scholarly journals Coriolis forces influence the secondary circulation of gravity currents flowing in large-scale sinuous submarine channel systems

2010 ◽  
Vol 37 (17) ◽  
pp. n/a-n/a ◽  
Author(s):  
Remo Cossu ◽  
Mathew G. Wells
Keyword(s):  
Large Scale ◽  
Gravity Currents ◽  
Secondary Circulation ◽  
Coriolis Forces ◽  
Submarine Channel ◽  
Channel Systems

scholarly journals The possible role of Coriolis forces in structuring large-scale sinuous patterns of submarine channel–levee systems

2013 ◽  
Vol 371 (2004) ◽  
pp. 20120366 ◽  
Author(s):  
Mathew Wells ◽  
Remo Cossu
Keyword(s):  
Large Scale ◽  
Deep Ocean ◽  
Turbidity Currents ◽  
Radius Of Curvature ◽  
Coriolis Parameter ◽  
Coriolis Forces ◽  
Density Interface ◽  
Submarine Channel ◽  
Northern Latitudes ◽  
The Right

Submarine channel–levee systems are among the largest sedimentary structures on the ocean floor. These channels have a sinuous pattern and are the main conduits for turbidity currents to transport sediment to the deep ocean. Recent observations have shown that their sinuosity decreases strongly with latitude, with high-latitude channels being much straighter than similar channels near the Equator. One possible explanation is that Coriolis forces laterally deflect turbidity currents so that at high Northern latitudes both the density interface and the downstream velocity maximum are deflected to the right-hand side of the channel (looking downstream). The shift in the velocity field can change the locations of erosion and deposition and introduce an asymmetry between left- and right-turning bends. The importance of Coriolis forces is defined by two Rossby numbers, Ro W = U / Wf and Ro R = U / Rf , where U is the mean downstream velocity, W is the width of the channel, R is the radius of curvature and f is the Coriolis parameter. In a bending channel, the density interface is flat when Ro R ∼−1, and Coriolis forces start to shift the velocity maximum when | Ro W |<5. We review recent experimental and field observations and describe how Coriolis forces could lead to straighter channels at high latitudes.

scholarly journals Energy Transfer in Contact Binaries

1976 ◽  
Vol 73 ◽  
pp. 333-333
Author(s):  
A. P. Moses ◽  
R. C. Smith
Keyword(s):  
Energy Transfer ◽  
Large Scale ◽  
Approximate Model ◽  
Convective Envelope ◽  
Large Scale Circulation ◽  
Coriolis Forces ◽  
Contact Binaries ◽  
Contact Binary ◽  
The Common ◽  
Major Factors

The anomalous mass-luminosity relation for the components of a contact binary system is usually explained by postulating strong energy transfer from the primary to the secondary. It has been assumed that the transfer occurs in the common convective envelope surrounding the two stars, but so far the only attempt at a model for the energy transfer has been the sideways convection model of Hazlehurst and Meyer-Hofmeister (1973), which assumes a large-scale circulation of material between the two components.Any detailed discussion of the dynamics in the common envelope must take account of the predominantly vertical motions associated with normal thermal convection, of Coriolis forces and of viscosity. We have constructed an approximate model for the horizontal transfer of energy between the two components, using a mixing-length approach and taking all three factors into account. The major factors are the vertical convection and the Coriolis forces, which together prevent a large-scale circulation of the type proposed by Hazlehurst and Meyer-Hofmeister. Instead, the flow breaks up into smallscale eddies whose horizontal scale is determined by the interaction of convection, Coriolis forces and viscosity. This has the important qualitative consequence that horizontal energy transfer will occur only if the mean horizontal pressure gradient between the two stars exceeds a certain minimum value. This condition can easily be satisfied in the adiabatic zone of the envelope, but may be an important restriction in the super-adiabatic zone.Using our model, we were able to estimate the entropy difference between components which is required to transfer enough energy to explain the observed mass-luminosity relation. We found that equal entropy models are possible only if the contact is deep. Unequal entropy models are possible for any degree of contact, so long as the contact extends down as far as the adiabatic zone. If, as has been suggested, the depth of contact increases during evolution then zero-age models must have shallow contact and hence unequal entropies. Deep contact equal entropy models would then form as a result of evolution.A difficulty is that in our model insufficient energy transfer can occur in the super-adiabatic zone to produce WUMa light curves for the unequal entropy models. This may mean that further work is needed on the exact surface conditions in these stars.

Entraining gravity currents

2013 ◽  
Vol 731 ◽  
pp. 477-508 ◽  
Author(s):  
Christopher G. Johnson ◽  
Andrew J. Hogg
Keyword(s):  
Richardson Number ◽  
Solution Structure ◽  
Large Scale ◽  
Gravity Current ◽  
Gravity Currents ◽  
Similarity Solutions ◽  
Water Model ◽  
Experimental Measurements ◽  
Entrainment Rate ◽  
Long Time

AbstractEntrainment of ambient fluid into a gravity current, while often negligible in laboratory-scale flows, may become increasingly significant in large-scale natural flows. We present a theoretical study of the effect of this entrainment by augmenting a shallow water model for gravity currents under a deep ambient with a simple empirical model for entrainment, based on experimental measurements of the fluid entrainment rate as a function of the bulk Richardson number. By analysing long-time similarity solutions of the model, we find that the decrease in entrainment coefficient at large Richardson number, due to the suppression of turbulent mixing by stable stratification, qualitatively affects the structure and growth rate of the solutions, compared to currents in which the entrainment is taken to be constant or negligible. In particular, mixing is most significant close to the front of the currents, leading to flows that are more dilute, deeper and slower than their non-entraining counterparts. The long-time solution of an inviscid entraining gravity current generated by a lock-release of dense fluid is a similarity solution of the second kind, in which the current grows as a power of time that is dependent on the form of the entrainment law. With an entrainment law that fits the experimental measurements well, the length of currents in this entraining inviscid regime grows with time approximately as ${t}^{0. 447} $. For currents instigated by a constant buoyancy flux, a different solution structure exists in which the current length grows as ${t}^{4/ 5} $. In both cases, entrainment is most significant close to the current front.

scholarly journals HISTORY OF THE CHANNEL SYSTEMS REORGANIZATION OF THE KAMA-KELTMA LOWLAND IN THE LATE PLEISTOCENE – HOLOCENE

2020 ◽  
pp. 6-17
Author(s):  
Nikolai N. Nazarov ◽  
◽  
Sergei V. Kopytov ◽  
Keyword(s):  
Late Pleistocene ◽  
Radiocarbon Dating ◽  
Large Scale ◽  
Bottom Relief ◽  
Short Term ◽  
Second Stage ◽  
The Third ◽  
Third Stage ◽  
History Of ◽  
Channel Systems

The analysis of the actual data on the age and stages of the channel systems formation in the Kama-Keltma lowland was based on the altitudinal differentiation of different stages of the relief and the results of radiocarbon dating of organics from the channel and floodplain facies. Late Pleistocene lake terrace is the highest level in the Upper Kama depression and Keltma hollow. The research into the geomorphological structure and age of deposited materials, with a particular focus on separate elements of the Kama-Keltma lowland erosive and accumulative relief, indicates the existence of six stages of the channel systems formation (reorganization). The first stage (end of the Kalinin stadial) is the Chepets hollow formation. The hollow was preserved after large-scale changes in the bottom relief of the Upper Kama depression. The second stage (Mologa-Sheksna interstadial) is the first Kama terrace formation. The third stage (Ostashkov stadial, 20-18 ka) is the period of the runoff hollow formation (including the ‘large terrace hollow’), which actively dissected the surface of aeolian landforms. The fourth stage (LGM, 18-10 ka) is the formation of the macromeanders of the South Keltma, Pilva, and Timsher, as well as the multi-arm channel of the Kama during alternating periods of relatively short-term warming and cooling. The fifth stage is the wide Kama floodplain formation in the Preboreal – Subboreal, represented by segmental generations. The sixth stage (modern) is characterized by the ‘straightening’ of the Kama channel – the formation of a relatively straight channel throughout the Kama-Keltma lowland.

Compressible particle-driven gravity currents

2001 ◽  
Vol 445 ◽  
pp. 305-325 ◽  
Author(s):  
MARY-LOUISE E. TIMMERMANS ◽  
JOHN R. LISTER ◽  
HERBERT E. HUPPERT
Keyword(s):  
Large Scale ◽  
Numerical Solutions ◽  
Volcanic Eruptions ◽  
Gravity Currents ◽  
Scale Height ◽  
Pyroclastic Flows ◽  
Water Model ◽  
Model Approximation ◽  
Particle Settling ◽  
Density Scale

Large-scale particle-driven gravity currents occur in the atmosphere, often in the form of pyroclastic flows that result from explosive volcanic eruptions. The behaviour of these gravity currents is analysed here and it is shown that compressibility can be important in flow of such particle-laden gases because the presence of particles greatly reduces the density scale height, so that variations in density due to compressibility are significant over the thickness of the flow. A shallow-water model of the flow is developed, which incorporates the contribution of particles to the density and thermodynamics of the flow. Analytical similarity solutions and numerical solutions of the model equations are derived. The gas–particle mixture decompresses upon gravitational collapse and such flows have faster propagation speeds than incompressible currents of the same dimensions. Once a compressible current has spread sufficiently that its thickness is less than the density scale height it can be treated as incompressible. A simple ‘box-model’ approximation is developed to determine the effects of particle settling. The major effect is that a small amount of particle settling increases the density scale height of the particle-laden mixture and leads to a more rapid decompression of the current.

Turbulent Rotating Rayleigh–Benard Convection: Spatiotemporal and Statistical Study

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
A. Husain ◽  
M. F. Baig ◽  
H. Varshney
Keyword(s):  
Rayleigh Number ◽  
Kinetic Energy ◽  
Rotation Rate ◽  
Large Scale ◽  
Coriolis Forces ◽  
Large Scale Structures ◽  
Vertical Heat ◽  
Scale Structures ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

The present study involves a 3D numerical investigation of rotating Rayleigh–Benard convection in a large aspect-ratio (8:8:1) rectangular enclosure. The rectangular cavity is rotated about a vertical axis passing through the center of the cavity. The governing equations of mass, momentum, and energy for a frame rotating with the enclosure, subject to generalized Boussinesq approximation applied to the body and centrifugal force terms, have been solved on a collocated grid using a semi-implicit finite difference technique. The simulations have been carried out for liquid metal flows having a fixed Prandtl number Pr=0.01 and fixed Rayleigh number Ra=107 while rotational Rayleigh number Raw and Taylor number Ta are varied through nondimensional rotation rate (Ω) ranging from 0 to 104. Generation of large-scale structures is observed at low-rotation (Ω=10) rates though at higher-rotation rates (Ω=104) the increase in magnitude of Coriolis forces leads to redistribution of buoyancy-induced vertical kinetic energy to horizontal kinetic energy. This brings about inhibition of vertical fluid transport, thereby leading to reduced vertical heat transfer. The magnitude of rms velocities remains unaffected with an increase in Coriolis forces from Ω=0 to 104. An increase in rotational buoyancy (Raw), at constant rotation rate (Ω=104), on variation in Raw/Ta from 10−3 to 10−2 results in enhanced breakup of large-scale structures with a consequent decrease in rms velocities but with negligible reduction in vertical heat transport.

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