The effect of horizontal gradients on thermohaline convection

Thorpe, S. A.; Hutt, P. K.; Soulsby, R.L.

doi:10.1017/s0022112069000231

Cited by 196 publications

(97 citation statements)

References 9 publications

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“…A situation similar to the stratified Boycott effect arises in salt-stratified systems with heated vertical sidewalls (Thorpe et al 1969;Chen et al 1971), wherein buoyant up-welling is driven by the sidewalls. Once fluid from the base of the tank reaches its neutral buoyancy height, a primary intrusion develops.…”

Section: Discussionmentioning

confidence: 96%

“…At the initiation of the primary intrusion, the overlying boundary-layer fluid is also everywhere neutrally buoyant, and temperature and salinity gradients exist perpendicular to the wall. The resulting sideways diffusive instability (Hart 1971) initially proposed by Thorpe et al (1969) is then responsible for setting the length scale of secondary intrusions. We could likewise consider the possibility of an instability setting the length scale of the secondary layers in the stratified Boycott effect, using the approaches of Linden & Weber (1977) and Kerr (1991a).…”

Section: Discussionmentioning

confidence: 99%

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The stratified Boycott effect

2005

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We present the results of an experimental investigation of the flows generated by monodisperse particles settling at low Reynolds number in a stably stratified ambient with an inclined sidewall. In this configuration, upwelling beneath the inclined wall associated with the Boycott effect is opposed by the ambient density stratification. The evolution of the system is determined by the relative magnitudes of the container depth, h, and the neutral buoyancy height, h n = c 0 (ρ p − ρ f )/|dρ/dz|, where c 0 is the particle concentration, ρ p the particle density, ρ f the mean fluid density and dρ/dz < 0 the stable ambient stratification. For sufficiently weak stratification, h < h n , the Boycott layer transports dense fluid from the bottom to the top of the system; subsequently, the upper clear layer of dense saline fluid is mixed by convection. For sufficiently strong stratification, h > h n , layering occurs. The lowermost layer is created by clear fluid transported from the base to its neutral buoyancy height, and has a vertical extent h n ; subsequently, smaller overlying layers develop. Within each layer, convection erodes the initially linear density gradient, generating a step-like density profile throughout the system that persists after all the particles have settled. Particles are transported across the discrete density jumps between layers by plumes of particle-laden fluid.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

The stratified Boycott effect

2005

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“…Some aspects of heating a stable salinity gradient from the side have been considered previously by Thorpe, Hutt & Soulsby (1969), Chen, Briggs & Wirtz (1971), Wirtz, Briggs & Chen (1972) and Chen (1 974).t These investigations were primarily concerned with the onset of motion at low Rayleigh numbers. The work of Thorpe et al was further restricted in that most of the experiments and all of the theory were carried out for the case when the fluid is confined by a narrow slot.…”

Section: Horizontal Temperature Differencesmentioning

confidence: 96%

Ice blocks melting into a salinity gradient

1980

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I n our previous qualitative paper, it was shown that when a vertical ice surface melts into a stable salinity gradient, the melt water spreads out into the interior in a series of nearly horizontal layers. The experiments reported here are aimed a t quantifying this effect, which could be of some importance in the application to melting icebergs. Experiments have also been carried out with heated and cooled vertical walls a t larger Rayleigh numbers R than those of previous experiments.The main result is that for most of our experiments there is no significant difference between these three cases when properly scaled. The layer thickness over a wide range of R is described to within the experimental accuracy by where the term in brackets is the horizontal buoyancy difference evaluated a t the mean salinity and dpldz is the vertical density gradient due to salinity. I n the case of ice melting into warm water the effective wall temperature T, is approximately 0 "C, whereas in colder water the freezing point depression must be taken explicitly into account. A detailed examination of the vertically flowing inner melt water layer in both homogeneous and salinity stratified cases has been made. This layer and the melt water which is mixed outwards from it into the turbulent horizontal layers have little effect on the outer flow. At high R and large external salinity, however, mixing can reduce the effective salinity a t the inner edge of the horizontal layers, and thus the layer scale. A puzzling feature is the relatively weak dependence of layer scale on local salinity, though the vigour of convection and the rate of melting are greater where the salinity is high.The direct application of our results to oceanographic situations predicts layer scales under typical summer conditions of order tens of metres in the Antarctic and of order metres in the Arctic. More measurements will be needed, especially close to icebergs, before the application of these ideas to polar regions can be properly evaluated.

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“…Several types 'of laboratory experiments have been performed which investigate the stability of a system with lateral thermohaline gradients (Thorpe, et al, 1969, Turner and Chen, 1974, Linden and Weber, 1976, Turner, 1978 Sections, T/S diagrams and synoptic maps will be used to study the large scale field. ,Vertical motions, primarily internal waves on the time scale of interest here, greatly distort the interleaving field.…”

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confidence: 99%

Wintertime convection and frontal interleaving in the Southern Ocean

Toole¹

1980

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The Southern Ocean as defined here is the body of water between the Antarctic Continent and the Antarctic Polar Front, (APF).This ocean is considered important in the global thermodynamic balance of the ocean-atmosphere system because large planetary heat losses are believed to occur at high latitudes.The ocean and atmosphere must transport heat poleward to balance these losses.In the Southern Hemisphere, the oceanic contribution to this flux involves a southward transport of heat across the APF into the Southern Ocean where it is given up to the atmosphere through air-sea interactions.In Part I, the air-sea interactions and structure of the' near surface waters of the Southern Ocean are investigated with a three dimensional time dependent numerical model.The surface waters in this region in summer are characterized by a relatively warm surface mixed layer with low salinity.Below this layer, a cold temperature extremum is usually observed in vertical profiles which is believed to be the remnant of a deep surface mixed layer produced in winter.The characteristics of this layer, the surface mixed layer and the observed distribution of wintertime sea ice are reproduced well by this model.Unlike some other sea-ice models the air-sea heat exchange is a free variable.Model estimates of the annual heat loss by the Southern Ocean exhibit the observed meridional variation of heat gained by the ocean along the APF with heat lost further south.The model's area average heat loss is much smaller than that estimated with direct observations. While several model parameterizations were made which could be in error, the model results suggest that the Southern Ocean does give up vast amounts of heat to the atmosphere away from the continental margins.The model results and direct calculations of air-sea exchanges suggest a southward heat flux must occur across the APF.The lateral water mass transition across the front is not discontinuous but occurs over a finite sized zone of fluid which is dominated by intrusive finestructure.The characteristics and dynamics of these features are investigated in Part II to try and assess their importance in the meridional heat budget. Abstract (Contd.)Observations made on two cruises to the APF are presented and the space-time scales of the features and thermohaline characteristics are discussed. It is suggested that double diffusive processes dominated by salt fingering are active within the intrusions.An extension of Stern's (1967) model of the stability of a thermohaline front to intrusive finestructure driven by saltfingering where-small scale viscous processes are included, is presented to explain why intrusions are observed in frontal zones.The model successfully predicts vertical scales of intrusions observed in the ocean and the observed dependence of the intrusions' slopes across density surfaces on the vertical scale.Since the fastest growing intrusion is not strongly determined by the model, though, it is likely that finite amplitude effects determine the dominant scale of int...

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The effect of horizontal gradients on thermohaline convection

Cited by 196 publications

References 9 publications

The stratified Boycott effect

The stratified Boycott effect

Ice blocks melting into a salinity gradient

Wintertime convection and frontal interleaving in the Southern Ocean

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