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Alan K. Betts

Abstract

One-dimensional thermodynamic models for cloud-environment mixing, evaporation into downdrafts and precipitation from updrafts are presented in a parallel treatment using convective pressure scales and saturation point coordinates. This common framework can be used to interpret data sets and estimate from them pressure scales for the complex physical processes in cumulus.

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Alan K. Betts

Abstract

A vector representation of the BOMEX thermodynamic budget data is presented which shows graphically the relationship of the fluxes and the mean layer structure.

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Alan K. Betts

Abstract

A one-dimensional cumulus model is used to interrelate cloud radius, stratification and cloud height. It is suggested that if only certain ranges of cloud height and radius are permitted, then from the stratification, one can predict, using a model, allowed cloud radii and a corresponding depth to the convective layer.

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Alan K. Betts

Abstract

A lagged mixing parameterization is proposed for the dry convective boundary layer in which the entrainment rate is controlled by the adjustment time chosen. Data from a growing boundary layer over land are used as illustration.

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Alan K. Betts

Abstract

This paper interprets the diagnostic budget studies of the undisturbed BOMEX period, 22-26 June 1969, using a parametric cloud model with continuous detrainment as well as entrainment. Compensating environmental motion, lateral detrainment and cloud transience are discussed in relation to the model results. The model shows the close coupling of the thermodynamic fluxes, and suggests that they can be represented well for some purposes, by a single cloud mass flux profile, rather than by a spectral cloud model. The extension of the methodology to precipitating convection is indicated briefly.

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Alan K. Betts

Abstract

The diagnostic study of the thermodynamic structure of nonprecipitating clouds and cloudy boundary layers is formulated using a mixing line and saturation point approach. A parametric model for the mean structure is developed as a tool for diagnostic and prognostic modeling. Cloud-scale mixing process are analyzed in the same framework, together with the energetics of the evaporative instability in cumulus clouds. A velocity scale emerges for this evaporative instability. The statistical study of saturation level distribution in partially cloudy boundary layers is proposed to related cloud fraction to the mean thermodynamic mixing processes.

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Alan K. Betts

Abstract

No abstract available.

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Alan K. Betts

Abstract

This paper couples a mixed subecloud layer model developed by several authors with the cumulus flux parameterization proposed by Betts (1975). Cloud base mass flux and mass flux gradient are related to sub-cloud layer parameters and cumulus layer gradients using two parameters, α and β. The α symbol is the ratio of a model transition layer depth to the subcloud layer depth, and β is the ratio of a model cloud base static energy flux to the surface flux. For the simple case of a steady-state transition layer, the subecloud layer beat and moisture budgets are predicted.

Data from a field experiment over Venezuela are used to illustrate mean subcloud layer structure and to derive heat and moisture flux profiles and model parameters from a simple budget analysis. The data give (α,δ)=(0.11, 0.41) and correspondingly, (αv1βv based on virtual static energy fluxes and profiles. During the budget time period (centered on local noon over land) the subeloud layer war and dries with a corresponding rise of cloud base. The steady-state transition layer model predictions showed qualitative agreement with the fluxes derived from the budget. The extension of the convective mass flux model into the subeloud layer was shown to be feasible. It illustrates the rapid decrease of convective mass flux across the transition layer.

The paper concludes that the model is a satisfactory diagnostic tool for subcloud layer budgets and the cloud-subdoud layer interaction, and may have predictive value.

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Alan K. Betts

Abstract

The transformation by precipitation of the well-mixed subcloud layer into a new structure which is nearly wet adiabatic and has a lower moist static energy is presented. A simple two-layer model is used to show that the precipitating convection appears to strip off the subcloud layer which ascends in updrafts, and to replace it with an equal layer of air from just above cloud base, which descends in downdrafts associated with the evaporation of falling rain. The mean transformation is presented, and the incorporation of the results into a parametric model of the transformation of the subcloud layer is discussed.

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Alan K. Betts

Abstract

A unified approach to the thermodynamics of cloudy air, cloud-clear air mixing processes, atmospheric thermodynamic equilibrium structure and instability is formulated, using a new concept: the Saturation Point. This permits the representation of mixing processes and virtual potential temperature isopleths for clear and cloudy air on a thermodynamic diagram (a tephigram is used here), and their comparison with the atmospheric stratification. Illustrative examples will be given for evaporative mixing instability and convective equilibrium structure for stratocumulus, cumulus and cumulonimbus convection and convection in the incipient severe storm atmosphere.

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