Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Stratified Atmospheric Boundary Layers and Breakdown of Models (1998)
    Springer
    Theoretical and computational fluid dynamics 11 (1998), S. 263-279 
    Details
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract: The goal of this study is to assess complications in atmospheric stable boundary layers which are not included in numerical models of the stably stratified boundary layer and to provide a formulation of surface fluxes for use in numerical models. Based on an extensive interpretive literature survey and new eddy correlation data for the stable boundary layer, this study defines two prototype stable boundary layers: the weakly stable case and the very stable case. The weakly stable boundary layer is amenable to existing models. The very stable boundary layer eludes modeling attempts due to breakdown of existing formulations of turbulence and due to features found in the atmosphere which are not normally included in models. The latter includes clear-air radiative cooling, low-level jets, surface heterogeneity, gravity waves, meandering motions, and other mesoscale motions which propagate from outside the local domain. While these mechanisms are not essential to understanding idealized or laboratory versions of the stable boundary layer, they complicate comparisons of numerical models and theories with actual atmospheric boundary layers. Statistics which describe various features of the stable boundary layer are offered for future comparison with modeling results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001620050093
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    A two-scale mixing formulation for the atmospheric boundary layer (1995)
    Springer
    Boundary layer meteorology 73 (1995), S. 91-104 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This study compares different simple mixing schemes for one-dimensional models and then focuses on the two-scale mixing approach. Two-scale mixing consists of local diffusion between adjacent grid levels and nonlocal mixing over the bulk of the boundary layer (nonlocal mixing). The latter represents nonlocal mixing by the boundary-layer scale eddies. A common example of two-scale mixing is the formulation of the turbulent heat transport in terms of an eddy diffusivity to represent small-scale diffusion and a “countergradient correction” to represent boundary-layer scale transport. Most existing two-scale approaches are applied to heat and moisture transport while momentum transport is simultaneously parameterized only in terms of a local diffusivity without nonlocal mixing. This study attempts to correct this inconsistency. The resulting model is compared with Lidar observations of spatially averaged winds which are found to be superior to radiosonde and aircraft data for determining the mean structure. The two-scale mixing correctly predicts the observed well mixed conditions for momentum while the original model based on a local diffusivity for momentum fails to produce a well mixed state. Unfortunately, the “best” value for the adjustable coefficient in the nonlocal mixing part of the two-scale approach appears to depend on baroclinity in a way which can not be completely resolved from existing data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708931
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Stratified Atmospheric Boundary Layers (1999)
    Springer
    Boundary layer meteorology 90 (1999), S. 375-396 
    Details
    ISSN: 1573-1472
    Keywords: Intermittent turbulence ; Monin–Obukhov ; Nocturnal boundary layer ; Stable boundary layer ; Surface layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet, gravity waves or meandering motions. In this case, similarity theory and the traditional concept of a boundary-layer break down. The elevated turbulence may intermittently recouple to the surface. Inability to adequately measure turbulent fluxes in very stable conditions limits our knowledge of this regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001765727956
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Nocturnal Boundary-Layer Regimes (1998)
    Springer
    Boundary layer meteorology 88 (1998), S. 255-278 
    Details
    ISSN: 1573-1472
    Keywords: Meandering ; Monin-Obukhov theory ; Nocturnal boundary layer ; Obukhov length ; Stable boundary layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This study analyzes turbulence data collected over a grassland site in the nocturnal boundary layer. Examination of the dependence of the nocturnal boundary layer on stability suggests three regimes: a) the weakly stable case, b) a transition stability regime where many of the variables change rapidly with increasing stability and c) the very stable case. The value of z/L where the downward heat flux is a maximum defines the stability boundary between the weakly stable and transition regimes, where L is the Obukhov length. In the present analysis, the downward heat flux reaches a maximum at z/L approximately equal to 0.05 for 10 m, although comparison with other data indicates that this is not a universal value. For weaker stability, the heat flux decreases with decreasing z/L due to weaker temperature fluctuations. In the transition stability regime, the heat flux decreases rapidly with increasing stability due to restriction of vertical velocity fluctuations by the increasing stratification. For weakly stable conditions, the variances scale according to Monin-Obukhov similarity theory. For very stable conditions, the variances are contaminated by non-turbulent horizontal motions and do not follow the scaling laws. An alternative length scale based on variances is developed which explains more of the variance of the transfer coefficients compared to the Obukhov length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001171313493
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Relationship of surface heat flux to microscale temperature variations: Application to boreas (1995)
    Springer
    Boundary layer meteorology 76 (1995), S. 291-301 
    Details
    ISSN: 1573-1472
    Keywords: Heat flux ; Forest meteorology ; Microscale ; Surface radiation temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The surface heat flux is normally parameterized in terms of the difference between the air temperature and the surface radiative temperature, or equivalently, the temperature computed from the surface energy balance. In this note, the relationship between the heat flux and the air-surface temperature difference is shown to be sensitive to the microscale variability of the surface radiation temperature caused by differences between the well-ventilated tree tops and less ventilated ground surface. This conclusion is based on surface and aircraft data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS). For this case, the heat flux cannot be predicted by adjusting the thermal roughness height. As an alternative, the aerodynamic temperature can be related to a weighted average of the surface radtation temperature analogous to application of a simple canopy model. Here, the total heat flux is the sum of the heat fluxes from each individual surface type weighted by the area-fractional coverage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00709355
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Multiresolution Flux Decomposition (1997)
    Springer
    Boundary layer meteorology 83 (1997), S. 117-137 
    Details
    ISSN: 1573-1472
    Keywords: Reynolds averaging ; Turbulence ; Time series ; Cospectra ; Sampling error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Geophysical variables are orthogonally decomposed by averaging timeseries using different averaging lengths, referred to as a (Haar)multiresolution decomposition. This simple and economic decomposition isassociated with cospectra that formally satisfy Reynolds averaging rules foreach averaging length. The multiresolution decomposition provides a naturalestimate of the random error in estimating a mean turbulent flux. The Fourierand multiresolution decompositions are compared using aircraft data fromBOREAS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000210427798
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Fetch Limited Drag Coefficients (1997)
    Springer
    Boundary layer meteorology 85 (1997), S. 53-79 
    Details
    ISSN: 1573-1472
    Keywords: Surface drag ; Drag laws ; Sea surface stress ; Wave age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Measurements made at a tower located 2 km off the coast of Denmark inshallow water during the Risø Air Sea Experiment (RASEX) are analyzedto investigate the behaviour of the drag coefficient in the coastal zone.For a given wind speed, the drag coefficient is larger during conditions ofshort fetch (2-5 km) off-shore flow with younger growing waves than it isfor longer fetch (15-25 km) on-shore flow. For the strongest on-shorewinds, wave breaking enhances the drag coefficient. Variation of the neutral drag coefficient in RASEX is dominated byvariation of wave age, frequency bandwidth of the wave spectra and windspeed. The frequency bandwidth is proportional to the broadness of the waveheight spectra and is largest during conditions of light wind speeds. Usingthe RASEX data, simple models of the drag coefficient and roughness length are developed in terms of wind speed, wave age and bandwidth. An off-shoreflow model of the drag coefficient in terms of nondimensional fetch isdeveloped for situations when the wave state is not known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000472623187
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    The bulk aerodynamic formulation over heterogeneous surfaces (1996)
    Springer
    Boundary layer meteorology 78 (1996), S. 87-119 
    Details
    ISSN: 1573-1472
    Keywords: Bulk aerodynamic formulation ; Drag law ; Heat flux ; Surface fluxes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This interpretative literature survey examines problems with application of the bulk aerodynamic method to spatially averaged fluxes over heterogeneous surfaces. This task is approached by tying together concepts from a diverse range of recent studies on subgrid parameterization, the roughness sublayer, the roll of large “inactive” boundary-layer eddies, internal boundary-layer growth, the equilibrium sublayer, footprint theory and the blending height. Although these concepts are not completely compatible, qualitative scaling arguments based on these concepts lead to a tentative unified picture of the qualitative influence of surface heterogeneity for a wide spectrum of spatial scales. Generalization of the velocity scale is considered to account for nonvanishing heat and moisture fluxes in the limit of vanishing time-averaged wind speed and to account for the influence of subgrid mesoscale motions on the grid-averaged turbulent flux. The bulk aerodynamic relationship for the heat flux usually employs the surface radiation temperature or, equivalently, the temperature from the modelled surface energy budget. The corresponding thermal roughness length is quite variable and its dependence on available parameters is predictable only in special cases. An effective transfer coefficient to relate the spatially averaged surface fluxes to spatially averaged air-ground differences of temperature and other scalars can be most clearly defined when the blending height occurs below the reference level (observational level or first model level). This condition is satisfied only for surface heterogeneity occurring over horizontal scales up to a few times the boundary-layer depth, depending on the stability and height of the reference level. For surface heterogeneity on larger scales (small mesoscale), an effective transfer coefficient for the spatially averaged flow must be defined, for which predictive schemes are unavailable. For surface variations on large mesoscales, homogeneous subareas may be maintained where traditional similarity theory is locally applicable. Surface variations on these scales may generate thermally-driven mesoscale motions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122488
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Heat Flux in the Coastal Zone (1998)
    Springer
    Boundary layer meteorology 86 (1998), S. 421-446 
    Details
    ISSN: 1573-1472
    Keywords: Surface heat flux ; Sea surface fluxes ; Marine boundary layer ; Monin–Obukhov similarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Various difficulties with application of Monin–Obukhov similarity theory are surveyed including the influence of growing waves, advection and internal boundary-layer development. These complications are normally important with offshore flow. The transfer coefficient for heat is computed from eddy correlation data taken at a mast two kilometres off the Danish coast in RASEX. For these coastal zone data, the thermal roughness length shows no well-defined relation to the momentum roughness length or roughness Reynolds number, in contrast to previous theories. The variation of the momentum roughness length is dominated by wave state. In contrast, the thermal roughness length shows significant dependence on wave state only for small values of wave age where the mixing is apparently enhanced by wave breaking. The development of thin internal boundary layers with offshore flow substantially reduces the heat transfer and thermal roughness length but has no obvious influence on momentum roughness length. A new formulation of the thermal roughness length based on the internal boundary-layer depth is calibrated to the RASEX data. For the very stable case, the turbulence is mainly detached from the surface and existing formulations do not apply. As an alternative to adjusting the thermal roughness length, the transfer coefficient is related directly to the stability and the internal boundary-layer depth. This avoids specification of roughness lengths resulting from the usual integration of the non-dimensional temperature function. The resulting stability function is simpler than previous ones and satisfies free convection similarity theory without introduction of the gustiness factor. The internal boundary layer also influences the moisture transfer coefficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000784219817
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...