An entraining jet model for cumulo-nimbus updraughts

Squires, P.; Turner, J. S.

doi:10.3402/tellusa.v14i4.9569

Cited by 77 publications

(32 citation statements)

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“…dz P Finally, we adopt the simple approximation that the saturation vapor pressure for water vapor is Figure 4c). However, in the calculations we present below, we find that in most situations, the column first becomes saturated at temperatures below 273 K. In principle, the liquid water can subsequently freeze as it continues cooling; however, the liquid water may support some supercooling before ice nucleates [Squires and Turner, 1962].…”

Section: (1 -N -Q• )Ulfl = (1 -No)uooeofto (•O)mentioning

confidence: 82%

“…This is because atmospheric moisture is mainly confined to the lower few kilometers of the atmosphere; thus, only a small fraction of the mass entrained into large eruption columns is moist, in contrast to small colu.nms in which all the entrained air may be moist. Moist atmospheric convection, driven by the release of latent heat as vapor is lifted upward and becomes saturated and condenses, can produce updrafts which ascend 7-8 km in the troposphere [Morton, 1957;Squires and Turner, 1962].…”

Section: Copyright By the American C•ophysical Unionmentioning

confidence: 99%

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Moist convection and the injection of volcanic ash into the atmosphere

Woods¹

1993

J. Geophys. Res.

108

158

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If unsaturated water vapor is carried upward by a volcanic eruption column, it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air. Heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand. We show that this increases the buoyancy and therefore the total height of rise of the column. The increase in height is significant in relatively small sub‐Plinian and Strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg/s. In such eruptions, the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward. The height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere. In a moist atmosphere, ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment. Moist convection leads to much wider ash dispersal, particularly from very small eruptions. Subsequently, rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor; the ash provides natural condensation nuclei for some of this entrained vapor, whose mass may be much greater than that of the ash. In small columns (< 15km), the dominant source of water for the formation of accretionary lapilli may be derived from the entrained vapor. In larger Plinian eruptions (> 107 kg/s), the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics; furthermore, the mass of water vapor originating from the erupted volatiles is usually comparable to, or greater than, that entrained from the ambient air. Our model also shows that, if the erupting mixture becomes buoyant, then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as Plinian columns with the same mass eruption rate. This is because the water which is vaporized by the hot ash at the source, condenses higher in the column and thereby restores its latent heat to the ascending ash.

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Section: (1 -N -Q• )Ulfl = (1 -No)uooeofto (•O)mentioning

confidence: 82%

Section: Copyright By the American C•ophysical Unionmentioning

confidence: 99%

Moist convection and the injection of volcanic ash into the atmosphere

Woods¹

1993

J. Geophys. Res.

108

158

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“…Early attempts by Morton (1957), Squires and Turner (1962), and others to describe entrainment in cumulus clouds using a laterally entraining model, where air at a certain level comes solely from that level or below, failed to make realistic predictions in a cumulus cloud. Warner (1970) shows that the standard lateral entrainment model for plumes cannot simultaneously predict the height of ascent and air-water ratio in cumulus clouds.…”

Section: Introductionmentioning

confidence: 96%

A Conceptual Model for Entrainment in Cumulus Clouds

Agrawal

2005

Journal of the Atmospheric Sciences

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Cumulus clouds are generally modeled as a plume, and the model works well up until the cloud base is encountered, beyond which the continuously entraining model does not appear appropriate. Although it has been known for a long time that cumulus clouds have very little lateral entrainment, the reason for it is not evident. An expression for the mean streamwise velocity profile as a Gaussian multiplied by a fourth-order polynomial factor is hereby proposed such that the mass and momentum fluxes are decoupled. This model suggests that cumulus clouds differ from other shear flows in that the former need not interact with the ambient for some downstream distance. The proposed model replicates a number of characteristics of cumulus clouds like a conserved mass flux with varying momentum flux, and may therefore be employed to describe them, in a time-averaged sense, beyond the cloud base.

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“…Paper number 1999JD900034. 0148-0227 / 99 / 1999JD900034509.00 have so far been mainly directed toward the analysis of in-cloud measurements and the construction of numerical models whose predictions match the observations. One of the earliest such efforts was the laterally entraining plume model [Squires and Turner, 1962]. In this class of models, lateral entrainment is estimated employing a relationship of the type conceived first by G.I.…”

Section: Introductionmentioning

confidence: 99%

“…The entrained ambient fluid is assumed to mix instantaneously across the flow. Taylor's hypothesis has been successful in a variety of situations [see, e.g., Turner, 1986], but when applied to clouds, it has failed to make realistic predictions of either liquid water concentrations or height of penetration [•qquires and Turner, 1962;Warner, 1970]. Paluch [1979] showed that the observed thermodynamic properties in a cloud can be accounted for only if air from the cloud base rises to the top without lateral mixing with the surrounding air.…”

Section: Introductionmentioning

confidence: 99%