A numerical study of cloud streets in the planetary boundary layer

Mason, P. J.

doi:10.1007/bf00121884

Cited by 19 publications

(10 citation statements)

References 18 publications

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“…This simplification may be justified by the results of Mason (1985), who found the influence of latent heating on the roll dynamics to be negligible, although more recent results of Sykes et al (1988) indicate a possible impact of humidity on the roll aspect ratio. Because the predicted higher aspect ratios only appear (as in nature) a certain time after the first formation of clouds, the model simulations presented in this paper can be regarded as valid for the first stage of roll development, extending some 100 km off the coast.…”

Section: Description Of the Modelmentioning

confidence: 91%

“…The effects on roll development of latent heat release and nonprecipitating clouds with cloud-top cooling are still discussed differently. Mason (1985) did not find any substantial changes in roll dynamics considering simulations with and without these effects; however. simulations of Sykes et al (1988) with a similar model led to aspect ratios (ratio of wavelength to height of the rolls) up to 10 when including latent heat effects compared to aspect ratios of only 4 in cases without moisture.…”

Section: Introductionmentioning

confidence: 87%

“…With the assumption of a Mason, 1985), regions of downward motions are not so well-developed, with the vertical velocity seldom exceeding values of 1 .O m SK'. For reasons of continuity, this indicates that the regions of downward motion must cover a greater area, compared to the updraft zones, which can be seen in Figure la-c.…”

Section: Simulation Of An Ideal Cold Air Outbreak and Comparison Withmentioning

confidence: 99%

“…Some authors, who performed model runs in order to compare results with observed values, had some problems in determining realistic boundary conditions. Mason (1985) stated that 'over the sea a specific surface temperature is a more physically realistic boundary condition but it was difficult to specify values leading to the observed heat flux', but did not give an explanation for these difficulties. Instead, he used a fixed surface heat flux for his simulations of KonTur observations.…”

Section: Introductionmentioning

confidence: 99%

“…In previous simulations of CAOs, where the roll-scale has been resolved by the numerical grids used, either quasi-stationary conditions have been considered (Mason, 1985;Chlond, 1988) or computations have been performed under unsteady conditions, which however could not be compared with observations directly, because idealized initial and boundary conditions (like the fixed heat flux in Sykes ef al., 1988) were prescribed. Therefore, the intention of this paper is to simulate the temporal development of the CBL during a CAO, resolving roll-scale motions with the aid of a 2D-model and using observed initial and boundary conditions.…”

Section: Introductionmentioning

confidence: 99%

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Numerical simulation of the development of the convective boundary layer during a cold air outbreak

Raasch

1990

Boundary-Layer Meteorol

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During cold air outbreaks, cold and stably stratified air masses are advected from land or ice surfaces over a warmer sea surface. Due to the heating from below, a convective boundary layer develops. For small fetches, convection is organized in the form of horizontal roll vortices, which at greater distances join in a zone with open or closed cells. The formation of the convective boundary layer, and the associated roll vortices, is simulated with a numerical model and results are compared with observations obtained during the MASEX experiment off the east coast of the United States. To validate the model, a comparison with a one-dimensional mixed-layer model is also made. with special attention given to the exact representation of the observed initial and boundary conditions. Comparisons between model results and observations show good qualitative and quantitative correspondence in mean temperature and heat flux profiles respectively at different distances from the coast. Maximum values of vertical velocity are well reproduced. Turbulent kinetic energy is found to be concentrated in the small updraft regions of the rolls, which is in accordance with observations from the MASEX-experiment.

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Section: Description Of the Modelmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 87%

Section: Simulation Of An Ideal Cold Air Outbreak and Comparison Withmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Numerical simulation of the development of the convective boundary layer during a cold air outbreak

Raasch

1990

Boundary-Layer Meteorol

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Diurnal Variations In Flow Over A Succession of Ridges and Valleys

Mason

1987

Quart J Royal Meteoro Soc

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Observations of flow in a nearly two-dimensional valley located within a succession of similar ridges and valleys are presented. Measurements of the mean flow have been made at all times of the day and are found to be well characterized by a suitably defined Froude number. The unstable and neutral daytime flow shows a flow separation whilst when the Froude number has a value of about two (usually around evening and dawn transitions) the flow is attached and the valley well ventilated. For smaller values of Froude number the flow speed in the valley reduces and a characteristic 'drainage' flow occurs.In addition to mean flow measurements and soundings of temperature structure, measurements were also made of turbulence energy and stress. This allows an estimate of the effective value of the surface roughness, z, , and an indication of the stability dependence of the momentum transfer to be made.

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Dynamical analyses of marine atmospheric boundary layer structure near the Gulf Stream oceanic front

Wai

Stage

1989

Quart J Royal Meteoro Soc

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The effects of the sea surface temperature (s.s.t.) front at the edge of the Gulf Stream on the marine atmospheric boundary layer (MABL) are investigated using a numerical model to study the modification effects of an oceanic front on the MABL structure. The situation simulated is flow from over cold shelf water to over the warm water of the Gulf Stream. The initial temperature and humidity profiles of the air are specified to be near neutral over the cold water and are therefore typical of undisturbed conditions. The differential in s.s.t. across the oceanic front creates a horizontal variation in the surface perturbation pressure and the stability. The surface perturbation pressure and turbulent fluxes modulate the flow and produce horizontal variations in horizontal wind components with associated vertical motions. A thermally direct cell is produced as a result of the s.s.t. difference across the front. The isotherms slope upward towards the warm water. Entrainment of inversion layer air and upward vertical motion over the warm water cause the MABL to be deeper there. A layer of cloud forms over warm water and is associated with mixed layer deepening rather than lowering of the condensation level. Turbulent fluxes in the MABL show considerable spatial variation. Surface stress is much larger over the front and over the warm water than over the cold water. This is mostly caused by wind speed changes associated with the front. Changes in the drag coefficient due to changes in surface roughness and stability are much less important.Mean budgets for temperature and total water indicate that there is a balance between horizontal advection and turbulent flux divergence. The U momentum budget shows that once the geostrophic balance terms are subtracted, the balance is mainly between the pressure gradient force associated with the induced temperature field and turbulent friction, with horizontal advection and the Coriolis force acting on the geostrophic departure playing minor roles. The V momentum budget shows a balance between horizontal advection, Coriolis force and friction.Although there are few data for comparison, the results are in qualitative agreement with observations in the area. This study shows that the s.s.t. front at the Gulf Stream edge produces marked local changes in the nearby atmospheric surface layer. 29

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A numerical study of cloud streets in the planetary boundary layer

Cited by 19 publications

References 18 publications

Numerical simulation of the development of the convective boundary layer during a cold air outbreak

Numerical simulation of the development of the convective boundary layer during a cold air outbreak

Diurnal Variations In Flow Over A Succession of Ridges and Valleys

Dynamical analyses of marine atmospheric boundary layer structure near the Gulf Stream oceanic front

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