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1
Oliver, Thomas S. N., and Toru Tamura. "Sub-centennially resolved behavior of an accreting sandy shoreline over the past ∼ 1000 years." Journal of Sedimentary Research 91, no. 2 (February 28, 2021): 211–18. http://dx.doi.org/10.2110/jsr.2020.074.
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ABSTRACT Coastal ridge plains represent a valuable record of past shoreline deposition. However, there remain questions regarding shoreline behavior on intermediate timescales (sub-centennial), the impact of storms, and process of ridge genesis. We address these questions through high-resolution reconstruction of the sandy-beach progradation at Boydtown Beach in Twofold Bay, southeastern Australia, over the past 1000 years using ground-penetrating radar (GPR) and optically stimulated luminescence (OSL) dating. GPR profiles are dominated by seaward-dipping reflections that result from beach and dune progradation. Prominent reflections with heavy-mineral concentrations are also preserved resulting from storm erosion. OSL ages reveal alternative phases of steady and episodic accretion, rather than a constant progradation. We hypothesize that steady phases may result from moderate storm events where each successive storm only partially erodes the recovery of the previous event. This results in incremental seaward accretion of the active beach. Phases of episodic accretion could be the result of larger storm events or storm clusters when large post-storm recovery rapidly shifts the active shoreline seaward. The two modes of shoreline progradation (steady and episodic) appear broadly associated with a change in ridge-and-swale morphology whereby subdued ridge swale topography is associated with steady or incremental progradation and higher, better-defined ridges with episodic accretion. These results suggest that a single coastal ridge plain experiences variable intermediate-scale shoreline behavior in response to storm events which then lead to multiple modes of ridge genesis.
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Holley, George R., Rinita A. Dalan, and Philip A. Smith. "Investigations in the Cahokia Site Grand Plaza." American Antiquity 58, no. 2 (April 1993): 306–19. http://dx.doi.org/10.2307/281972.
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Research designed to explore the Grand Plaza at the Cahokia Mounds site, the largest Mississippian-period mound center in the eastern United States, documents that plazas may yield significant information regarding Mississippian manipulation of the landscape and the initial growth of mound centers. Probing and excavation within the Grand Plaza revealed that buried ridge-swale topography, identified through an electromagnetic-conductivity survey, was stripped and then filled by the Cahokians. Excavation also corroborated the presence of deep-pit borrows identified by remote sensing. Based on the ceramics recovered from our excavations, we argue that these earth-moving events were initiated prior to the onset of the Mississippian period (ca. A.D. 1000). Reclamation of the borrowed areas resulted in the formation of the mound-plaza configuration early during the Mississippian period.
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Dalan, Rinita A. "Defining archaeological features with electromagnetic surveys at the Cahokia Mounds State Historic Site." GEOPHYSICS 56, no. 8 (August 1991): 1280–87. http://dx.doi.org/10.1190/1.1443150.
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Electromagnetic (EM) surveys have been used at the Cahokia Mounds State Historic Site in southwestern Illinois to locate and define a number of buried archaeological features. Two instruments, Geonics EM31-D and EM38 conductivity meters, were employed to locate portions of a wooden stockade known as the Central Palisade; delineate a number of leveled earthen mounds; and explore a broad, flat area in the central portion of the site known as the Grand Plaza. EM surveys, together with limited excavation, provide a cost effective and nondestructive means of exploring a site as large and complex as Cahokia. Archaeological excavations confirmed that EM surveys were able to locate the Central Palisade, and more importantly, that they provided information on anthropogenically modified terrain within the Grand Plaza. The EM survey documented buried ridge and swale topography and borrow pits within this area. This evidence of landscape modification challenges previous conceptions about the extent of earthmoving at this important Mississippian center and suggests a promising area of application for EM surveys in archaeology.
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Thonon, I., H. Middelkoop, and M. van der Perk. "The influence of floodplain morphology and river works on spatial patterns of overbank deposition." Netherlands Journal of Geosciences - Geologie en Mijnbouw 86, no. 1 (April 2007): 63–75. http://dx.doi.org/10.1017/s0016774600021326.
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AbstractFloodplain topography and related hydraulic patterns of overbank flow constitute a major control on the amounts and patterns of sediment deposition on floodplains. We studied the differences in sediment deposition at two scales along two river branches of the lower River Rhine in the Netherlands: the Waal and IJssel River. Human alterations like levelling and embankment construction have severely impacted the floodplains along the Waal River branch (average discharge: 1500 m3·s‒1), whereas the relatively wide floodplains along the IJssel River (average discharge: 250 m3·s‒1) still exhibit their characteristic ridge-and-swale topography and natural levees. We found that, in general, the amounts of sediment deposited sediment decreases with increasing distance to the sediment source. Clay and organic matter content generally increase with decreasing floodplain elevation. These trends are, however, far less pronounced in the Waal River floodplains than in the IJssel River floodplains. Sediment deposited on the IJssel River floodplains also contains significantly more sand than the sediment deposited on the Waal River floodplains, probably because of the absence of minor embankments along the IJssel River and its higher sinuosity. Furthermore, during inundation the individual Waal River floodplains receive more sediment per unit area than the IJssel River floodplains. At the scale of the river branch, however, the conveyance losses in the Waal River are less than in the IJssel River, because of the larger surface area of the floodplains along the IJssel River relative to its water and sediment discharge during flood events. This discrepancy stresses that both the individual floodplain sections and the total river branch should be taken into account when studying the role of overbank deposition as part of a river’s sediment budget.
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Hargrave, Michael L., Tad Britt, and Matthew D. Reynolds. "Magnetic Evidence of Ridge Construction and Use at Poverty Point." American Antiquity 72, no. 4 (October 2007): 757–70. http://dx.doi.org/10.2307/25470444.
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A magnetic field gradient survey was conducted at Poverty Point to determine if that technique could detect discrete subsurface features and differentiate the ridges and swales in an area that today exhibits very little topographic relief. The survey area (280 m long by 20 to 60 m wide) crossed Ridges 1 through 5 in the southwest portion of the site. The ridges were revealed as variegated bands of positive and negative magnetic anomalies whereas the swales appeared to be relatively homogeneous. Ridge 1, nearest the plaza, is wider and higher but has less of a flank midden than the other ridges. Two roughly circular arrangements of anomalies on Ridge I are potentially important but cannot be reliably interpreted without ground truthing excavations. Future large-area, high-resolution magnetic gradient surveys could dramatically enhance our understanding of this enigmatic site.
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Clark, David B., Deborah A. Clark, Paul M. Rich, Stuart Weiss, and Steven F. Oberbauer. "Landscape-scale evaluation of understory light and canopy structures: methods and application in a neotropical lowland rain forest." Canadian Journal of Forest Research 26, no. 5 (May 1, 1996): 747–57. http://dx.doi.org/10.1139/x26-084.
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Light is a key resource controlling tree regeneration in the understory of closed-canopy old-growth forests. To evaluate the distribution of understory light environments at a landscape scale, we used stratified random sampling in a 500-ha stand of Costa Rican tropical rain forest. Fifteen 100 m long transects were placed using random coordinates within two soil–geomorphology units (flat alluvial terraces and dissected ridge-slope-swale terrain). At 2.5-m intervals we measured canopy height and slope angle, classified topographic position, and took canopy photographs with a fish-eye lens at 1 and 3 m above the ground (and at 0.6 and 5 m height at five stations per transect). Photographs were analyzed for global site factor (GSF), which is analogous to the percentage of full sun radiation reaching a point. Canopy height and GSF at 1 and 3 m above the ground were significantly autocorrelated (Moran's I) at 2.5-m intervals. The autocorrelation rapidly declined at greater intervals, reaching nonsignificance at ca. 20 m. Both canopy height and GSF at 3 m height had a weak tendency for negative autocorrelations at intervals of 25–50 m. Median canopy height (615 stations) was 23 m (range 0–37). Gaps (canopy height ≤2 m, Brokaw 1982) were only 1.5% of sample points. Gaps were more frequent on steep slopes than on terraces, ridgetops, swales, and gentle slopes. Canopy height varied significantly across this topographic gradient. At all four heights (0.6, 1, 3, and 5 m) median GSF was ≤2.4%. GSF values >8% accounted for only 3% of the total sample (N = 1380). GSF was only weakly negatively correlated with canopy height and the relation was not monotonie. Under canopies 13-19 m tall, nearly all GSF values were ≤5%. Higher GSFs were more frequent under both shorter and taller canopies. Given the observed variance in GSF and canopy height, 100–200 points separated by intervals of ≥20 m are necessary to measure the forest-wide means of these variables to ±10%. We discuss implications of these results for current approaches to modeling understory light based on canopy characteristics. We compared the random background of light environments from 1–3 m above the ground at La Selva with those occupied by saplings of pioneer and nonpioneer tree species. The two pioneers (Cecropia spp.) occurred in microsites significantly brighter than random sites, while sapling microsites of all five nonpioneer species were significantly darker than random. Comparing the landscape-scale distribution of key resources with species' actual distributions at similar scales offers a quantitative method for assessing plant life histories within and among forests.
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AlYousif, Ahmad, Arnoldo Valle-Levinson, Peter N. Adams, and Jorge A. Laurel-Castillo. "Tidal and subtidal hydrodynamics over ridge-swale bathymetry." Continental Shelf Research 219 (April 2021): 104392. http://dx.doi.org/10.1016/j.csr.2021.104392.
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Houser, Chris. "Feedback between ridge and swale bathymetry and barrier island storm response and transgression." Geomorphology 173-174 (November 2012): 1–16. http://dx.doi.org/10.1016/j.geomorph.2012.05.021.
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Nadeau, Louis-Philippe, David N. Straub, and David M. Holland. "Comparing Idealized and Complex Topographies in Quasigeostrophic Simulations of an Antarctic Circumpolar Current." Journal of Physical Oceanography 43, no. 8 (August 1, 2013): 1821–37. http://dx.doi.org/10.1175/jpo-d-12-0142.1.
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Abstract The circumpolar transport of a wind-driven quasigeostrophic Antarctic Circumpolar Current is considered. Simple theory suggests transport in a strongly forced regime—the focus of this study—is largely determined by a partitioning of the southward Sverdrup flux into Drake Passage latitudes: some streamlines feed a “basin contribution” to the circumpolar transport and others feed a large-scale recirculation gyre. Simulations assuming an idealized Scotia Ridge topography are considered to test for sensitivity to resolution. Considerable sensitivity to both vertical and horizontal resolution is found, and associated with this is a tight stationary eddy trapped on the western flank of the ridge. That is, this eddy is sensitive to resolution and exerts an influence that acts to reduce the circumpolar transport. Simulations using the Scotia Ridge–like topography are also compared to others using more realistic topography. In the idealized (ridge) topography experiments, there is only a single ridge against which topographic form drag can act to remove eastward momentum from the system; in the complex topography experiments, there are many. It is found that the experiments assuming realistic topography do not develop an analog to the single topographically trapped eddy prevalent in the Scotia Ridge topography simulations. Additionally, circumpolar transport in these simulations agrees better with the theory. Whether this agreement is simply fortuitous, however, is unclear. To address this, a series of simulations assumes topography that varies smoothly between the idealized ridge and realistic configurations.
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Xu, Guo Dong, Zheng Hua Zhou, Jing Shan Bo, and Wei Hua Fang. "Effect of Ridge Topography on Earthquake Ground Motion." Advanced Materials Research 594-597 (November 2012): 1696–701. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.1696.
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The ridge topography can substantially influence seismic ground motion and, in general, causes the amplification of seismic ground motion amplitude at ridges. Fortunately, sets of three-component accelerogram, obtained by the observation arrays for topographic effect at Zigong Xishan, Jiangyou Doutuan and Qingchuan Sanguo from the great Wenchuan earthquake and its aftershocks, provided basic data for analyzing the effect of ridge topography on seismic ground motion. On the base of these acceleration records, peak ground acceleration and response spectrum ratios are calculated, and examined and compared in order to grasp the effect of ridge topography on ground motion. The findings showed that ridge topography has the remarkable effect on seismic ground motion, in which the amplification characteristics varies depending on the shape of ridge topography, and the amplification effect of the horizontal directions are not similar to the vertical direction, and in some periods are even less than 1.0.
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Li, James, Robert Orland, and Tom Hogenbirk. "Environmental road and lot drainage designs: alternatives to the curb-gutter-sewer system." Canadian Journal of Civil Engineering 25, no. 1 (January 1, 1998): 26–39. http://dx.doi.org/10.1139/l97-044.
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Traditionally, road and lot drainage systems have been designed to convey storm runoff away as quickly as possible to reduce localized ponding. This drainage concept, using curb-gutter-sewer systems, has led to downstream flooding, erosion, water-quality degradation, reduced groundwater recharge and stream baseflow, and aquatic habitat destruction. This paper examines the pros and cons of curb-gutter-sewer systems and qualitatively compares various forms of open ditch - swale drainage alternatives with the conventional curb-gutter-sewer drainage system. These open ditch - swale drainage alternatives not only provide drainage functions but also promote infiltration, trap sediments, and reduce flow velocity along the drainage path. Thus, they can reduce erosion, enhance runoff quality, and increase groundwater recharge. However, they usually require a wider right-of-way than the conventional curb-gutter-sewer systems and may not be suitable for sites with steep topography or erosive soils. For sites that are suitable for the application of these alternative drainage systems, their environment functions make them more attractive than the conventional curb-gutter-sewer system.Key words: drainage systems, storm water, curbs, gutters, sewers, ditches, swales.
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Chen, Changheng, and Igor Kamenkovich. "Effects of Topography on Baroclinic Instability." Journal of Physical Oceanography 43, no. 4 (April 1, 2013): 790–804. http://dx.doi.org/10.1175/jpo-d-12-0145.1.
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Abstract The importance of bottom topography in the linear baroclinic instability of zonal flows on the β plane is examined by using analytical calculations and a quasigeostrophic eddy-resolving numerical model. The particular focus is on the effects of a zonal topographic slope, compared with the effects of a meridional slope. A zonal slope always destabilizes background zonal flows that are otherwise stable in the absence of topography regardless of the slope magnitude, whereas the meridional slopes stabilize/destabilize zonal flows only through changing the lower-level background potential vorticity gradient beyond a known critical value. Growth rates, phase speeds, and vertical structure of the growing solutions strongly depend on the slope magnitude. In the numerical simulations configured with an isolated meridional ridge, unstable modes develop on both sides of the ridge and propagate eastward of the ridge, in agreement with analytical results.
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Wilcox, Douglas A., Steve J. Baedke, and Todd A. Thompson. "A Complicated Groundwater Flow System Supporting Ridge-and-Swale Wetlands in a Lake Michigan Strandplain." Wetlands 40, no. 5 (May 8, 2020): 1481–93. http://dx.doi.org/10.1007/s13157-020-01302-8.
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Gushurst, Greg, and Rezene Mahatsente. "Lithospheric Structure of the Central Andes Forearc from Gravity Data Modeling: Implication for Plate Coupling." Lithosphere 2020, no. 1 (August 27, 2020): 1–13. http://dx.doi.org/10.2113/2020/8843640.
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Abstract Geodetic and seismological data indicates that the Central Andes subduction zone is highly coupled. To understand the plate locking mechanism within the Central Andes, we developed 2.5-D gravity models of the lithosphere and assessed the region’s isostatic state. The densities within the gravity models are based on satellite and surface gravity data and constrained by previous tomographic studies. The gravity models indicate a high-density (~2940 kg m-3) forearc structure in the overriding South American continental lithosphere, which is higher than the average density of the continental crust. This structure produces an anomalous pressure (20-40 MPa) on the subducting Nazca plate, contributing to intraplate coupling within the Central Andes. The anomalous lithostatic pressure and buoyancy force may be controlling plate coupling and asperity generation in the Central Andes. The high-density forearc structure could be a batholith or ophiolite emplaced onto the continental crust. The isostatic state of the Central Andes and Nazca plate is assessed based on residual topography (difference between observed and isostatic topography). The West-Central Andes and Nazca ridge have ~0.78 km of residual topography, indicating undercompensation. The crustal thickness beneath the West-Central Andes may not be sufficient to isostatically support the observed topography. This residual topography may be partially supported by small-scale convective cells in the mantle wedge. The residual topography in the Nazca ridge may be attributed to density differences between the subducting Nazca slab and the Nazca ridge. The high density of the subducted Nazca slab has a downward buoyancy force, while the less dense Nazca ridge provides an upward buoyancy force. These two forces may effectively raise the Nazca ridge to its current-day elevation.
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Argyilan, Erin P., Steven L. Forman, John W. Johnston, and Douglas A. Wilcox. "Optically stimulated luminescence dating of late Holocene raised strandplain sequences adjacent to Lakes Michigan and Superior, Upper Peninsula, Michigan, USA." Quaternary Research 63, no. 2 (March 2005): 122–35. http://dx.doi.org/10.1016/j.yqres.2004.12.001.
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This study evaluates the accuracy of optically stimulated luminescence to date well-preserved strandline sequences at Manistique/Thompson bay (Lake Michigan), and Tahquamenon and Grand Traverse Bays (Lake Superior) that span the past ∼4500 yr. The single aliquot regeneration (SAR) method is applied to produce absolute ages for littoral and eolian sediments. SAR ages are compared against AMS and conventional 14C ages on swale organics. Modern littoral and eolian sediments yield SAR ages <100 yr indicating near, if not complete, solar resetting of luminescence prior to deposition. Beach ridges that yield SAR ages <2000 yr show general agreement with corresponding 14C ages on swale organics. Significant variability in 14C ages >2000 cal yr B.P. complicates comparison to SAR ages at all sites. However, a SAR age of 4280 ± 390 yr (UIC913) on ridge77 at Tahquamenon Bay is consistent with regional regression from the high lake level of the Nipissing II phase ca. 4500 cal yr B.P. SAR ages indicate a decrease in ridge formation rate after ∼1500 yr ago, likely reflecting separation of Lake Superior from lakes Huron and Michigan. This study shows that SAR is a credible alternative to 14C methods for dating littoral and eolian landforms in Great Lakes and other coastal strandplains where 14C methods prove problematic.
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Carlson Mazur, Martha L., Douglas A. Wilcox, and Michael J. Wiley. "Hydrogeology and Landform Morphology Affect Plant Communities in a Great Lakes Ridge-and-Swale Wetland Complex." Wetlands 40, no. 6 (June 17, 2020): 2209–24. http://dx.doi.org/10.1007/s13157-020-01312-6.
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Wilcox, Douglas A., Martha L. Carlson Mazur, and Todd A. Thompson. "Groundwater Controls on Wetland Vegetation of a Ridge-and-Swale Chronosequence in a Lake Michigan Embayment." Wetlands 40, no. 6 (August 20, 2020): 2425–42. http://dx.doi.org/10.1007/s13157-020-01336-y.
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KALLIADASIS, SERAFIM, and G. M. HOMSY. "Stability of free-surface thin-film flows over topography." Journal of Fluid Mechanics 448 (November 26, 2001): 387–410. http://dx.doi.org/10.1017/s0022112001006231.
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We consider the stability of the steady free-surface thin-film flows over topography examined in detail by Kalliadasis et al. (2000). For flow over a step-down, their computations revealed that the free surface develops a ridge just before the entrance to the step. Such capillary ridges have also been observed in the contact line motion over a planar substrate, and are a key element of the instability of the driven contact line. In this paper we analyse the linear stability of the ridge with respect to disturbances in the spanwise direction. It is shown that the operator of the linearized system has a continuous spectrum for disturbances with wavenumber less than a critical value above which the spectrum is discrete. Unlike the driven contact line problem where an instability grows into well-defined rivulets, our analysis demonstrates that the ridge is surprisingly stable for a wide range of the pertinent parameters. An energy analysis indicates that the strong stability of the capillary ridge is governed by rearrangement of fluid in the flow direction flowing to the net pressure gradient induced by the topography at small wavenumbers and by surface tension at high wavenumbers.
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Klymak, Jody M., Maarten Buijsman, Sonya Legg, and Robert Pinkel. "Parameterizing Surface and Internal Tide Scattering and Breaking on Supercritical Topography: The One- and Two-Ridge Cases." Journal of Physical Oceanography 43, no. 7 (July 1, 2013): 1380–97. http://dx.doi.org/10.1175/jpo-d-12-061.1.
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Abstract A parameterization is presented for turbulence dissipation due to internal tides generated at and impinging upon topography steep enough to be “supercritical” with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing—either barotropic or baroclinic. Internal modes that are arrested at the crest of the topography are assumed to dissipate, and faster modes assumed to propagate away. The energy flux into each mode is predicted using a knife-edge topography that allows linear numerical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of barotropic and internal tides impinging on an isolated ridge, and for the generation problem on a two-ridge system. The recipe is seen to work well compared to numerical simulations of isolated ridges, so long as the ridge has a slope steeper than twice the critical steepness. For less steeply sloped ridges, near-critical generation becomes more dominant. For the two-ridge case, the recipe works well when compared to numerical model runs with very thin ridges. However, as the ridges are widened, even by a small amount, the recipe does poorly in an unspecified manner because the linear response at high modes becomes compromised as it interacts with the slopes.
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SAPRYKIN, SERGEY, RUDY J. KOOPMANS, and SERAFIM KALLIADASIS. "Free-surface thin-film flows over topography: influence of inertia and viscoelasticity." Journal of Fluid Mechanics 578 (April 26, 2007): 271–93. http://dx.doi.org/10.1017/s0022112007004752.
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We consider viscoelastic flows over topography in the presence of inertia. Such flows are modelled by an integral-boundary-layer approximation of the equations of motion and wall/free-surface boundary conditions. Steady states for flows over a step-down in topography are characterized by a capillary ridge immediately before the entrance to the step. A similar capillary ridge has also been observed for non-inertial Newtonian flows over topography. The height of the ridge is found to be a monotonically decreasing function of the Deborah number. Further, we examine the interaction between capillary ridges and excited non-equilibrium inertia/viscoelasticity-driven solitary pulses. We demonstrate that ridges have a profound influence on the drainage dynamics of such pulses: they accelerate the drainage process so that once the pulses pass the topographical feature they become equilibrium ones and are no longer excited.
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Small, Christopher. "A global analysis of mid-ocean ridge axial topography." Geophysical Journal International 116, no. 1 (January 1994): 64–84. http://dx.doi.org/10.1111/j.1365-246x.1994.tb02128.x.
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Yassin, Mohamed Fathy, T. Takahashi, and S. Kato. "Experimental simulation of wind flow over the ridge topography." Air Quality, Atmosphere & Health 5, no. 3 (September 24, 2010): 293–301. http://dx.doi.org/10.1007/s11869-010-0090-7.
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Musgrave, R. C., R. Pinkel, J. A. MacKinnon, Matthew R. Mazloff, and W. R. Young. "Stratified tidal flow over a tall ridge above and below the turning latitude." Journal of Fluid Mechanics 793 (March 29, 2016): 933–57. http://dx.doi.org/10.1017/jfm.2016.150.
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The interaction of the barotropic tide with a tall, two-dimensional ridge is examined analytically and numerically at latitudes where the tide is subinertial, and contrasted to when the tide is superinertial. When the tide is subinertial, the energy density associated with the response grows with latitude as both the oscillatory along-ridge flow and near-ridge isopycnal displacement become large. Where $f\neq 0$, nonlinear processes lead to the formation of along-ridge jets, which become faster at high latitudes. Dissipation and mixing is larger, and peaks later in the tidal cycle when the tide is subinertial compared with when the tide is superinertial. Mixing occurs mainly on the flanks of the topography in both cases, though a superinertial tide may additionally generate mixing above topography arising from convective breaking of radiating waves.
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Klymak, Jody M., Sonya Legg, and Robert Pinkel. "A Simple Parameterization of Turbulent Tidal Mixing near Supercritical Topography." Journal of Physical Oceanography 40, no. 9 (September 1, 2010): 2059–74. http://dx.doi.org/10.1175/2010jpo4396.1.
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Abstract A simple parameterization for tidal dissipation near supercritical topography, designed to be applied at deep midocean ridges, is presented. In this parameterization, radiation of internal tides is quantified using a linear knife-edge model. Vertical internal wave modes that have nonrotating phase speeds slower than the tidal advection speed are assumed to dissipate locally, primarily because of hydraulic effects near the ridge crest. Evidence for high modes being dissipated is given in idealized numerical models of tidal flow over a Gaussian ridge. These idealized models also give guidance for where in the water column the predicted dissipation should be placed. The dissipation recipe holds if the Coriolis frequency f is varied, as long as hN/W ≫ f, where N is the stratification, h is the topographic height, and W is a width scale. This parameterization is not applicable to shallower topography, which has significantly more dissipation because near-critical processes dominate the observed turbulence. The parameterization compares well against simulations of tidal dissipation at the Kauai ridge but predicts less dissipation than estimated from observations of the full Hawaiian ridge, perhaps because of unparameterized wave–wave interactions.
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J. Fensham, R., and R. J. Fairfax. "Re-establishing the endangered grassland herb Trioncinia retroflexa (Asteraceae)." Pacific Conservation Biology 11, no. 2 (2005): 128. http://dx.doi.org/10.1071/pc050128.
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The endangered perennial herb Trioncinia retroflexa was re-established within suitable grassland habitat in central Queensland. The trial included direct seeding and transplanting nursery-grown seedlings during the wet season. Successful establishment may be contingent on moist surface soils at the time of planting and the maintenance of this moisture by adequate follow-up rain in the month after planting. Five years after planting there were a total of 22 mature plants and eight infertile plants within two small areas of the re-establishment trial. The established plants are now reproducing and several generations of seedlings have become established. Topographic position (ridges or swales) and post-planting fires had no significant effect on the density of the re-established population. There have been substantial fluctuations in the re-established population in concert with seasonal rainfall patterns. A patchy and small fe-established population could be expected given the patchiness of the largest natural population and the relatively low rainfall of the introduction site.
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Katsman, Caroline A. "Impacts of Localized Mixing and Topography on the Stationary Abyssal Circulation." Journal of Physical Oceanography 36, no. 8 (August 1, 2006): 1660–71. http://dx.doi.org/10.1175/jpo2925.1.
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Abstract Stommel and coworkers calculated the stationary, geostrophic circulation in the abyssal ocean driven by prescribed sources (representing convective downwelling sites) and sinks (slow, widespread upwelling through the thermocline). The applied basin geometries were highly idealized with nearly uniform upwelling and gradual bottom slopes. In this paper, the classical Stommel–Arons theory for the abyssal circulation is extended by introducing pronounced bathymetry in the form of a midocean ridge and strongly enhanced upwelling in the vicinity of this ridge, modeled after direct observations of diapycnal mixing rates in the deep ocean. Locally enhanced upwelling over a midocean ridge drives a β-plume circulation that is modified by topographic stretching. The dynamics of this abyssal circulation pattern are explained by analyzing the combined impacts of the upwelling pattern and the bathymetry on the stationary circulation, building on their well-known separate impacts. On the western flank of the ridge, the effects of topographic stretching and upwelling oppose, and the direction of the local flow depends on their relative size. In this paper, a simple theoretical estimate is derived that can predict the direction of the flow along the ridge based on the geometry of the basin and the upwelling region. Its applicability is demonstrated for both the idealized model configurations applied in this study and for more realistic model simulations.
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TSELUIKO, D., M. G. BLYTH, D. T. PAPAGEORGIOU, and J. M. VANDEN-BROECK. "Electrified viscous thin film flow over topography." Journal of Fluid Mechanics 597 (February 1, 2008): 449–75. http://dx.doi.org/10.1017/s002211200700986x.
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The gravity-driven flow of a liquid film down an inclined wall with periodic indentations in the presence of a normal electric field is investigated. The film is assumed to be a perfect conductor, and the bounding region of air above the film is taken to be a perfect dielectric. In particular, the interaction between the electric field and the topography is examined by predicting the shape of the film surface under steady conditions. A nonlinear, non-local evolution equation for the thickness of the liquid film is derived using a long-wave asymptotic analysis. Steady solutions are computed for flow into a rectangular trench and over a rectangular mound, whose shapes are approximated with smooth functions. The limiting behaviour of the film profile as the steepness of the wall geometry is increased is discussed. Using substantial numerical evidence, it is established that as the topography steepness increases towards rectangular steps, trenches, or mounds, the interfacial slope remains bounded, and the film does not touch the wall. In the absence of an electric field, the film develops a capillary ridge above a downward step and a slight depression in front of an upward step. It is demonstrated how an electric field may be used to completely eliminate the capillary ridge at a downward step. In contrast, imposing an electric field leads to the creation of a free-surface ridge at an upward step. The effect of the electric field on film flow into relatively narrow trenches, over relatively narrow mounds, and down slightly inclined substrates is also considered.
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Jiménez-Urias, Miguel A., and LuAnne Thompson. "Idealized Study on the Effect of Bottom Topography on the Seasonality of the Stability of the Iceland–Faeroe Front." Journal of Physical Oceanography 48, no. 12 (December 2018): 2989–3008. http://dx.doi.org/10.1175/jpo-d-18-0048.1.
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AbstractWe investigate the effects of bottom topography on the instability, eddy-driven heat flux, and overturning of a front that sits atop a ridge by varying the initial location of an idealized frontal outcrop with respect to a topographic ridge. The front is periodic in the along-ridge direction and unstable to both mixed layer and mesoscale baroclinic instabilities with both instabilities focused on the northern flank of the ridge where the front outcrops. We find agreement with the theoretical predictions for the development of mesoscale instability of the jet in the presence of sloping bottom topography, and we find the initial growth of surface mixed layer eddies is insensitive to topographic variations. However, during the finite amplitude phase of mixed layer instability, we find faster development of mesoscale eddies and thus a stronger cross-front eddy heat flux and residual circulation for the position of the jet where we found the faster growth of mesoscale baroclinic instability. Over an advective time scale that represents the transit time of a water parcel along the Iceland–Faeroe Ridge (IFR), the resulting eddy heat flux is greatest in the cases where the frontal jet experiences the most destabilizing bottom topography of the three cases tested, with values comparable to the heat flux associated with the mean flow. Therefore, eddy dynamics over the IFR frontal region are important contributors to the heat exchanges between the North Atlantic and Nordic Seas, with the bottom topography playing a key role in determining the largest heat fluxes, whether the initial growth is dominated by mixed layer eddies or mesoscale eddies.
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Nooren, Kees, Wim Z. Hoek, Tim Winkels, Annika Huizinga, Hans Van der Plicht, Remke L. Van Dam, Sytze Van Heteren, et al. "The Usumacinta–Grijalva beach-ridge plain in southern Mexico: a high-resolution archive of river discharge and precipitation." Earth Surface Dynamics 5, no. 3 (September 8, 2017): 529–56. http://dx.doi.org/10.5194/esurf-5-529-2017.
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Abstract. The beach-ridge sequence of the Usumacinta–Grijalva delta borders a 300 km long section of the southern Gulf of Mexico coast. With around 500 beach ridges formed in the last 6500 years, the sequence is unsurpassed in the world in terms of numbers of individual ridges preserved, continuity of the record, and temporal resolution. We mapped and dated the most extensively accreted part of the sequence, linking six phases of accretion to river mouth reconfigurations and constraining their ages with 14C and OSL dating. The geomorphological and sedimentological reconstruction relied on lidar data, coring transects, GPR measurements, grain-size analyses, and chemical fingerprinting of volcanic glass and pumice encountered within the beach and dune deposits. We demonstrate that the beach-ridge complex was formed under ample long-term fluvial sediment supply and shorter-term wave- and aeolian-modulated sediment reworking. The abundance of fluvially supplied sand is explained by the presence of easily weatherable Los Chocoyos ignimbrites from the ca. 84 ka eruption of the Atitlán volcano (Guatemala) in the catchment of the Usumacinta River. Autocyclic processes seem responsible for the formation of ridge–swale couplets. Fluctuations in their periodicity (ranging from 6–19 years) are governed by progradation rate, and are therefore not indicative of sea level fluctuations or variability in storm activity. The fine sandy beach ridges are mainly swash built. Ridge elevation, however, is strongly influenced by aeolian accretion during the time the ridge is located next to the beach. Beach-ridge elevation is negatively correlated with progradation rate, which we relate to the variability in sediment supply to the coastal zone, reflecting decadal-scale precipitation changes within the river catchment. In the southern Mexican delta plain, the coastal beach ridges therefore appear to be excellent recorders of hinterland precipitation.
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Hautot, Sophie, Pascal Tarits, Frédéric Perrier, Corinne Tarits, and Michael Trique. "Groundwater electromagnetic imaging in complex geological and topographical regions: A case study of a tectonic boundary in the French Alps." GEOPHYSICS 67, no. 4 (July 2002): 1048–60. http://dx.doi.org/10.1190/1.1500365.
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Very‐low‐frequency (VLF), audiomagnetotelluric (AMT), and water geochemistry surveys were performed on the Sur‐Frêtes Ridge in the French Alps to evaluate the groundwater circulation system within the ridge. At this site, temporal variations of the electric field have been observed in association with water‐level variations of neighboring artificial lakes. The Sur‐Frêtes Ridge is 1 km wide and trends east–west. Water samples were collected at 52 points distributed throughout the area. VLF soundings were carried out along three parallel east–west profiles, and 7 AMT soundings were carried out along an east–west profile on the top of the ridge. This site is characterized by a rugged topography of the ridge where geological and topographic trends are almost perpendicular, making the structure fully three dimensional. We constructed a 2‐D resistivity model of the ridge from 2‐D and 3‐D analyses of the VLF and AMT data, associating geology and topography models. When combined with the water chemistry data, a model is proposed for groundwater percolation below the ridge across the geological contacts. This study demonstrates that electromagnetic imaging in a highly heterogeneous context can be combined with water chemistry to map groundwater circulation at the kilometer scale. The approach is relevant for hydrogeological and environmental applications.
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Narayan, J. P., and A. Kumar. "Quantification of Effects of Ridge and Valley Topography on the Rayleigh Wave Characteristics." Journal of Earthquake and Tsunami 12, no. 03 (August 12, 2018): 1850007. http://dx.doi.org/10.1142/s1793431118500070.
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The effects of ridge and valley on the characteristics of Rayleigh waves are presented in this paper. The research work carried out has been stimulated by the day by day increase of long-span structures in the hilly areas which are largely affected by the spatial variability in ground motion caused by the high-frequency Rayleigh waves. The Rayleigh wave responses of the considered triangular and elliptical ridge and valley models were computed using a fourth-order accurate staggered-grid viscoelastic P-SV wave finite-difference (FD) program. The simulated results revealed very large amplification of the horizontal component and de-amplification of the vertical component of Rayleigh wave at the top of a triangular ridge and de-amplification of both the components at the base of the triangular valley. The observed amplification of both the components of Rayleigh wave in front of elliptical valley was larger than triangular valley models. A splitting of the Rayleigh wave wavelet was inferred after interaction with ridge and valley. It is concluded that the large-scale topography acts as a natural insulator for the surface waves and the insulating capacity of the valley is more than that of a ridge. This insulation phenomenon is arising due to the reflection, diffraction and splitting of the surface wave while moving across the topography. It is concluded that insulating potential of the topography for the Rayleigh waves largely depends on their shape and shape-ratio.
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Smith, Lauren A., David M. Eissenstat, and Margot W. Kaye. "Variability in aboveground carbon driven by slope aspect and curvature in an eastern deciduous forest, USA." Canadian Journal of Forest Research 47, no. 2 (February 2017): 149–58. http://dx.doi.org/10.1139/cjfr-2016-0147.
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In forested ecosystems, topography and tree species contribute to spatial variability in carbon (C) dynamics through differential rates of C uptake and storage; therefore, estimates of species-specific and spatial variability in C can strengthen ecosystem budgets. To produce such estimates, we deconstructed watershed-scale C and component pools (e.g., wood biomass, litter) and fluxes at a fine scale using a small mixed deciduous forest catchment to determine the variation due to topographic position and species. Factors affecting fluxes included aspect, slope curvature, tree species contributions, and litter production. Annual C uptake into wood varied across the catchment from 0 to 34 kg C·year−1 and was 20% greater on southern aspects than northern ones and 33% greater in swales than non-swale slopes. Of the more than 20 tree species found in the forest canopy of the catchment, highest C uptake in woody biomass was measured in Quercus rubra L. growing in swales, followed by Quercus prinus L. syn. growing on the southern aspect, with the lowest aboveground wood increment measured in Pinus at higher elevations on non-swale slopes. Quercus leaf litter moved from where it dropped into litter traps to where it settled on the forest floor, shifting the location of litter C inputs to the soil. Local variation in aboveground C rivals regional variation across regions and has the potential to introduce error when scaling C measures from points to landscapes.
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Chen, Yongshun, and W. Jason Morgan. "A nonlinear rheology model for mid-ocean ridge axis topography." Journal of Geophysical Research 95, B11 (1990): 17583. http://dx.doi.org/10.1029/jb095ib11p17583.
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Golombek, M. P., F. S. Anderson, and M. T. Zuber. "Martian wrinkle ridge topography: Evidence for subsurface faults from MOLA." Journal of Geophysical Research: Planets 106, E10 (October 1, 2001): 23811–21. http://dx.doi.org/10.1029/2000je001308.
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Ellett, D. J. "Bottom topography to the west of the Wyville-Thomson Ridge." Deutsche Hydrographische Zeitschrift 41, no. 1 (January 1988): 23–33. http://dx.doi.org/10.1007/bf02308040.
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Matsumura, Yoshimasa, and Hiroyasu Hasumi. "Dynamics of Cross-Isobath Dense Water Transport Induced by Slope Topography." Journal of Physical Oceanography 41, no. 12 (December 1, 2011): 2402–16. http://dx.doi.org/10.1175/jpo-d-10-05014.1.
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Abstract Dynamics of cross-isobath downslope transport of a dense water mass induced by small-scale topographic variation is investigated based on a high-resolution numerical experiment with realistic settings, a simplified analytical model for water particle advection, and idealized sensitivity experiments. The existence of a submarine ridge induces two different processes for cross-isobath downslope transport of dense water: a strong but narrow and thin downslope current at the east side of the ridge and cyclonic eddies with dense water cores to the west of the ridge. The former downslope current is produced in response to the rapid increase of slope angle near the ridge. The latter eddies are formed by stretching of the dense water layer near the crest, where isobath curvature is so high that offshore centrifugal force overcomes the coastward Coriolis force. From a simple analysis on the equation of motion for a fluid particle placed on a slope with curved isobaths, a general criterion that describes whether a density current follows or crosses isobaths is derived, which is supported by idealized sensitivity experiments. The location where cross-isobath transport of dense water takes place is determined by relative magnitude between spatial derivatives of isobath curvature, planetary vorticity, and slope angle. Based on these arguments, a parameterization is proposed to represent the effect of unresolved small-scale topography in coarse-resolution models.
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Jiang, Qingfang. "Applicability of Reduced-Gravity Shallow-Water Theory to Atmospheric Flow over Topography." Journal of the Atmospheric Sciences 71, no. 4 (March 27, 2014): 1460–79. http://dx.doi.org/10.1175/jas-d-13-0101.1.
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Abstract Applicability of the reduced-gravity shallow-water (RGSW) theory to a shallow atmospheric layer capped by an inversion underneath a deep stratified atmosphere over a two-dimensional ridge has been investigated using linear analysis and nonlinear numerical simulations. Two key nondimensional parameters are identified: namely, and , where g′ is the reduced-gravity acceleration; H0 is the RGSW layer depth; and N and U are the buoyancy frequency and wind speed, respectively, in the layer above the inversion. If J and γ are around unity or larger, the response of the RGSW flow over the ridge can be significantly modified by pressure perturbations aloft. Any jumplike perturbations in the RGSW layer rapidly decay while propagating away from the ridge as the perturbation energy radiates into the upper layer. With J and γ much less than unity, RGSW theory is more adequate for describing RGSW flows. In addition, inversion splitting occurs downstream of a jump when , where Ni is the buoyancy frequency in the inversion and hm stands for the ridge height. A less stratified upper layer with slower winds in general has less influence on the RGSW flow below and favors the application of the RGSW theory. For a thick inversion (d), the equivalent RGSW flow depth is approximately given by H + d/2, where H is the depth of the neutral layer below the inversion.
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Klymak, Jody M., Robert Pinkel, and Luc Rainville. "Direct Breaking of the Internal Tide near Topography: Kaena Ridge, Hawaii." Journal of Physical Oceanography 38, no. 2 (February 1, 2008): 380–99. http://dx.doi.org/10.1175/2007jpo3728.1.
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Abstract Barotropic to baroclinic conversion and attendant phenomena were recently examined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two distinct mixing processes appear to be at work in the waters above the 1100-m-deep ridge crest. At middepths, above 400 m, mixing events resemble their open-ocean counterparts. There is no apparent modulation of mixing rates with the fortnightly cycle, and they are well modeled by standard open-ocean parameterizations. Nearer to the topography, there is quasi-deterministic breaking associated with each baroclinic crest passage. Large-amplitude, small-scale internal waves are triggered by tidal forcing, consistent with lee-wave formation at the ridge break. These waves have vertical wavelengths on the order of 400 m. During spring tides, the waves are nonlinear and exhibit convective instabilities on their leading edge. Dissipation rates exceed those predicted by the open-ocean parameterizations by up to a factor of 100, with the disparity increasing as the seafloor is approached. These observations are based on a set of repeated CTD and microconductivity profiles obtained from the research platform (R/P) Floating Instrument Platform (FLIP), which was trimoored over the southern edge of the ridge crest. Ocean velocity and shear were resolved to a 4-m vertical scale by a suspended Doppler sonar. Dissipation was estimated both by measuring overturn displacements and from microconductivity wavenumber spectra. The methods agreed in water deeper than 200 m, where sensor resolution limitations do not limit the turbulence estimates. At intense mixing sites new phenomena await discovery, and existing parameterizations cannot be expected to apply.
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Adams, Samuel D. M., Richard V. Craster, and Duncan P. Williams. "Rayleigh waves guided by topography." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2078 (October 17, 2006): 531–50. http://dx.doi.org/10.1098/rspa.2006.1779.
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We consider wave propagation along the surface of an elastic half-space, whose surface is flat except for a straight, infinite length, ridge or trench that does not vary in its cross-section. We seek to resolve the issue of whether such a perturbed surface can support a trapped wave, whose energy is localized to within some vicinity of the defect, and explain physically how this trapping occurs. First, the trapping is addressed by developing an asymptotic scheme, which exploits a small parameter associated with the surface variation, to perturb about the base state of a flat half-space (which supports a surface wave, as demonstrated by Lord Rayleigh in 1885). We then provide convincing numerical evidence to support the results obtained from the asymptotic scheme; however, no rigorous proof of existence is presented.
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Ramos, Victor A. "Seismic ridge subduction and topography: Foreland deformation in the Patagonian Andes." Tectonophysics 399, no. 1-4 (April 2005): 73–86. http://dx.doi.org/10.1016/j.tecto.2004.12.016.
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Eaton, Gordon P. "Topography and origin of the southern Rocky Mountains and Alvarado Ridge." Geological Society, London, Special Publications 28, no. 1 (1987): 355–69. http://dx.doi.org/10.1144/gsl.sp.1987.028.01.22.
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CENEDESE, C., and P. F. LINDEN. "Stability of a buoyancy-driven coastal current at the shelf break." Journal of Fluid Mechanics 452 (February 10, 2002): 97–121. http://dx.doi.org/10.1017/s0022112001006668.
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Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.
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Werner, F. A., J. Homeier, M. Oesker, and J. Boy. "Epiphytic biomass of a tropical montane forest varies with topography." Journal of Tropical Ecology 28, no. 1 (December 8, 2011): 23–31. http://dx.doi.org/10.1017/s0266467411000526.
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Abstract:The spatial heterogeneity of tropical forest epiphytes has rarely been quantified in terms of biomass. In particular, the effect of topographic variation on epiphyte biomass is poorly known, although forests on ridges and ravines can differ drastically in stature and exposure. In an Ecuadorian lower montane forest we quantified epiphytic biomass along two gradients: (1) the twig–branch–trunk trajectory, and (2) the ridge–ravine gradient. Twenty-one trees were sampled in each of three forest types (ridge, slope, ravine positions). Their epiphytic biomass was extrapolated to stand level based on basal area–epiphyte load relationships, with tree basal areas taken from six plots of 400 m2 each per forest type. Our results document the successional addition and partial replacement of lichens by bryophytes, angiosperms and finally dead organic matter along the twig–branch–trunk trajectory. Despite having the highest tree basal area, total epiphytic biomass (mean ± SD) of ravine forest was significantly lower (2.6 ± 0.7 Mg ha−1) than in mid-slope forest (6.3 ± 1.1 Mg ha−1) and ridge forest (4.4 ± 1.6 Mg ha−1), whereas maximum bryophyte water storage capacity was significantly higher. We attribute this pattern to differences in forest dynamics, stand structure and microclimate. Although our study could not differentiate between direct effects of slope position (nutrient availability, mesoclimate) and indirect effects (stand structure and dynamics), it provides evidence that fine-scale topography needs to be taken into account when extrapolating epiphytic biomass and related matter fluxes from stand-level data to the regional scale.
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Jiang, Qingfang, James D. Doyle, Shouping Wang, and Ronald B. Smith. "On Boundary Layer Separation in the Lee of Mesoscale Topography." Journal of the Atmospheric Sciences 64, no. 2 (February 1, 2007): 401–20. http://dx.doi.org/10.1175/jas3848.1.
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Abstract The onset of boundary layer separation (BLS) forced by gravity waves in the lee of mesoscale topography is investigated based on a series of numerical simulations and analytical formulations. It is demonstrated that BLS forced by trapped waves is governed by a normalized ratio of the vertical velocity maximum to the surface wind speed; other factors such as the mountain height, mountain slope, or the leeside speedup factor are less relevant. The onset of BLS is sensitive to the surface sensible heat flux—a positive heat flux tends to increase the surface wind speed through enhancing the vertical momentum mixing and accordingly inhibits the occurrence of BLS, and a negative heat flux does the opposite. The wave forcing required to cause BLS decreases with an increase of the aerodynamical roughness zo; a larger zo generates larger surface stress and weaker surface winds and therefore promotes BLS. In addition, BLS shows some sensitivity to the terrain geometry, which modulates the wave characteristics. For a wider ridge, a higher mountain is required to generate trapped waves with a wave amplitude comparable to that generated by a lower but narrower ridge. The stronger hydrostatic waves associated with the wider and higher ridge play only a minor role in the onset of BLS. It has been demonstrated that although hydrostatic waves generally do not directly induce BLS, undular bores may form associated with wave breaking in the lower troposphere, which in turn induce BLS. In addition, BLS could occur underneath undular jump heads or associate with trapped waves downstream of a jump head in the presence of a low-level inversion.
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Lee, Rachel M., Leonard Campanello, Matt J. Hourwitz, Phillip Alvarez, Ava Omidvar, John T. Fourkas, and Wolfgang Losert. "Quantifying topography-guided actin dynamics across scales using optical flow." Molecular Biology of the Cell 31, no. 16 (July 21, 2020): 1753–64. http://dx.doi.org/10.1091/mbc.e19-11-0614.
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Two cell types with different migratory behaviors both exhibit guided actin polymerization along nanoscale ridge textures. Optical flow, a tool used in autonomous vehicles and facial recognition, is adapted for fluorescence imaging. The power of optical flow as a tool for future studies of intracellular dynamics is demonstrated.
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Lockwood, A. M., and C. D’Ercole. "THE EVOLUTION OF THE BERNIER RIDGE, SOUTHERN CARNARVON BASIN, WESTERN AUSTRALIA:IMPLICATIONS FOR PETROLEUM PROSPECTIVITY." APPEA Journal 44, no. 1 (2004): 241. http://dx.doi.org/10.1071/aj03009.
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The basement topography of the Gascoyne Platform and adjoining areas in the Southern Carnarvon Basin was investigated using satellite gravity and seismic data, assisted by a depth to crystalline basement map derived from modelling the isostatic residual gravity anomaly. The resulting enhanced view of the basement topography reveals that the Gascoyne Platform extends further westward than previously indicated, and is bounded by a northerly trending ridge of shallow basement, named the Bernier Ridge.The Bernier Ridge is a product of rift-flank uplift prior to the Valanginian breakup of Gondwana, and lies east of a series of small Mesozoic syn-rift sedimentary basins. Extensive magmatic underplating of the continental margin associated with this event, and a large igneous province is inferred west of the ridge from potential field and seismic data. Significant tectonic events that contributed to the present form of the Bernier Ridge include the creation of the basement material during the Proterozoic assembly of Rodinia, large-scale faulting during the ?Cambrian, uplift and associated glaciation during the early Carboniferous, and rifting of Gondwana during the Late Jurassic. The depositional history and maturity of the Gascoyne Platform and Bernier Ridge show that these terrains have been structurally elevated since the mid-Carboniferous.No wells have been drilled on the Bernier Ridge. The main source rocks within the sedimentary basins west of the Bernier Ridge are probably Jurassic, similar to those in the better-known Abrolhos–Houtman and Exmouth Sub-basins, where they are mostly early mature to mature and within the oil window respectively. Within the Bernier Ridge area, prospective plays for petroleum exploration in the Jurassic succession include truncation at the breakup unconformity sealed by post-breakup shale, and tilted fault blocks sealed by intraformational shale. Plays in the post-breakup succession include stratigraphic traps and minor rollover structures.
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Chapman, Christopher C., and Rosemary Morrow. "Variability of Southern Ocean Jets near Topography." Journal of Physical Oceanography 44, no. 2 (February 1, 2014): 676–93. http://dx.doi.org/10.1175/jpo-d-13-0182.1.
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Abstract The interaction of jets with topography in the Southern Ocean is investigated using 19 years of altimetry data. In particular, the “jet jumping” mode of variability, by which two or more jets passing close to the same topographic feature show strongly anticorrelated strengthening and weakening, is studied. Three regional case studies are described—the Southeast Indian Ridge south of Tasmania, the Macquarie Ridge south of New Zealand, and the Pacific–Antarctic Rise—where the jet jumping variability is found to occur. Using principal component analysis, the spatial patterns of variability show a vortex dipole forming on either side of a particular jet. For each regional study, it is found that the variability in strength of these vortices (as measured by the spatially averaged vorticity) is strongly correlated with time series of the principle component that describes the jet jumping variability. The observational analysis is complemented by a suite of idealized numerical experiments using a three-layer quasigeostrophic model with simple topography. The numerical results show similar spatial patterns of variability to those observed in the altimetric data. Internal variability is sufficient to generate jet jumping variability, as there is no time-varying external forcing applied in the model configuration. The simulations are used to investigate the effect of topographic scale and changing bottom friction. The authors find that both have a strong influence on the time scale of the variability, with larger topographic scales and higher bottom friction leading to faster time scales. This study shows that even in regions where the flow is strongly influenced by topography, Southern Ocean jet flow may exhibit low-frequency variability.
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Gaberšek, Saša, and Dale R. Durran. "Gap Flows through Idealized Topography. Part II: Effects of Rotation and Surface Friction." Journal of the Atmospheric Sciences 63, no. 11 (November 1, 2006): 2720–39. http://dx.doi.org/10.1175/jas3786.1.
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Abstract Numerical simulations are conducted of geostrophically balanced flow over an isolated mountain cut by a horizontal gap. The relative importance of the along-gap synoptic-scale pressure gradient and terrain-induced mesoscale circulations for the generation of gap winds was examined by changing the direction of the synoptic-scale wind relative to the topography. In all cases, the forcing associated with mesoscale circulations generated by the mountain was at least as significant as the synoptic-scale pressure gradient. In the cases where a component of the large-scale flow was directed perpendicular to the ridge, the dynamics were dominated by either the vertical momentum fluxes due to mountain lee waves or by mesoscale pressure gradients associated with upstream blocking or lee troughing. Mesoscale circulations were also important when the large-scale flow was parallel to the ridge because surface friction turned the low-level winds toward the high pressure side of the ridge, partially blocking the flow and enhancing the along-gap pressure gradient. The flow in the interior of a very long uniform gap was also simulated for a case with the synoptic-scale winds parallel to the ridge so that the synoptic-scale pressure gradient was down the gap. The flow in the interior of the long gap was not horizontal and not in a simple dynamical balance between acceleration, the pressure gradient force, and surface friction. Even the flow in the lowest 150 m was gradually subsiding. Subsidence and lateral momentum flux convergence at low levels near the center of the gap were important contributors to the mass and along-gap momentum budgets.
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Chen, Chen-Yuan, Cheng-Wu Chen, and I.-Fan Tseng. "Localized Mixing Due to an Interfacial Solitary Wave Breaking on Seabed Topography in Different Ridge Heights." Journal of Offshore Mechanics and Arctic Engineering 129, no. 3 (September 12, 2006): 245–50. http://dx.doi.org/10.1115/1.2426991.
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Experiments were carried out in a wave flume on internal solitary wave (ISW) of depression-type propagating over a submarine ridge in triangular shape. Tests were arranged in series from combinations of submarine ridges in different height and ISW in different wave amplitudes. The resultant wave motions were found differing from that of surface gravity waves. Experimental results suggested the blockage parameter ζ can be applied to classify various degrees of ISW–ridge interaction, i.e., ζ<0.5 for weak encounter, 0.5<ζ<0.7 for moderate encounter, and 0.7<ζ for wave breaking. In addition, three categories of ISW–ridge interaction were also employed by the relationship between the degree of blocking B and dimensionless wave amplitude ai∕H2.
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Nadeau, Louis-Philippe, and Raffaele Ferrari. "The Role of Closed Gyres in Setting the Zonal Transport of the Antarctic Circumpolar Current." Journal of Physical Oceanography 45, no. 6 (June 2015): 1491–509. http://dx.doi.org/10.1175/jpo-d-14-0173.1.
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AbstractEddy-permitting simulations are used to show that basinlike gyres can be observed in the large-scale barotropic flow of a wind-driven channel with a meridional topographic ridge. This is confirmed using both two-layer quasigeostrophic and 25-level primitive equation models at high horizontal resolution. Comparing results from simulations with and without the topographic ridge, it is shown that the zonal baroclinic transport in the channel increases with increasing wind stress when the bottom topography is flat but not when there is a meridional ridge. The saturation of transport for increasing wind occurs in conjunction with the development of recirculating gyres in the large-scale barotropic streamfunction. This suggests that the total circulation can be thought of as a superposition of a gyre mode (which has zero circumpolar transport) and a free circumpolar mode (which contains all of the transport). Basinlike gyres arise in the channel because the topography steers the barotropic streamlines and supports a frictional boundary layer similar to the more familiar ones observed along western boundaries. The gyre mode is thus closely linked with the bottom form stress exerted by the along-ridge flow and provides the sink for the wind momentum input. In this framework, any increase in wind forcing spins a stronger gyre as opposed to feeding the circumpolar transport. This hypothesis is supported with a suite of experiments where key parameters are carried over a wide range: wind stress, wind stress curl, ridge height, channel length, and bottom friction.