for soil erosion and a physics-based model for shallow overland water flow and soil erosion to compute short-term topographic change. This model uses either a steady-state or unsteady representation of overland flow to simulate how overland sediment mass flows reshape topography for a range of hydrologic soil erosion regimes based on topographic, land cover, soil, and rainfall parameters. As demonstrated by a case study for the Patterson Branch subwatershed on the Fort Bragg military installation in North Carolina, r.sim.terrain simulates the development of fine-scale morphological features including ephemeral gullies, rills, and hillslopes. Applications include land management, erosion control, landscape planning, and landscape restoration.
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SANSÓN, L. ZAVALA, A. GONZÁLEZ-VILLANUEVA, and L. M. FLORES. "Evolution and decay of a rotating flow over random topography." Journal of Fluid Mechanics 642 (December 4, 2009): 159–80. http://dx.doi.org/10.1017/s0022112009991777.
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The evolution and decay of a homogeneous flow over random topography in a rotating system is studied by means of numerical simulations and theoretical considerations. The analysis is based on a quasi-two-dimensional shallow-water approximation, in which the horizontal divergence is explicitly different from zero, and topographic variations are not restricted to be much smaller than the mean depth, as in quasi-geostrophic dynamics. The results are examined by comparing the evolution of a turbulent flow over different random bottom topographies characterized by a specific horizontal scale, or equivalently, a given mean slope. As in two-dimensional turbulence, the energy of the flow is transferred towards larger scales of motion; after some rotation periods, however, the process is halted as the flow pattern becomes aligned along the topographic contours with shallow water to the right. The quasi-steady state reached by the flow is characterized by a nearly linear relationship between potential vorticity and transport function in most parts of the domain, which is justified in terms of minimum-enstrophy arguments. It is found that global energy decays faster for topographies with shorter horizontal length scales due to more effective viscous dissipation. In addition, some comparisons between simulations based on the shallow-water and quasi-geostrophic formulations are carried out. The role of solid boundaries is also examined: it is shown that vorticity production at no-slip walls contributes for a slight disorganization of the flow.
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Constantinou, Navid C. "A Barotropic Model of Eddy Saturation." Journal of Physical Oceanography 48, no. 2 (2018): 397–411. http://dx.doi.org/10.1175/jpo-d-17-0182.1.
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AbstractEddy saturation refers to a regime in which the total volume transport of an oceanic current is insensitive to the wind stress strength. Baroclinicity is currently believed to be the key to the development of an eddy-saturated state. In this paper, it is shown that eddy saturation can also occur in a purely barotropic flow over topography, without baroclinicity. Thus, eddy saturation is a fundamental property of barotropic dynamics above topography. It is demonstrated that the main factor controlling the appearance or not of eddy-saturated states in the barotropic setting is the structure of geostrophic contours, that is, the contours of f/H (the ratio of the Coriolis parameter to the ocean’s depth). Eddy-saturated states occur when the geostrophic contours are open, that is, when the geostrophic contours span the whole zonal extent of the domain. This minimal requirement for eddy-saturated states is demonstrated using numerical integrations of a single-layer quasigeostrophic flow over two different topographies characterized by either open or closed geostrophic contours with parameter values loosely inspired by the Southern Ocean. In this setting, transient eddies are produced through a barotropic–topographic instability that occurs because of the interaction of the large-scale zonal flow with the topography. By studying this barotropic–topographic instability insight is gained on how eddy-saturated states are established.
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Kim, Namgyun, and Byonghee Jun. "Comparative Analysis of Debris Flow Numerical Simulation Based on the Difference between the Resolution of Topographic Information and Grid Size." Journal of the Korean Society of Hazard Mitigation 23, no. 2 (2023): 41–50. http://dx.doi.org/10.9798/kosham.2023.23.2.41.
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In this study, a comparative analysis was conducted for the debris flow that occurred in Gokseong-gun, Jeollanam-do, in August 2020, using the difference between the resolution of topographic information and grid size. High-resolution topographic information (0.03 m) was established through photogrammetry. For comparison, the low-resolution topographic information was obtained from the contour lines of the 1:5000 digital map. The topographic information was depicted as a grid, with resolutions of 1, 5, and 10 m, and analyzed by setting the simulation grid size to 1, 5, and 10 m. According to the topographic resolution, no significant difference was obtained in the numerical simulation results, when high-resolution topographic information from UAV photogrammetry was used, and the analysis was similar to the actual debris flow. Additionally, when the size of the analysis grid for the simulation was 10 m, the simulation was very similar to the actual debris-flow situation. For predicting a risk area using a debris-flow model, it is very important to reflect actual information, such as topography, geology, and rainfall; technical parameters, such as the grid size, are also important. Moreover, determining the optimal grid size by considering the conditions of the study area, such as the basin area, is necessary.
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Pegler, Samuel S., Herbert E. Huppert, and Jerome A. Neufeld. "Topographic controls on gravity currents in porous media." Journal of Fluid Mechanics 734 (October 9, 2013): 317–37. http://dx.doi.org/10.1017/jfm.2013.466.
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AbstractWe present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow, motivated in part by the sequestration of carbon dioxide in saline aquifers. We consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the $n\text{th} $ power of the horizontal distance from a line or point source of a constant volumetric flux. In two-dimensional cases with $n\gt 1/ 2$, the current evolves from a self-similar form at early times, when the effects of variations in topography are negligible, towards a late-time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography. For $n\lt 1/ 2$, the transition between these flow regimes is reversed. We compare our theoretical results in the case $n= 1$ with data from a series of laboratory experiments in which viscous glycerine is injected into an inclined Hele-Shaw cell, obtaining good agreement between the theoretical results and the experimental data. In the case of axisymmetric topography, all topographic exponents $n\gt 0$ result in a transition from an early-time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface. We also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions, finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes. Finally, we apply our mathematical solutions to the geophysical setting at the Sleipner field, concluding that topographic influence is unlikely to explain the observed non-axisymmetric flow.
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Zou, Xianjian, Chuanying Wang, Huan Song, Zengqiang Han, Zhimin Ma, and Weinbin Hu. "Applications of ultrasound imaging system for measuring water-sand parameters during sediment transport process in hydraulic model experiments." Journal of Hydroinformatics 20, no. 2 (2017): 410–23. http://dx.doi.org/10.2166/hydro.2017.025.
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Abstract Moving particles and the topographic bed under muddy water or in sediment-laden flow are often clouded by suspended sediments, making it hard to detect or analyze for visualization. This paper concerns applications of ultrasound imaging measurement method for the visual measurement of related water-sand parameters during sediment transport process in hydraulic model experiments. We use a B-mode ultrasound imaging system to measure the related parameters of suspended sediment concentration (SSC), underwater topographic riverbed, flow velocity and sediment incipient motion, conducted at a water channel. A comprehensive measuring system for the visualization of multiple water-sand parameters is established. Results show that the measurement and analysis of SSC and its space distribution, topography bedform, flow velocity and flow field, and sediment incipient velocity can be realized. Ultrasound imaging measurements of SSC and their space distribution can be shown in real time, and also dynamic monitoring and analysis of sediment incipient motion and topography bedform during the sediment transport process. This method realizes the experimental visualization of the topographic bed and sediment-laden flow. Application of an ultrasound imaging measurement system has promoted the development of sediment movement law research and related hydraulic model experiment measurement technique.
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Casassa, G., and H. H. Brecher. "Relief and decay of flow stripes on Byrd Glacier, Antarctica." Annals of Glaciology 17 (1993): 255–61. http://dx.doi.org/10.1017/s0260305500012933.
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Curvilinear flow stripes appear on aerial photographs and satellite imagery of polar ice. On Byrd Glacier, Antarctica, flow stripes are especially prominent and can be detected on AVHRR imagery down to the ice shelf margin. Aerial photographs of Byrd Glacier (Brecher, 1986) are used to determine photogrammetrically the relief associated with flow stripes on two transverse profiles separated by a distance of 65 km. Two kinds of stripes are found, topographic and textural flow stripes. Topographic flow stripes are associated with a ridge-trough topography with double amplitudes of 7 m to 45 m and slopes of 1–7 %. The valleys of the topographic flow stripes appear bright in the photographs and correspond to snow-covered areas, while ridges appear in general as dark stripes that correspond to bare ice areas with abundant crevasses. Textural flow stripes correspond to bands of distinct crevasse pattern which are not associated with topography. The photogrammetric information is correlated with the brightness pattern across flow stripes that appears on Advanced Very High Resolution Radiometer (AVHRR) data. Flow stripes decay rapidly on the AVHRR imagery over the first 40 km downstream from Byrd Glacier and some persist for nearly 400 km to the front of the Ross Ice Shelf. Velocity was measured across a transect on the upstream photogrammetric profile. There are no velocity discontinuities across the boundaries of flow stripes, which shows that lateral shear between flow stripes is not a valid mechanism for explaining their persistence.
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Constantinou, Navid C., and William R. Young. "Beta-plane turbulence above monoscale topography." Journal of Fluid Mechanics 827 (August 24, 2017): 415–47. http://dx.doi.org/10.1017/jfm.2017.482.
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Using a one-layer quasi-geostrophic model, we study the effect of random monoscale topography on forced beta-plane turbulence. The forcing is a uniform steady wind stress that produces both a uniform large-scale zonal flow $U(t)$ and smaller-scale macroturbulence characterized by standing and transient eddies. The large-scale flow $U$ is retarded by a combination of Ekman drag and the domain-averaged topographic form stress produced by the eddies. The topographic form stress typically balances most of the applied wind stress, while the Ekman drag provides all of the energy dissipation required to balance the wind work. A collection of statistically equilibrated numerical solutions delineate the main flow regimes and the dependence of the time average of $U$ on parameters such as the planetary potential vorticity (PV) gradient $\unicode[STIX]{x1D6FD}$ and the statistical properties of the topography. We obtain asymptotic scaling laws for the strength of the large-scale flow $U$ in the limiting cases of weak and strong forcing. If $\unicode[STIX]{x1D6FD}$ is significantly smaller than the topographic PV gradient, the flow consists of stagnant pools attached to pockets of closed geostrophic contours. The stagnant dead zones are bordered by jets and the flow through the domain is concentrated into a narrow channel of open geostrophic contours. In most of the domain, the flow is weak and thus the large-scale flow $U$ is an unoccupied mean. If $\unicode[STIX]{x1D6FD}$ is comparable to, or larger than, the topographic PV gradient, then all geostrophic contours are open and the flow is uniformly distributed throughout the domain. In this open-contour case, there is an ‘eddy saturation’ regime in which $U$ is insensitive to large changes in the wind stress. We show that eddy saturation requires strong transient eddies that act effectively as PV diffusion. This PV diffusion does not alter the kinetic energy of the standing eddies, but it does increase the topographic form stress by enhancing the correlation between the topographic slope and the standing-eddy pressure field. Using bounds based on the energy and enstrophy power integrals, we show that as the strength of the wind stress increases, the flow transitions from a regime in which the form stress balances most of the wind stress to a regime in which the form stress is very small and large transport ensues.
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Merryfield, William J., and Greg Holloway. "Inviscid quasi-geostrophic flow over topography: testing statistical mechanical theory." Journal of Fluid Mechanics 309 (February 25, 1996): 85–91. http://dx.doi.org/10.1017/s0022112096001565.
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Numerical simulations are employed in a detailed test of the statistical mechanical description of topographic turbulence. Predictions of steady flows correlated with topography are given particular attention. Agreement between numerical and statistical mechanical results is demonstrated for a large range of parameter values, and over an ensemble of random choices of topography and initial conditions.
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Davey, M. K., R. G. A. Hurst, and E. R. Johnson. "Topographic eddies in multilayer flow." Dynamics of Atmospheres and Oceans 18, no. 1-2 (1993): 1–27. http://dx.doi.org/10.1016/0377-0265(93)90002-o.
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Ibanez, Ruy, Joseph Kuehl, Kalyan Shrestha, and William Anderson. "Brief communication: A nonlinear self-similar solution to barotropic flow over varying topography." Nonlinear Processes in Geophysics 25, no. 1 (2018): 201–5. http://dx.doi.org/10.5194/npg-25-201-2018.
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Abstract. Beginning from the shallow water equations (SWEs), a nonlinear self-similar analytic solution is derived for barotropic flow over varying topography. We study conditions relevant to the ocean slope where the flow is dominated by Earth's rotation and topography. The solution is found to extend the topographic β-plume solution of Kuehl (2014) in two ways. (1) The solution is valid for intensifying jets. (2) The influence of nonlinear advection is included. The SWEs are scaled to the case of a topographically controlled jet, and then solved by introducing a similarity variable, η = cxnxyny. The nonlinear solution, valid for topographies h = h0 − αxy3, takes the form of the Lambert W-function for pseudo velocity. The linear solution, valid for topographies h = h0 − αxy−γ, takes the form of the error function for transport. Kuehl's results considered the case −1 ≤ γ < 1 which admits expanding jets, while the new result considers the case γ < −1 which admits intensifying jets and a nonlinear case with γ = −3.
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MURAKI, DAVID J. "Large-amplitude topographic waves in 2D stratified flow." Journal of Fluid Mechanics 681 (June 16, 2011): 173–92. http://dx.doi.org/10.1017/jfm.2011.187.
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Our fundamental understanding of steady, stratified flow over two-dimensional (2D) topography rests on the pioneering works of G. Lyra and R. Long. Within linear theory, Lyra established the far-field radiation conditions that determine the downstream pattern of buoyancy waves. Soon after, Long discovered that the steady, nonlinear streamfunction for special cases of stratified, 2D flow could satisfy the same equations as linear theory, subject to an exact topographic boundary condition. Fourier methods are currently used to compute solutions to Long's theory for arbitrary topography in the near-hydrostatic or small-amplitude topographic parameter regimes. It is not generally appreciated however, that these methods encounter difficulties for flows that are both strongly non-hydrostatic and beyond linear amplitudes. By recasting Long's theory into a linear integral equation, this difficulty is shown to be a computational barrier associated with an ill-conditioning of the Fourier method. The problem is overcome through the development of a boundary integral computation which relies on some lesser known solutions from Lyra's original analysis. This method is well-conditioned for strongly non-hydrostatic flows, and is used to extend the exploration of critical overturning flows over Gaussian and bell-shaped ridges. These results indicate that the critical value of the non-dimensional height () asymptotes to a finite value with increasing non-hydrostatic parameter ().
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Ryzhov, E. A., and K. V. Koshel. "Interaction of a monopole vortex with an isolated topographic feature in a three-layer geophysical flow." Nonlinear Processes in Geophysics 20, no. 1 (2013): 107–19. http://dx.doi.org/10.5194/npg-20-107-2013.
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Abstract. In the frame of a three-layer, quasi-geostrophic analytical model of an f-plane geophysical flow, the Lagrangian advection induced by the interaction of a monopole vortex with an isolated topographic feature is addressed. Two different cases when the monopole is located either within the upper or the middle layer are of our interest. In the bottom layer, there is a delta-function topographic feature, which generates a closed recirculation region in its vicinity due to the background flow. This recirculation region extends to the middle and upper layers, and it plays the role of a topographic vortex. The interaction between the monopole and the topographic vortex causes a complex, including chaotic, advection of fluid particles. We show that the model's parameters, namely the monopole and topographic vortices' strengths and initial positions, and the layers' depths and densities, are responsible for the diverse advection patterns. While the patterns are rather complicated, one can single out two major processes, which mostly govern the fluid particle advection. The first one is the variation in time of the system's phase space structure, so that within the closed region of the topographic vortex, there appear periodically unclosed particle pathways by which the particles leave the topographic vortex. The second one is chaotic advection that arises from the nonstationarity of the monopole–topography interaction.
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Bindschadler, Robert, and Hyeungu Choi. "Increased water storage at ice-stream onsets: a critical mechanism?" Journal of Glaciology 53, no. 181 (2007): 163–71. http://dx.doi.org/10.3189/172756507782202793.
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AbstractThe interdependence of rapid ice flow, surface topography and the spatial distribution of subglacial water are examined by linking existing theories. The motivation is to investigate whether the acceleration of an ice-stream tributary contains a positive feedback that encourages the retention of subglacial water that leads to faster flow. Periodically varying surface and bed topographies are related through a linear ice-flow perturbation theory for various values of mean surface slope, perturbation amplitude and basal sliding speeds. The topographic variations lead to a periodic variation in hydraulic potential that is used to infer the tendency for subglacial water to be retained in local hydraulic potential minima. If water retention leads to enhanced basal sliding, a positive feedback loop is closed that could explain the transition from slower tributary flow to faster-streaming flow and the sustained downstream acceleration along the tributary–ice-stream system. A sensitivity study illustrates that the same range of topographic wavelengths most effectively transmitted from the bed to the surface also strongly influences the behavior of subglacial water. A lubrication index is defined to qualitatively measure the heterogeneity of the subglacial hydrologic system. Application of this index to field data shows that the transition from tributary to ice stream closely agrees with the location where subglacial water may be first stored.
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McKenzie, Marion A., Lauren E. Miller, Jacob S. Slawson, Emma J. MacKie, and Shujie Wang. "Differential impact of isolated topographic bumps on ice sheet flow and subglacial processes." Cryosphere 17, no. 6 (2023): 2477–86. http://dx.doi.org/10.5194/tc-17-2477-2023.
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Abstract. Topographic highs (“bumps”) across glaciated landscapes have the potential to temporarily slow ice sheet flow or, conversely, accelerate ice flow through subglacial strain heating and meltwater production. Isolated bumps of variable size across the deglaciated landscape of the Cordilleran Ice Sheet (CIS) of Washington State present an opportunity to study the influence of topographic highs on ice–bed interactions and ice flow organization. This work utilizes semi-automatic mapping techniques of subglacial bedforms to characterize the morphology of streamlined subglacial bedforms including elongation, surface relief, and orientation, all of which provide insight into subglacial processes during post-Last Glacial Maximum deglaciation. We identify a bump-size threshold of several cubic kilometers – around 4.5 km3 – in which bumps larger than this size will consistently and significantly disrupt both ice flow organization and subglacial sedimentary processes, which are fundamental to the genesis of streamlined subglacial bedforms. Additionally, sedimentary processes are persistent and well developed downstream of bumps, as reflected by enhanced bedform elongation and reduced surface relief, likely due to increased availability and production of subglacial sediment and meltwater. While isolated topography plays a role in disrupting ice flow, larger bumps have a greater disruption to ice flow organization, while bumps below the identified threshold seem to have little effect on ice and subglacial processes. The variable influence of isolated topographic bumps on ice flow of the CIS has significant implications for outlet glaciers of the Greenland Ice Sheet (GrIS) due to similarities in regional topography, where local bumps are largely unresolved.
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Woods, Andrew W. "The topographic control of planetary-scale flow." Journal of Fluid Mechanics 247 (February 1993): 603–21. http://dx.doi.org/10.1017/s0022112093000588.
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We develop a theory to describe the topographic control of planetary-scale flows resulting from the variation of the Earth's rotation with latitude. We show that on passing over topography, an inertial, zonal current on an equatorial β-plane may pass through a control at which the flow changes from a subcritical to a supercritical solution branch. Downstream of this control, a transition back to the subcritical solution branch may occur, for example, by the generation of planetary eddies or radiating Rossby waves. We calculate the energy dissipated across such a transition and discuss the relevance of this theory for a number of atmospheric and oceanic phenomena. We also show that this phenomenon is analogous to the hydraulic control of a non-rotating, stratified flow passing through a channel of variable width.
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Chen, Chien-Yuan, Ho-Wen Chen, and Zhao-Jun Chen. "Determination of Topographic Factors to Initiate Debris Flow Using Statistical Analysis." International Journal of Machine Learning and Computing 4, no. 6 (2014): 547–52. http://dx.doi.org/10.7763/ijmlc.2014.v6.471.
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Casassa, G., and H. H. Brecher. "Relief and decay of flow stripes on Byrd Glacier, Antarctica." Annals of Glaciology 17 (1993): 255–61. http://dx.doi.org/10.3189/s0260305500012933.
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Curvilinear flow stripes appear on aerial photographs and satellite imagery of polar ice. On Byrd Glacier, Antarctica, flow stripes are especially prominent and can be detected on AVHRR imagery down to the ice shelf margin.Aerial photographs of Byrd Glacier (Brecher, 1986) are used to determine photogrammetrically the relief associated with flow stripes on two transverse profiles separated by a distance of 65 km. Two kinds of stripes are found, topographic and textural flow stripes. Topographic flow stripes are associated with a ridge-trough topography with double amplitudes of 7 m to 45 m and slopes of 1–7 %. The valleys of the topographic flow stripes appear bright in the photographs and correspond to snow-covered areas, while ridges appear in general as dark stripes that correspond to bare ice areas with abundant crevasses. Textural flow stripes correspond to bands of distinct crevasse pattern which are not associated with topography.The photogrammetric information is correlated with the brightness pattern across flow stripes that appears on Advanced Very High Resolution Radiometer (AVHRR) data. Flow stripes decay rapidly on the AVHRR imagery over the first 40 km downstream from Byrd Glacier and some persist for nearly 400 km to the front of the Ross Ice Shelf.Velocity was measured across a transect on the upstream photogrammetric profile. There are no velocity discontinuities across the boundaries of flow stripes, which shows that lateral shear between flow stripes is not a valid mechanism for explaining their persistence.
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Smith, R. S., R. D. Moore, M. Weiler, and G. Jost. "Controls on groundwater response and runoff source area dynamics in a snowmelt-dominated montane catchment." Hydrology and Earth System Sciences Discussions 10, no. 2 (2013): 2549–600. http://dx.doi.org/10.5194/hessd-10-2549-2013.
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Abstract. The role of spatial variability in water inputs on runoff source area dynamics has generally not received as much research attention as topography and soils; however, the influence of topography and forest cover on snow surface energy exchanges can result in asynchronous snowmelt throughout a catchment complicating the space-time patterns of runoff generation. This study investigates temporal variation in the relative importance of spatial controls on the occurrence, timing, and persistence of shallow groundwater response utilizing a highly distributed monitoring network in a snowmelt-dominated montane catchment in western Canada. The study findings indicate that deep soil hydraulic conductivity is a first-order control on the distribution of sites that generate shallow groundwater response versus sites that experience only deep percolation. Upslope contributing area and slope gradient are first-order controls on the persistence of groundwater response during peak flow, recession flow, and low flow periods. Runoff source areas expand and contract throughout these periods according to an interplay between catchment wetness and the spatial patterns of topographic convergence. However, controls on the differential timing, intensity, and quantity of snowmelt and controls on vertical versus lateral flux partitioning in the soil overwhelm the influence of topographic convergence on runoff source area dynamics during early spring freshet periods. The study findings suggest that various topographic indices and topography-based rainfall runoff models are not necessarily applicable to modelling snowmelt runoff source area dynamics during all streamflow periods for snowmelt-dominated montane catchments.
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Zavala Sansón, Luis. "Nonlinear and time-dependent equivalent-barotropic flows." Journal of Fluid Mechanics 871 (May 30, 2019): 925–51. http://dx.doi.org/10.1017/jfm.2019.354.
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Some oceanic and atmospheric flows may be modelled as equivalent-barotropic systems, in which the horizontal fluid velocity varies in magnitude at different vertical levels while keeping the same direction. The governing equations at a specific level are identical to those of a homogeneous flow over an equivalent depth, determined by a pre-defined vertical structure. The idea was proposed by Charney (J. Met., vol. 6 (6), 1949, pp. 371–385) for modelling a barotropic atmosphere. More recently, steady, linear formulations have been used to study oceanic flows. In this paper, the nonlinear, time-dependent model with variable topography is examined. To include nonlinear terms, we assume suitable approximations and evaluate the associated error in the dynamical vorticity equation. The model is solved numerically to investigate the equivalent-barotropic dynamics in comparison with a purely barotropic flow. We consider three problems in which the behaviour of homogeneous flows has been well established either experimentally, analytically or observationally in past studies. First, the nonlinear evolution of cyclonic vortices around a topographic seamount is examined. It is found that the vortex drift induced by the mountain is modified according to the vertical structure of the flow. When the vertical structure is abrupt, the model effectively isolates the surface flow from both inviscid and viscous topographic effects (due to the shape of the bottom and Ekman friction, respectively). Second, the wind-driven flow in a closed basin with variable topography is studied (for a flat bottom this is the well-known Stommel problem). For a zonally uniform, negative wind-stress curl in the homogeneous case, a large-scale, anticyclonic gyre is formed and displaced southward due to topographic effects at the western slope of the basin. The flow reaches a steady state due to the balance between topographic,$\unicode[STIX]{x1D6FD}$, wind-stress and bottom friction effects. However, in the equivalent-barotropic simulations with abrupt vertical structure, such an equilibrium cannot be reached because the forcing effects at the surface are enhanced, while bottom friction effects are reduced. As a result, the unsteady flow is decomposed as a set of planetary waves. A third problem consists of performing simulations of the wind-driven flow over realistic bottom topography in the Gulf of Mexico. The formation of the so-called Campeche gyre is explored. It is found that such circulation may be consistent with the equivalent-barotropic dynamics.
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Satomura, Takehiko. "Topographic Disturbance in Viscous Shear Flow." Journal of the Meteorological Society of Japan. Ser. II 64, no. 5 (1986): 665–80. http://dx.doi.org/10.2151/jmsj1965.64.5_665.
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Dewar, William K., and Andrew McC Hogg. "Topographic inviscid dissipation of balanced flow." Ocean Modelling 32, no. 1-2 (2010): 1–13. http://dx.doi.org/10.1016/j.ocemod.2009.03.007.
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Holden, Joseph. "Topographic controls upon soil macropore flow." Earth Surface Processes and Landforms 34, no. 3 (2009): 345–51. http://dx.doi.org/10.1002/esp.1726.
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MERRYFIELD, WILLIAM J., and GREG HOLLOWAY. "Eddy fluxes and topography in stratified quasi-geostrophic models." Journal of Fluid Mechanics 380 (February 10, 1999): 59–80. http://dx.doi.org/10.1017/s0022112098003656.
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Turbulent stratified flow over topography is studied using layered quasi-geostrophic models. Mean flows develop under random forcing, with lower-layer mean stream-function positively correlated with topography. When friction is sufficiently small, upper-layer mean flow is weaker than, but otherwise resembles, lower-layer mean flow. When lower-layer friction is larger, upper-layer mean flow reverses and can exceed lower-layer mean flow in strength. The mean interface between layers is domed over topographic elevations. Eddy fluxes of potential vorticity and layer thickness act in the sense of driving the flow toward higher entropy. Such behaviour contradicts usual eddy parameterizations, to which modifications are suggested.
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Egger, Joseph, and Klaus-Peter Hoinka. "Topographic Instability: Tests." Journal of the Atmospheric Sciences 65, no. 2 (2008): 670–80. http://dx.doi.org/10.1175/2007jas2311.1.
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Abstract Theories of topographic instability predict growth of perturbations of mean flow and wave modes due to their interaction with mountains under favorable conditions. Mountain torques form an important part of this interaction. It has been suggested that topographic instabilities contribute significantly to the subseasonal variability of the atmosphere but observational tests of topographic instability mechanisms have not yet been performed. Greenland is selected as a test bed because of its isolation, simple shape, and appropriate size. The observed flow development during mountain torque events is investigated in terms of a regression analysis. Changes of axial angular momentum and zonal mean wind with respect to the torques are monitored for domains covering Greenland since the acceleration (deceleration) of the regional zonal flow in response to a positive (negative) torque is a key feature of topographic instability. In particular, southern and northern analysis domains are considered separately in order to test “dipole” instability theories in addition to “monopole” situations where the meridional extent of the pressure perturbations is similar to that of Greenland. Moreover, zonal bands are used as analysis domains. It is found that the response of the zonal wind to the torques is quite small and not systematic. There is no evidence of monopole or dipole topographic instability. A less detailed analysis for the Tibetan Plateau leads to the same result. Reasons for these negative outcomes are discussed as are shortcomings of the tests.
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Condie, S. A., and P. B. Rhines. "Topographic Hadley cells." Journal of Fluid Mechanics 280 (December 10, 1994): 349–68. http://dx.doi.org/10.1017/s002211209400296x.
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When a rotating fluid over sloping topography is heated from below and/or cooled from above, horizontal temperature gradients develop which drive convection cells aligned with isobaths. We refer to these cells as topographic Hadley cells. Laboratory experiments reveal that sinking occurs in small cyclonic vortices situated in relatively shallow regions. This is balanced by slower upwelling in adjacent deeper regions. The cross-isobath motions which connect the upwelling and downwelling are accelerated by Coriolis forces, resulting in strong jets which follow isobathic contours. For anticlockwise rotation, the surface jets keep the shallows to their left when looking in the direction of flow, which is opposite to both Kelvin and Rossby wave propagation. The width of the jets scales with the Rossby deformation radius and if this is much less than the width of the slope region then a number of parallel jets form. Motions on the deeper side of the jets where the flow is accelerating are adequately described by linear inviscid theory. However, the strong shears generated by this acceleration lead to baroclinic instability. The resulting cross-stream momentum fluxes broaden and flatten the velocity profile, allowing the flow on the shallow side of the jet to decelerate smoothly before sinking. Topographic Hadley cells are dynamically similar to terrestrial atmospheric Hadley cells and may also be relevant to the zonal jet motions observed on Jupiter and Saturn. It is also suggested that in coastal seas they may represent an important mode of heat (or salt) transfer where surface cooling (or evaporation) drives convection.
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Smith, R. S., R. D. Moore, M. Weiler, and G. Jost. "Spatial controls on groundwater response dynamics in a snowmelt-dominated montane catchment." Hydrology and Earth System Sciences 18, no. 5 (2014): 1835–56. http://dx.doi.org/10.5194/hess-18-1835-2014.
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Abstract. The role of spatial variability in water inputs on runoff dynamics has generally not received as much research attention as topography and soils; however, the influence of topography and forest cover on snow surface energy exchanges can result in asynchronous snowmelt throughout a catchment, complicating the space–time patterns of runoff generation. This study investigates temporal variation in the relative importance of spatial controls on the occurrence, duration, and timing of shallow groundwater response, utilizing a highly distributed monitoring network in a snowmelt-dominated montane catchment in western Canada. The study findings indicate that deep-soil hydraulic conductivity is a first-order control on the spatial distribution of sites that generate shallow groundwater response versus sites that experience only deep percolation. Upslope contributing area and slope gradient are first-order controls on the duration of groundwater response during peak-flow, recession-flow, and low-flow periods. Shallow runoff response areas expand and contract throughout these periods and follow the general spatial patterns of topographic convergence. However, spatial controls on the timing, intensity, and quantity of snowmelt and controls on vertical versus lateral flux partitioning in the soil overwhelm the influence of topographic convergence on runoff patterns during early spring freshet periods. The study findings suggest that various topographic indices and topography-based rainfall runoff models would not likely be good predictors of runoff patterns in snowmelt-dominated montane catchments during early phases of the spring freshet, but would increase in importance as the freshet and post-freshet periods proceed.
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Oh, Young-Hun. "Unmanned Aerial Vehicle-based Digital Topographic Map Production and Flood Flow Analysis." Journal of the Korean Society for Environmental Technology 21, no. 5 (2020): 402–9. http://dx.doi.org/10.26511/jkset.21.5.12.
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Kim, Namgyun, and Byonghee Jun. "Analyzing Debris Flow: Topographical Data and Discharge Rate Study." Journal of the Korean Society of Hazard Mitigation 23, no. 6 (2023): 123–34. http://dx.doi.org/10.9798/kosham.2023.23.6.123.
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This study used an unmanned aerial vehicle (UAV) for aerial photogrammetry at the Seonseri debris flow site in Gokseong-gun, triggered by heavy rainfall in August 2020. Survey data facilitated the generation of orthographic images and high-resolution digital surface mode (DSM). Finite difference method (FDM) numerical analysis simulated debris flow, exploring the impact of discharge rate and topographic data among input variables. Applying the rational formula for determining debris flow discharge rate emphasized the significance of maximum rainfall intensity just before the event, with high estimated values for runoff coefficient and soil concentration. The study highlighted significant variations in debris flow simulation results based on topographical data accuracy, emphasizing the crucial role of precise site-specific topographical data.
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Yin, Yan Li, Bo Xu, Mo Wen Xie, and Xiang Yu Liu. "Study on Quantity Calculation and Influencing Simulation of Debris Flow Based on Three-Dimensional Remote Sensing System." Advanced Materials Research 594-597 (November 2012): 2309–17. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.2309.
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Debris flow is a huge geological disaster，the prediction of the quantity of debris flow is very significant. In this paper, combined with three-dimensional (3D) remote sensing image interpretation, a quantitative method has been proposed to calculate the quantity of debris flow. In the catchment of debris flow, the topography has been divided into zero-time valleys and one-time valleys, and the quantity of debris flow is calculated by two analytical ways of the full amount of portative matter and the amount of portative matter only caused by rainfall. In addition, based on the digital elevation model (DEM) and the amount of portative matter caused by rainfall, the spatial analysis function of the geographic information system (GIS) has been used to calculate the topographic parameters of the cross sectional area and the regional plane area of the catchment of debris flow. Then the relationship of the soil-rock output and the topographic parameters can be discriminated. Furthermore, the influencing range of debris flow can be stimulated. By practices, the analytical results can be used to estimate the dangerous area of potential debris flow.
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Li, Ji, Zhenhua Xu, Zhanjiu Hao, Jia You, Peiwen Zhang, and Baoshu Yin. "Internal Lee Wave Generation from Geostrophic Flow in the Northwestern Pacific Ocean." Journal of Physical Oceanography 53, no. 11 (2023): 2633–50. http://dx.doi.org/10.1175/jpo-d-23-0035.1.
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Abstract Among the global mapping of lee wave generation, a missing piece exists in the northwestern Pacific Ocean (NPO), which features complex topographies and energetic circulations. This study applies Bell’s theory to estimate and map internal lee waves generated by geostrophic flows in the NPO using Mercator Ocean reanalysis data and the full topographic spectra obtained from the latest synthetic bathymetry product. Unlike the dominant contributions from abyssal hills in the Southern Ocean, multiple topographies, including ridges, rises, and continental margins, result in an inhomogeneous lee wave generation with multiple hotspots in the NPO. The generation rate is generally higher in the Philippine basin and lower in the central Pacific seamounts. Over ridges, the rough topography creates a high potential for triggering lee waves. Over rises and continental margins, the stronger currents at the shallow depths are favorable for lee wave generation. In the Kuroshio extension region, the rough topography and strong currents cause the strongest lee wave generation, with an energy flux reaching 100 mW m−2. By mean–eddy decomposition, it is found that the lee wave hotspots contributed by mean flow are concentrated in specific regions, while those by geostrophic eddies are widely distributed. Geostrophic eddies are the primary contributor to lee wave generation, which account for 74.6% of the total energy transferred from geostrophic flow to lee waves. This study also reveals that tides suppress the lee wave generation by 14%, and geostrophic flow can cause an asymmetric generation of internal tides.
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Zhao, Baojun, and Jiaxin Wang. "Forced solitary wave and vorticity with topography effect in quasi-geostrophic modelling." Advances in Mechanical Engineering 15, no. 1 (2023): 168781322211402. http://dx.doi.org/10.1177/16878132221140212.
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A forced KdV equation including the special topography effect is derived to describe nonlinear long wave and solitary eddy based on the quasi-geostrophic potential vorticity model. We obtain the theoretical solution of the equation and the concrete form of stream function through perturbation theory and multi-scale analysis methods. It is found that the joint effect of weak shear basic flow and topography can change the cyclone and anticyclone structure of eddy, and in the meantime topographic structure affects the East-West propagation direction of solitary wave. Finally, according to the interaction between nonlinear long wave and topography by pseudo spectral numerical method, the topographic height is related to the amplitude, wavelength and wave velocity of the excited wave train, and the topography affects not only the spatial structure of wave, but also the amplitude of wave.
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Yin, Zhen, Chen Zuo, Emma J. MacKie, and Jef Caers. "Mapping high-resolution basal topography of West Antarctica from radar data using non-stationary multiple-point geostatistics (MPS-BedMappingV1)." Geoscientific Model Development 15, no. 4 (2022): 1477–97. http://dx.doi.org/10.5194/gmd-15-1477-2022.
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Abstract. The subglacial bed topography is critical for modelling the evolution of Thwaites Glacier in the Amundsen Sea Embayment (ASE), where rapid ice loss threatens the stability of the West Antarctic Ice Sheet. However, mapping of subglacial topography is subject to uncertainties of up to hundreds of metres, primarily due to large gaps of up to tens of kilometres in airborne ice-penetrating radar flight lines. Deterministic interpolation approaches do not reflect such spatial uncertainty. While traditional geostatistical simulations can model such uncertainty, they become difficult to apply because of the significant non-stationary spatial variation of topography over such large surface area. In this study, we develop a non-stationary multiple-point geostatistical (MPS) approach to interpolate large areas with irregular geophysical data and apply it to model the spatial uncertainty of entire ASE basal topography. We collect 166 high-quality topographic training images (TIs) of resolution 500 m to train the gap-filling of radar data gaps, thereby simulating realistic topography maps. The TIs are extensively sampled from deglaciated regions in the Arctic as well as Antarctica. To address the non-stationarity in topographic modelling, we introduce a Bayesian framework that models the posterior distribution of non-stationary TIs assigned to the local line data. Sampling from this distribution then provides candidate training images for local topographic modelling with uncertainty, constrained to radar flight line data. Compared to traditional MPS approaches that do not consider uncertain TI sampling, our approach results in a significant improvement in the topographic modelling quality and efficiency of the simulation algorithm. Finally, we simulate multiple realizations of high-resolution ASE topographic maps. We use the multiple realizations to investigate the impact of basal topography uncertainty on subglacial hydrological flow patterns.
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Dasgupta, Ritabrata, and Nibir Mandal. "Role of double-subduction dynamics in the topographic evolution of the Sunda Plate." Geophysical Journal International 230, no. 1 (2022): 696–713. http://dx.doi.org/10.1093/gji/ggac025.
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SUMMARY The Sunda Plate has shaped itself in a complex tectonic framework, driven by the interactions of multiple subduction zones in its history. Using thermomechanical computational fluid dynamic models we show in this paper how the in-dip double-subduction dynamics has controlled the first-order 3-D topography of this plate, currently bounded by two major N–S trending active trenches: Andaman–Sumatra–Java and Philippines on its western and eastern margins, respectively. We consider six E–W transects to account for an along-trench variation of the subduction parameters: subduction rate (Vc), shallow-depth (200–300 km) slab dip (α) and intertrench distance (ITD, λ) in our 2-D numerical experiments. The deviatoric stress fields and the topographic patterns are found to strongly depend on λ. For large ITDs (λ = 2000–3000 km), the overriding plate develops dominantly tensile stresses in its central zone, forming low topographic elevations. Decreasing λ results in a transition from extensional to contractional deformation, and promotes topographic uplift in the southern part. We explain these effects of λ in terms of the sublithospheric flow vortex patterns produced by the subducting slabs. Large λ (&gt; 2000 km) generates non-interacting flow vortices, located close to the two trenches, leaving the mantle region beneath the overriding plate weakly perturbed. In contrast, small λ results in their strong interaction to produce a single upwelling zone, which facilitates the overriding plate to gain a higher topographic elevation. The stress field predicted from our model is validated with the observed stress patterns. We also interpolate a 3-D topographic surface and vertical uplift rates from the serial model sections, and compare them with the observed surface topography of the Sunda Plate.
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Wang, Shuya, Xu Chen, Jinhu Wang, Qun Li, Jing Meng, and Yang Xu. "Scattering of Low-Mode Internal Tides at a Continental Shelf." Journal of Physical Oceanography 49, no. 2 (2019): 453–68. http://dx.doi.org/10.1175/jpo-d-18-0179.1.
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AbstractA series of laboratory experiments are performed to investigate the scattering of low-mode internal tides at a continental shelf by varying the criticality parameter and normalized topographic height independently. A wide-range synchronized particle image velocimetery (PIV) measures the velocity fields of the internal tides. Beams radiate from both the shelf break and the bottom of the slope, indicating that energy transfers from low modes to higher modes, which is verified by the modal decomposition. Energy is also transferred to higher harmonics, whose amplitude is less than a quarter of that of the first harmonic. The fraction of energy transmitted onshore and dissipated on the topography is determined by both the criticality parameter and the normalized topographic height, while the fraction of energy reflected offshore is dependent only on the criticality parameter. Mean flow with a shear structure induced by internal tides is observed along the continental slope, with horizontal velocity generally half of the amplitude of the incident waves. A net onshore transport along the slope is caused by the onshore current with larger thickness. The strength of the mean flow is dependent on both the criticality parameter and the normalized topographic height, and a linear relationship between the energy of the mean flow and the vertical shear of internal tides is revealed.
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Zhao, Jiajun, Likun Zhang, and Harry L. Swinney. "Topographic height dependence of internal wave generation by tidal flow over random topography." Geophysical Research Letters 42, no. 19 (2015): 8081–87. http://dx.doi.org/10.1002/2015gl065650.
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Foresti, L., M. Kanevski, and A. Pozdnoukhov. "Data-driven exploration of orographic enhancement of precipitation." Advances in Science and Research 6, no. 1 (2011): 129–35. http://dx.doi.org/10.5194/asr-6-129-2011.
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Abstract. This study presents a methodology to analyse orographic enhancement of precipitation using sequences of radar images and a digital elevation model. Image processing techniques are applied to extract precipitation cells from radar imagery. DEM is used to derive the topographic indices potentially relevant to orographic precipitation enhancement at different spatial scales, e.g. terrain convexity and slope exposure to mesoscale flows. Two recently developed machine learning algorithms are then used to analyse the relationship between the repeatability of precipitation patterns and the underlying topography. Spectral clustering is first used to characterize stratification of the precipitation cells according to different mesoscale flows and exposure to the crest of the Alps. At a second step, support vector machine classifiers are applied to build a computational model which discriminates persistent precipitation cells from all the others (not showing a relationship to topography) in the space of topographic conditioning factors. Upwind slopes and hill tops were found to be the topographic features leading to precipitation repeatability and persistence. Maps of orographic enhancement susceptibility can be computed for a given flow, topography and forecasted smooth precipitation fields and used to improve nowcasting models or correct windward and leeward biases in numerical weather prediction models.
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Kozłowski, Michał, and Jolanta Komisarek. "Influence of terrain attributes on organic carbon stocks distribution in soil toposequences of central Poland." Soil Science Annual 69, no. 4 (2018): 215–22. http://dx.doi.org/10.2478/ssa-2018-0022.
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Abstract The paper presents the results of research on the relationship between topography of undulated morainic plateau of postglacial landscape and distribution of organic carbon stocks in soil toposequences. The mean value of the soil organic carbon stocks (SOCS) for Retisols/Luvisols (RT/LV) was statistically lower than for the Phaeozems/Gleysols (PH/GL) but for RT/LV a higher variation of SOCS in comparison to PH/GL was observed. On the basis of Pearson correlation coefficient, the cartographic depth to water (DTW), the topographic wetness index (TWI) and the saga wetness index (SWI) were the most strongly correlated with the SOCS from among 13 analysed topographic attributes. In addition, the DTW was more correlated with SOCS than other topographic variables. Moreover, the DTW based on the channel networks with 2 ha flow initiation thresholds better correlate with SOCS than DTW obtained on the basis of channel networks with 1 ha and 4 ha flow initiation thresholds. Using Stepwise multiple regression analysis (SMLR), we concluded that the topographic attributes controlling the soil water content and slope shape had most impact on SOCS of the undulated morainic plateau of agricultural ecosystem. In this landform, where the RT/LV and PH/GL soil sequences dominate, the SOCS can be estimated by the DTW, TWI and GC (general curvature) with an estimation error of 0.21 kg m−2. In view of the increasing availability of LiDAR data and power of GIS tools, the use of topographic metrics to assess spatial variability of soil properties will play an increasingly important role in the estimation of soil properties.
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Spall, Michael A., and Joseph Pedlosky. "Shelf–Open Ocean Exchange Forced by Wind Jets." Journal of Physical Oceanography 48, no. 1 (2018): 163–74. http://dx.doi.org/10.1175/jpo-d-17-0161.1.
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AbstractThe general problem of exchange from a shallow shelf across sharp topography to the deep ocean forced by narrow, cross-shelf wind jets is studied using quasigeostrophic theory and an idealized primitive equation numerical model. Interest is motivated by katabatic winds that emanate from narrow fjords in southeast Greenland, although similar topographically constrained wind jets are found throughout the world’s oceans. Because there is no net vorticity input by the wind, the circulation is largely confined to the region near the forcing. Circulation over the shelf is limited by bottom friction for weakly stratified flows, but stratification allows for much stronger upper-layer flows that are regulated by weak coupling to the lower layer. Over the sloping topography, the topographic beta effect limits the deep flow, while, for sufficient stratification, the upper-layer flow can cross the topography to connect the shelf to the open ocean. This can be an effective transport mechanism even for short, strong wind events because damping of the upper-layer flow is weak. A variety of transients are generated for an abrupt onset of winds, including short topography Rossby waves, long topographic Rossby waves, and inertial waves. Using parameters representative of southeast Greenland, katabatic wind events will force an offshore transport of O(0.4) Sv (1 Sv ≡ 106 m3 s−1) that, when considered for 2 days, will result in an offshore flux of O(5 × 1010) m3.
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Legg, Sonya, and Jody Klymak. "Internal Hydraulic Jumps and Overturning Generated by Tidal Flow over a Tall Steep Ridge." Journal of Physical Oceanography 38, no. 9 (2008): 1949–64. http://dx.doi.org/10.1175/2008jpo3777.1.
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Abstract Recent observations from the Hawaiian Ridge indicate episodes of overturning and strong dissipation coupled with the tidal cycle near the top of the ridge. Simulations with realistic topography and stratification suggest that this overturning has its origins in transient internal hydraulic jumps that occur below the shelf break at maximum ebb tide, and then propagate up the slope as internal bores when the flow reverses. A series of numerical simulations explores the parameter space of topographic slope, barotropic velocity, stratification, and forcing frequency to identify the parameter regime in which these internal jumps are possible. Theoretical analysis predicts that the tidally driven jumps may occur when the vertical tidal excursion is large, which is shown to imply steep topographic slopes, such that dh/dxN/ω &gt; 1. The vertical length scale of the jumps is predicted to depend on the flow speed such that the jump Froude number is of order unity. The numerical results agree with the theoretical predictions, with finite-amplitude internal hydraulic jumps and overturning forming during strong offslope tidal flow over steep slopes. These results suggest that internal hydraulic jumps may be an important mechanism for local tidally generated mixing at tall steep topography.
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Hergarten, S., and J. Robl. "Modelling rapid mass movements using the shallow water equations in Cartesian coordinates." Natural Hazards and Earth System Sciences 15, no. 3 (2015): 671–85. http://dx.doi.org/10.5194/nhess-15-671-2015.
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Abstract. We propose a new method to model rapid mass movements on complex topography using the shallow water equations in Cartesian coordinates. These equations are the widely used standard approximation for the flow of water in rivers and shallow lakes, but the main prerequisite for their application – an almost horizontal fluid table – is in general not satisfied for avalanches and debris flows in steep terrain. Therefore, we have developed appropriate correction terms for large topographic gradients. In this study we present the mathematical formulation of these correction terms and their implementation in the open-source flow solver GERRIS. This novel approach is evaluated by simulating avalanches on synthetic and finally natural topographies and the widely used Voellmy flow resistance law. Testing the results against analytical solutions and the proprietary avalanche model RAMMS, we found a very good agreement. As the GERRIS flow solver is freely available and open source, it can be easily extended by additional fluid models or source areas, making this model suitable for simulating several types of rapid mass movements. It therefore provides a valuable tool for assisting regional-scale natural hazard studies.
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Clapuyt, François, Veerle Vanacker, Fritz Schlunegger, and Kristof Van Oost. "Unravelling earth flow dynamics with 3-D time series derived from UAV-SfM models." Earth Surface Dynamics 5, no. 4 (2017): 791–806. http://dx.doi.org/10.5194/esurf-5-791-2017.
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Abstract. Accurately assessing geo-hazards and quantifying landslide risks in mountainous environments are gaining importance in the context of the ongoing global warming. For an in-depth understanding of slope failure mechanisms, accurate monitoring of the mass movement topography at high spatial and temporal resolutions remains essential. The choice of the acquisition framework for high-resolution topographic reconstructions will mainly result from the trade-off between the spatial resolution needed and the extent of the study area. Recent advances in the development of unmanned aerial vehicle (UAV)-based image acquisition combined with the structure-from-motion (SfM) algorithm for three-dimensional (3-D) reconstruction make the UAV-SfM framework a competitive alternative to other high-resolution topographic techniques. In this study, we aim at gaining in-depth knowledge of the Schimbrig earthflow located in the foothills of the Central Swiss Alps by monitoring ground surface displacements at very high spatial and temporal resolution using the efficiency of the UAV-SfM framework. We produced distinct topographic datasets for three acquisition dates between 2013 and 2015 in order to conduct a comprehensive 3-D analysis of the landslide. Therefore, we computed (1) the sediment budget of the hillslope, and (2) the horizontal and (3) the three-dimensional surface displacements. The multitemporal UAV-SfM based topographic reconstructions allowed us to quantify rates of sediment redistribution and surface movements. Our data show that the Schimbrig earthflow is very active, with mean annual horizontal displacement ranging between 6 and 9 m. Combination and careful interpretation of high-resolution topographic analyses reveal the internal mechanisms of the earthflow and its complex rotational structure. In addition to variation in horizontal surface movements through time, we interestingly showed that the configuration of nested rotational units changes through time. Although there are major changes in the internal structure of the earthflow in the 2013–2015 period, the sediment budget of the drainage basin is nearly in equilibrium. As a consequence, our data show that the time lag between sediment mobilization by landslides and enhanced sediment fluxes in the river network can be considerable.
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KLYMAK, JODY M., SONYA M. LEGG, and ROBERT PINKEL. "High-mode stationary waves in stratified flow over large obstacles." Journal of Fluid Mechanics 644 (February 10, 2010): 321–36. http://dx.doi.org/10.1017/s0022112009992503.
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Simulations of steady two-dimensional stratified flow over an isolated obstacle are presented where the obstacle is tall enough so that the topographic Froude number, Nhm/Uo ≫ 1. N is the buoyancy frequency, hm the height of the topography from the channel floor and Uo the flow speed infinitely far from the obstacle. As for moderate Nhm/Uo (~1), a columnar response propagates far up- and downstream, and an arrested lee wave forms at the topography. Upstream, most of the water beneath the crest is blocked, while the moving layer above the crest has a mean velocity Um = UoH/(H−hm). The vertical wavelength implied by this velocity scale, λo = 2πUm/N, predicts dominant vertical scales in the flow. Upstream of the crest there is an accelerated region of fluid approximately λo thick, above which there is a weakly oscillatory flow. Downstream the accelerated region is thicker and has less intense velocities. Similarly, the upstream lift of isopycnals is greatest in the first wavelength near the crest, and weaker above and below. Form drag on the obstacle is dominated by the blocked response, and not on the details of the lee wave, unlike flows with moderate Nhm/Uo.Directly downstream, the lee wave that forms has a vertical wavelength given by λo, except for the deepest lobe which tends to be thicker. This wavelength is small relative to the fluid depth and topographic height, and has a horizontal phase speed cpx = −Um, corresponding to an arrested lee wave. When considering the spin-up to steady state, the speed of vertical propagation scales with the vertical component of group velocity cgz = αUm, where α is the aspect ratio of the topography. This implies a time scale = tNα/2π for the growth of the lee waves, and that steady state is attained more rapidly with steep topography than shallow, in contrast with linear theory, which does not depend on the aspect ratio.