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  • 1
    Electronic Resource
    Electronic Resource
    Mesoscale observations of surface fronts and low pressure centres in Canadian East Coast winter storms (1993)
    Springer
    Boundary layer meteorology 64 (1993), S. 15-54 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The movements of surface cold and warm fronts and low pressure centres have been observed in several Atlantic Canada winter storms. Statistical aspects of the ‘well-defined’ surface fronts (7 warm and 6 cold) are presented. Surface wind direction change was considered as the best indicator of the boundaries of the front; frontal zone widths ranged from 23 to 144 km. Average values of wind shifts were 107° for the cold fronts and 85° for warm fronts. Several case studies are presented, based primarily on surface MesoNet data (near Halifax, Nova Scotia and on Sable Island). In two of the cold fronts, there was a two-stage surface structure and rapid evolution as the front passed over the MesoNet. In some cases, both warm and cold, the wind shift and temperature change were coincident while in others they were not. In particular we observed that wind shifts often started 20–30 min ahead of the start of a temperature decrease in these cold frontal passages. A possible mechanism for this is discussed. We found little or no evidence of along-front structure in our data although other investigators have found considerable along-front variation on scales of 0(10 km). Observations of the passage of one low pressure centre are presented. In a second case, surface temperature changes indicated an apparent low pressure centre passage through the Sable Island MesoNet but closer inspection provides an alternative interpretation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705661
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  • 2
    Electronic Resource
    Electronic Resource
    A non-linear extension of the mixed spectral finite difference model for neutrally stratified turbulent flow over topography (1992)
    Springer
    Boundary layer meteorology 59 (1992), S. 177-186 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A non-linear extension of the mixed spectral finite difference model for neutrally stratified surface-layer flow over complex terrain is developed. The non-linear terms are treated as additional source terms in the present model. The solution is calculated iteratively in spectral space, while the source terms are evaluated in physical space (at each iteration step) with the help of a Fast Fourier Transform algorithm. Results for simple 2D sinusoidal topography are shown to compare well with full non-linear finite difference results. The method, compared to conventional finite difference methods, has the advantage of rapid convergence and substantial savings in computer time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120693
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The impact of turbulence closure schemes on predictions of the Mixed Spectral Finite-Difference model for flow over topography (1994)
    Springer
    Boundary layer meteorology 68 (1994), S. 1-33 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Impacts of different closure schemes in the Mixed Spectral Finite-Difference model (Beljaarset al., 1987) for neutrally stratified atmospheric surface-layer flow over complex terrain are studied. Six different closure schemes, κ(Z+z 0), Mixing Length,E−κ(Z+z 0),E−ε,E−ε−π andq 2 l are compared. Model results for flow over an infinite series of sinusoidal ridges are examined in the context of the inner and outer layers defined by Jackson and Hunt (1975). Results are compared with rapid distortion estimates of the changes in normal stresses. The effects of streamline curvature are also examined in a qualitative sense.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712662
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On gas fluxes from small lakes and ponds (1994)
    Springer
    Boundary layer meteorology 68 (1994), S. 339-356 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A semi-empirical model for estimating gas fluxes at the air-water interface in a neutrally stratified atmosphere is presented. Gas transfer velocity is assumed to depend on local friction velocity, whose variation with over-water fetch is estimated from Walmsleyet al.'s (1989) ‘Guidelines’. As guidance for limnologists estimating CO2 and CH4 fluxes from lakes and ponds in the Hudson Bay Lowlands region, we present model results of the variation of gas transfer velocity with over-water fetch,k(x), for comparison with the customary constant valuek 0. Gas fluxes are estimated over well mixed, circular and elliptical lakes and ponds. The results of accounting for fetch dependence, wind direction, pond shapes and sizes lead to correction factors to fluxes obtained withk 0. Recent studies of gas transfer velocity for gases of low solubility from lakes are reviewed, and the problem of time averaging on quantities determined from experimental measurements is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00706795
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  • 5
    Electronic Resource
    Electronic Resource
    Development of a non-linear mixed spectral finite difference model for turbulent boundary-layer flow over topography (1994)
    Springer
    Boundary layer meteorology 70 (1994), S. 341-367 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Further development of the non-linear mixed spectral finite difference (NLMSFD) model of turbulent boundary-layer flow over topography is documented. This includes modifications and refinements to the solution procedure, the incorporation of second-order turbulence closures to the model and the three-dimensional extension of the model. Based on these higher order closures, linear limitations, boundary-layer approximation and non-linear effects are discussed. The impact of different turbulence closures on the prediction of the NLMSFD model is also demonstrated. Furthermore, sample results for 3D idealized topography (sinusoidal) are presented. The parameterization of drag over small-scale topography is also addressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713775
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  • 6
    Electronic Resource
    Electronic Resource
    A note on the constants used inE-ɛ-τ turbulence closure (1995)
    Springer
    Boundary layer meteorology 72 (1995), S. 205-211 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712395
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Fronts and the boundary layer – some numerical studies (1998)
    Springer
    Boundary layer meteorology 89 (1998), S. 469-506 
    Details
    ISSN: 1573-1472
    Keywords: Boundary layer ; Fronts ; Numerical model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this paper, we consider boundary-layer effects on atmospheric fronts. For this purpose we developed a dry, hydrostatic, two-dimensional numerical model with turbulence parameterized with the 1/2 -order eddy viscosity closure of Mellor and Yamada. In the surface layer we use Monin–Obukhov similarity and there is an interactive soil model to obtain lower boundary conditions for the atmospheric model. First, effects of turbulence are studied without thermal forcing at the surface and comparisons are made between inviscid and turbulent conditions. Sensitivity studies with respect to surface roughness are also performed. Subsequently we study effects of surface thermal forcing on fronts. The results show that, during summer, fronts display strong diurnal variation. Vertical velocities increase significantly during the day while gradients in temperature and vorticity across the front strengthen in the evening and at night. In winter the diurnal variation is much less pronounced. We attempt to find physical mechanisms responsible for such frontal behaviour and we compare our results with available observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001750420805
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  • 8
    Electronic Resource
    Electronic Resource
    Comments and further analysis on effective roughness lengths for use in numerical three-dimensional models (1987)
    Springer
    Boundary layer meteorology 39 (1987), S. 403-418 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Simple calculations of the apparent roughness length for the areally averaged flow over flat but heterogeneous terrain are presented. These results could be used to specify effective roughness lengths for use in large-scale models. Some of our conclusions differ significantly from those reached recently by André and Blondin (1986).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125144
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  • 9
    Electronic Resource
    Electronic Resource
    On the parameterization of drag over small-scale topography in neutrally-stratified boundary-layer flow (1989)
    Springer
    Boundary layer meteorology 48 (1989), S. 409-422 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Predictions of the surface drag in turbulent boundary-layer flow over two-dimensional sinusoidal topography from various numerical models are compared. For simple 2D terrain, the model results show that the drag increases associated with topography are essentially proportional to (slope)2 up to the steepness at which the flow separates. For the purposes of boundary-layer parameterisation within larger-scale models, we propose a representation of the effects of simple 2D topography via an effective roughness length, z 0 eff. The form of the varation of z 0 eff with terrain slope and topographic wavelength is established for small slopes from the model results and a semi-empirical formula is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123062
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  • 10
    Electronic Resource
    Electronic Resource
    On the inner-layer scale height of boundary-layer flow over low hills (1989)
    Springer
    Boundary layer meteorology 49 (1989), S. 433-438 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The scaling properties of the depth of the inner-layer of flow over low hills are studied by means of numerical solution of the equations. Two closure schemes are applied: the mixing-length model and the E-ε formulation. It is shown that the scale relation for the inner-layer depth lies between two formulations proposed in literature. It is also shown that the scale relation depends on the closure scheme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123654
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    Paper (German National Licenses)
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