scholarly journals Characteristics of the Horizontal Wind Fluctuations in the Surface Layer under Strong Convective Conditions

1975 ◽  
Vol 53 (1) ◽  
pp. 99-102 ◽  
Author(s):  
Nobutaka Monji
Keyword(s):  
Surface Layer ◽  
Horizontal Wind ◽  
Convective Conditions

scholarly journals On the Formulation and Universality of Monin–Obukhov Similarity Functions for Mean Gradients and Standard Deviations in the Unstable Surface Layer: Results from Surface-Layer-Resolving Large-Eddy Simulations

2017 ◽  
Vol 74 (4) ◽  
pp. 989-1010 ◽  
Author(s):  
Björn Maronga ◽  
Joachim Reuder
Keyword(s):  
Surface Layer ◽  
Standard Deviation ◽  
Large Eddy Simulations ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
Convective Conditions ◽  
Similarity Functions ◽  
Large Eddy ◽  
The Mean ◽  
Standard Deviations

Abstract Surface-layer-resolving large-eddy simulations (LESs) of free-convective to near-neutral boundary layers are used to study Monin–Obukhov similarity theory (MOST) functions. The LES dataset, previously used for the analysis of MOST relationships for structure parameters, is extended for the mean vertical gradients and standard deviations of potential temperature, specific humidity, and wind. Also, local-free-convection (LFC) similarity is studied. The LES data suggest that the MOST functions for mean gradients are universal and unique. The data for the mean gradient of the horizontal wind display significant scatter, while the gradients of temperature and humidity vary considerably less. The LES results suggest that this scatter is mostly related to a transition from MOST to LFC scaling when approaching free-convective conditions and that it is associated with a change of the slope of the similarity functions toward the expected value from LFC scaling. Overall, the data show slightly, but consistent, steeper slopes of the similarity functions than suggested in literature. The MOST functions for standard deviations appear to be unique and universal when the entrainment from the free atmosphere into the boundary layer is sufficiently small. If entrainment becomes significant, however, we find that the standard deviation of humidity no longer follows MOST. Under free-convective conditions, the similarity functions should reduce to universal constants (LFC scaling). This is supported by the LES data, showing only little scatter, but displaying a systematic height dependence of these constants. Like for MOST, the LFC similarity constant for the standard deviation of specific humidity becomes nonuniversal when the entrainment of dry air reaches significant levels.

scholarly journals Characterization of the Martian Convective Boundary Layer

2009 ◽  
Vol 66 (7) ◽  
pp. 2044-2058 ◽  
Author(s):  
Germán Martínez ◽  
Francisco Valero ◽  
Luis Vázquez
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Standard Deviation ◽  
Wind Speed ◽  
Viscous Dissipation ◽  
Mixed Layer ◽  
Dissipation Rate ◽  
Horizontal Wind

Abstract The authors have carried out an extensive characterization of the Martian mixed layer formed under convective conditions. The values of the mixed layer height, convective velocity scale, convective temperature scale, mean temperature standard deviation, mean horizontal and vertical velocity standard deviations, and mean turbulent viscous dissipation rate have been obtained during the strongest convective hours for the mixed layer. In addition, the existing database of the surface layer has been improved by recalculating some parameters (e.g., Monin–Obukhov length, friction velocity, or scale temperature) that had already been obtained in previous papers by other means and also by calculating new ones, such as the standard deviation of the vertical wind speed velocity, the turbulent viscous dissipation rate, and eddy transfer coefficients for momentum and heat. The Earth counterparts of all these magnitudes are also shown. In this paper, a comprehensive database concerning the whole convective planetary boundary layer on Mars is displayed, and a detailed terrestrial comparison is established. The inputs of this work are hourly in situ temperature, hourly in situ horizontal wind speed, and hourly simulated ground temperature for specific selected Sols of the Viking and Pathfinder landers. These data correspond to typical low and midlatitude northern summertime conditions, with weak prevailing winds. To handle this set of data, surface layer and mixed layer similarity theory have been used at the strongest convective hours. In addition, the inclusion of a parameterization of a molecular sublayer and prescribed values of the surface roughness has been considered.

scholarly journals Eulerian versus Lagrangian Approaches to the Wave-Induced Transport in the Upper Ocean

2006 ◽  
Vol 36 (11) ◽  
pp. 2106-2118 ◽  
Author(s):  
Jan Erik H. Weber ◽  
Göran Broström ◽  
Øyvind Saetra
Keyword(s):  
Surface Layer ◽  
Wave Spectrum ◽  
Fluid Motion ◽  
Vertical Direction ◽  
Navier Stokes ◽  
Horizontal Wind ◽  
Form Drag ◽  
Navier Stokes Equation ◽  
Strong Winds ◽  
Wave Induced

Abstract It is demonstrated that the Eulerian and the Lagrangian descriptions of fluid motion yield the same form for the mean wave-induced volume fluxes in the surface layer of a viscous rotating ocean. In the Eulerian case, the volume fluxes are obtained in the familiar way by integrating the horizontal components of the Navier–Stokes equation in the vertical direction, as seen, for example, in the book by Phillips. In the direct Lagrangian approach, the perturbation equations for the second-order mean drift are integrated in the vertical direction. This yields the advantage that the form drag, which is a source term for the wave-induced transports, can be related to the virtual wave stress that acts to transfer dissipated mean wave momentum into mean currents. In particular, for waves that are periodic in space and time, comparisons between empirical and theoretical relations for the form drag yield an estimate for the wave-induced bulk turbulent eddy viscosity in the surface layer. A simplistic approach extends this analysis to account for wave breaking. By a generalization from a wave component to a wave spectrum, a set of equations for the wave-induced transport in the surface layer is derived for a fully developed sea. Solutions are discussed for an idealized spectral formulation. The problem is formulated such that a numerical wave prediction model can be used to generate the wave-forcing terms in a numerical barotropic ocean surge model. Results from the numerical simulations with a wave-influenced surge model are discussed and compared with similar results from forcing the surge model only by the traditional mean horizontal wind stress computed from the 10-m wind speed. For the simulations presented here, the wave-induced stress constitutes about 50% of the total atmospheric stress for moderate to strong winds.

scholarly journals Turbulent characteristics of a semiarid atmospheric surface layer from cup anemometers – effects of soil tillage treatment (Northern Spain)

2003 ◽  
Vol 21 (10) ◽  
pp. 2119-2131 ◽  
Author(s):  
S. Yahaya ◽  
J. P. Frangi ◽  
D. C. Richard
Keyword(s):  
Surface Roughness ◽  
Surface Layer ◽  
Dissipation Rate ◽  
Atmospheric Surface Layer ◽  
Friction Velocity ◽  
Roughness Length ◽  
Energy Dissipation Rate ◽  
Horizontal Wind ◽  
Length Scale ◽  
Integral Scale

Abstract. This paper deals with the characteristics of turbulent flow over two agricultural plots with various tillage treatments in a fallow, semiarid area (Central Aragon, Spain). The main dynamic characteristics of the Atmospheric Surface Layer (ASL) measured over the experimental site (friction velocity, roughness length, etc.), and energy budget, have been presented previously (Frangi and Richard, 2000). The current study is based on experimental measurements performed with cup anemometers located in the vicinity of the ground at 5 different levels (from 0.25 to 4 m) and sampled at 1 Hz. It reveals that the horizontal wind variance, the Eulerian integral scales, the frequency range of turbulence and the turbulent kinetic energy dissipation rate are affected by the surface roughness. In the vicinity of the ground surface, the horizontal wind variance logarithmically increases with height, directly in relation to the friction velocity and the roughness length scale. It was found that the time integral scale (and subsequently the length integral scale) increased with the surface roughness and decreased with the anemometer height. These variations imply some shifts in the meteorological spectral gap and some variations of the spectral peak length scale. The turbulent energy dissipation rate, affected by the soil roughness, shows a z-less stratification behaviour under stable conditions. In addition to the characterization of the studied ASL, this paper intends to show which turbulence characteristics, and under what conditions, are accessible through the cup anemometer.Key words. Meteorology and atmospheric dynamics (climatology, turbulence, instruments and techniques)

The characteristics of turbulent velocity components in the surface layer under convective conditions

1977 ◽  
Vol 11 (3) ◽  
pp. 355-361 ◽  
Author(s):  
H. A. Panofsky ◽  
H. Tennekes ◽  
D. H. Lenschow ◽  
J. C. Wyngaard
Keyword(s):  
Surface Layer ◽  
Turbulent Velocity ◽  
Convective Conditions

scholarly journals Similarity Hypotheses for the Atmospheric Surface Layer Expressed by Non-Dimensional Characteristic Invariants – A Review

2009 ◽  
Vol 3 (1) ◽  
pp. 48-79 ◽  
Author(s):  
Gerhard Kramm ◽  
Fritz Herbert
Keyword(s):  
Surface Layer ◽  
Atmospheric Surface Layer ◽  
Friction Velocity ◽  
Vertical Component ◽  
Universal Constant ◽  
Eddy Flux ◽  
Convective Conditions ◽  
Mathematical Relationship ◽  
Similarity Functions ◽  
Flux Profile

In this paper, similarity hypotheses for the atmospheric surface layer (ASL) are reviewed using nondimensional characteristic invariants, referred to as π-numbers. The basic idea of this dimensional π-invariants analysis (sometimes also called Buckingham’s π-theorem) is described in a mathematically generalized formalism. To illustrate the task of this powerful method and how it can be applied to deduce a variety of reasonable solutions by the formalized procedure of non-dimensionalization, various instances are represented that are relevant to the turbulence transfer across the ASL and prevailing structure of ASL turbulence. Within the framework of our review we consider both (a) Monin- Obukhov scaling for forced-convective conditions, and (b) Prandtl-Obukhov-Priestley scaling for free-convective conditions. It is shown that in the various instances of Monin-Obukhov scaling generally two π-numbers occur that result in corresponding similarity functions. In contrast to that, Prandtl-Obukhov-Priestley scaling will lead to only one π number in each case usually considered as a non-dimensional universal constant. Since an explicit mathematical relationship for the similarity functions cannot be obtained from a dimensional π- invariants analysis, elementary laws of π-invariants have to be pointed out using empirical or/and theoretical findings. To evaluate empirical similarity functions usually considered within the framework flux-profile relationships, so-called integral similarity functions for momentum and sensible heat are presented and assessed on the basis of the friction velocity and the vertical component of the eddy flux densities of sensible and latent heat directly measured during the GREIV I 1974 field campaign.

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