The main purpose of this work is to show how a continuous finite bandwidth modes can be readily incorporated into the description post-critical Rayleigh-Bénard convection by use slowly varying (in space and time) amplitudes. Previous attempts have used multimodal discrete analysis. We that in addition obtaining results consistent with mode approach, there larger class stable realizable solutions. feature these solutions amplitude wave-number motion most unstable almost everywhere, but,...

Many oceanic island basalts show sublinear subparallel arrays in Sr-Nd-Pb isotopic space. The depleted upper mantle is rarely a mixing end-member of these arrays, as would be expected if plumes originated at 670-kilometer boundary layer and entrained during ascent. Instead, the are fan-shaped appear to converge on volume space characterized by low 87 Sr/ 86 Sr high 143 Nd/ 144 Nd, 206 Pb/ 204 Pb, 3 He/ 4 He ratios. This new component may lower mantle, into originating from core-mantle layer.

This study examines water property distributions in the deep South China Sea and adjoining Pacific Ocean using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from into through Luzon Strait. Applying hydraulic theory with assumptions of zero potential vorticity flat bottom to Strait yields transport estimate 2.5 Sv (1 = 10 6 3 s −1 ). Some implications this result include: (1) residence time less...

An experiment on the stability of convection rolls with varying wave-number is described in extension earlier work by Chen & Whitehead (1968). The results agree theoretical predictions Busse (1967 a ) and show two distinct types instability form non-oscillatory disturbances. ‘zigzag instability’ corresponds to bending original rolls; ‘cross-roll emerge at right angles rolls. At Rayleigh numbers above 23,000 are unstable for all wave-numbers replaced three-dimensional stationary which...

A similarity solution has been developed for vertical, steady‐state mantle plume conduits by considering the boundary layer flow emanating from a point source of heat in an axisymmetric geometry. This model includes effects temperature and shear stress on viscosity, incorporates depth‐dependent viscosity thermal expansivity. Plumes with variable have upward velocities 0.30–100 m/yr radii 30–250 km, depending temperature, rheology buoyancy flux. These results demonstrate small lateral scale...

We demonstrate finite structures formed as a consequence of the “reactive infiltration instability” (Chadam et al., 1986) in series laboratory and numerical experiments with growth solution channels parallel to fluid flow direction. Regions initially high porosity have ratios volume soluble solid surface area exhibit more rapid at constant pressure, so that dissolution reactions these regions produce relatively increase porosity. As grow, large ones entrain laterally inward extend rapidly....

We present results of a theoretical study aimed at understanding melt extraction from the upper mantle. Specifically, we address mechanisms for focusing porous flow into conduits beneath mid‐ocean ridges in order to explain observation that most oceanic residual peridotites are not equilibrium with ridge basalt. The existence such might also geological features, termed replacive dunites, observed exposed mantle sections. show here, by linear analysis, chemically reactive media is unstable...

First Page

Theoretical and laboratory models of certain types strait sill flows are discussed. Specifically, we consider a two‐layer rotating fluid; the upper layer is at rest lower from one large basin to another via connecting channel. The flow assumed be principally in down‐channel direction. cross‐channel balance therefore geostrophic Bernoulli potential vorticity equations simplified. We further invoke usual non‐rotating hydraulic principle maximum transport over weir—here end channel—and thereby...

An experimental study of transitions from steady bimodal convection to time-dependent forms is described. Using controlled initial conditions for the onset two mechanisms instability can be separated effects random noise. The oscillatory cells introduces standing waves closely resembling those occurring in low Prandtl number convection. collective spoke-pattern which characteristic turbulent large Both instabilities originate primarily momentum advection terms equations motion, as evident...

By introducing small controlled perturbations prior to the onset of motion, two-dimensional convection cells arbitrary width-depth ratios are produced in a horizontal fluid layer heated from below. The conditions employed correspond finite-amplitude Rayleigh stability problem for constant viscosity, large Prandtl number, Boussinesq with rigid, conducting boundaries. It was found that close unity stable at all numbers investigated (Rc [Lt ] R 2·5Rc). Cells whose widthdepth moderately too or...

Saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to next, depending on source bottom water. Flow in these appears be topographically controlled so interface water and above adjusts itself permit that contains a into next. Examples Atlantic include Romanche Fracture Zone, Vema Channel, Ceara Abyssal Plain, Anegada‐Jungfern passage, Discovery Gap, but there many more. Theoretical predictions volume flux using method requires only...

A density-driven current was generated in the laboratory by releasing dense fluid over a sloping bottom rotating freshwater system. The behavior of descending slope has been investigated systematically varying four parameters: rotation rate, slope, flow rate fluid, and density fluid. Over wide range parameter values, following three types were found: laminar regime which had constant thickness behind head, wave wavelike disturbances appeared on interface between fresh fluids, an eddy...

When light rotating fluid spreads over heavier in the vicinity of a vertical wall (coast) boundary jet width Λ forms, leading edge or nose which propagates with speed ĉ along coast. A certain fraction 8 transport is not carried by but deflected backwards (detrained) and left behind propagating nose. Theoretical experimental results for Λ,ĉ, δ are given quasi-equilibrium (constant-ĉ) regime. Over longer time intervals laboratory observations suggest that slows down stagnates, whereupon...

Calculation was made of the northward flow Antarctic Bottom Water into western North Atlantic Basin through a passageway approximately 300 km wide between Ceara Rise and Mid‐Atlantic Ridge at about 4°N. Two moorings carrying four current meters each were placed in region where currents expected to be greatest left for 360 days. The not steady, but exhibited large surges with 60‐day time scale whose cause is unknown. Current fastest flowing all net flow. It estimated that 0.8×10 6 m 3 s −1...

A bunsen flame rotated under a cylindrical annulus filled with liquid mercury forces the to rotate in direction counter that of rotating flame. The rate rotation is several times greater than This observation may provide an explanation for high velocities apparent cloud formations upper atmosphere Venus.

Water with constant initial salt stratification was mixed a horizontally moving vertical rod. The initially linear density profile turned into series of steps when mixing weak, in agreement instability theory by Phillips (1972) and Posmentier (1977). For stronger no formed. However, all cases layers formed next to the top bottom boundaries expanded interior due no-flux condition at horizontal boundaries. critical Richardson number Ri e , dividing experiments ones without, increases Reynolds...

Magma chambers, particularly those of basaltic composition, are often replenished by an influx magma whose density is less than that the resident magma. This paper describes fundamental fluid mechanics involved in replenishment light inputs. If ρ denotes uniform and — Δρ input, situation described reduced gravity g ’ = Δρ/ρ, volume flux Q , viscosities input magmas ν e i respectively. The (nondimensional) Reynolds numbers, Re ( 3 ) 1/5 /ν chamber geometry then completely specify system. For...