Some problems of closure assumption and scale dependency in the parameterization of moist deep convection for numerical weather prediction

Bougeault, Ph.; Geleyn, Jean-François

doi:10.1007/bf01027471

Cited by 22 publications

(17 citation statements)

References 13 publications

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“…The ADC concept has since been largely used in the literature. This parameterization of the diffusion process by a global ADC is similar to the step followed by meteorologists to describe atmospheric processes on a scale (parcel) that is large when compared with that of the local physical processes [14]. Parameterization is intended to represent physical processes that occur on scales smaller than those resolved by the method-the large scale is imposed by technical limitations (for example, large distances between weather measurement stations), whereas the actual dtheatreT scale of the physical In the presence of a spatially varying magnetic field (induced through a magnetic field gradient, the amplitude and timing of which are characterized by a dbT factor), moving molecules emit radiofrequency signals with slightly different phases.…”

Section: Diffusion and Tissue Microstructure: A Scaling Issuementioning

confidence: 98%

Looking into the functional architecture of the brain with diffusion MRI

Bihan

2006

International Congress Series

420

531

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Section: Diffusion and Tissue Microstructure: A Scaling Issuementioning

confidence: 98%

Looking into the functional architecture of the brain with diffusion MRI

Bihan

2006

International Congress Series

420

531

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“…It has been reported that, when a parameterized convective scheme is incorporated into a mesoscale model, the simulated precipitation increases as the grid size decreases (e.g., Bougeault and Geleyn, 1989). This increase is presumably induced by the use of both the hydrostatic approximation and the precipitation scheme.…”

Section: Introductionmentioning

confidence: 99%

Hydrostatic and Non-Hydrostatic Simulations of Moist Convection

Kato¹,

Saitō²

1995

Journal of the Meteorological Society of Japan

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Comparative experiments of moist convection using hydrostatic and non-hydrostatic models are performed to study the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20km. The moist convection in the models is treated by the use of an explicit warmrain process predicting cloud water and rainwater as well as by a semi-explicit scheme consisting of the warm-rain process and moist convective adjustment. The differences between the experiments with and without hydrostatic water loading are also examined and quantitatively compared with those between the hydrostatic and non-hydrostatic simulations.When the prognostic explicit scheme is used, the hydrostatic simulation overdevelops moist convection, overestimates the total amount of precipitation, and overexpands the area of precipitation as the grid size decreases. This overdevelopment alters substantially the structure of moist convection and precipitation patterns. The absence of hydrostatic water loading also alters the total amount and structure of precipitation. Hydrostatic water loading exerts more significant influences on simulated precipitation than the hydrostatic approximation. In the 20-km simulations, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the non-hydrostatic counterpart.The difference in the total amount of precipitation between the hydrostatic and non-hydrostatic simulations was not as large as that of the convective development. This can be explained by considering the total water budget, which includes simulated precipitation and water vapor flux through the lateral boundaries, i, e., the water-vapor flux in the hydrostatic simulation corresponds to that in the non-hydrostatic one.Although moist convective adjustment removes conditional instability and does not produce strong updrafts, the characteristics of the results in the comparative experiments of moist convection using hydrostatic and non-hydrostatic models were hardly changed by the incorporation of moist convective adjustment (the semi-explicit scheme). On the other hand, hydrostatic water loading exerts more significant influences on simulated precipitation with the semi-explicit scheme than that with the prognostic explicit scheme. Therefore, in developing 10-20km numerical weather prediction models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models.

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“…Therefore, we apply a deep convection scheme, namely a modified Bougeault (1985) scheme, in our ALADIN simulations. This scheme and its pros and cons in very high resolution modeling are discussed in Bougeault and Geleyn (1989) and Gerard (2001). Important aspects of the implementation of the modified Bougeault-scheme are (a) the utilization of large-scale precipitation and deepconvection scheme at the same grid points, (b) the reduction of large-scale moisture-convergence provided to the deepconvection scheme depending on mesh size and vertical convergence of the large-scale precipitation flux and (c) the affection of the large-scale through detrainment of cloud variables to the environment, and thus establishing a feed back mechanism.…”

Section: Aladin Configurationsmentioning

confidence: 99%

On ALADIN precipitation modeling and validation in an Alpine watershed

Ahrens

Jasper²,

Gurtz³

2003

Ann. Geophys.

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Abstract. Highly resolved precipitation forecasts are necessary in many applications, especially in mountain meteorology and flash flood forecasts for small-to medium-sized alpine watersheds. Here we present precipitation forecasts simulated by the limited area model ALADIN applying different grid resolutions ( x = 10 km and 4 km). Target area of the investigations is the Alpine Ticino-Verzasca-Maggia watershed (total area: 2627 km 2 ).We discuss problems of validation of high-resolution precipitation forecasts by comparison with observed precipitation fields and apply an indirect validation approach by using ALADIN forecasts as input to hydrologic simulations. These simulations are carried out with the distributed hydrologic model WaSiM-ETH ( x = 500 m, t = 1 h). The time step of meteorological input to WaSiM-ETH is fixed at 1 h but spatial resolution varies.The main result of the validation experiments for three heavy precipitation events is, that coarser-scale ALADIN forecasts (in model version 11.2) provide better precipitation predictors for hydrologic modeling than higher-resolution forecasts. The experiments demonstrate that hydrologic modeling is a promising tool for the evaluation of highresolution precipitation fields.

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Some problems of closure assumption and scale dependency in the parameterization of moist deep convection for numerical weather prediction

Cited by 22 publications

References 13 publications

Looking into the functional architecture of the brain with diffusion MRI

Looking into the functional architecture of the brain with diffusion MRI

Hydrostatic and Non-Hydrostatic Simulations of Moist Convection

On ALADIN precipitation modeling and validation in an Alpine watershed

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