Review and intercomparison of operational methods for the determination of the mixing height

A simple prognostic model of the depth of the stable boundary layer is developed which includes both the possibilities of growth due to entrainment and decreasing depth associated with turbulence decay. The model is designed to avoid requirement of surface fluxes and instead uses information on profiles of mean wind and temperature. Resulting coefficients for the model are estimated by comparisons with existing studies in the literature and comparison with Wangara data.

Modelling the depth of the stable boundary-layer

The evolutionary cycle of the nocturnal radiation inversion layer, from formation through the time of erosion under fair weather summer conditions was investigated by time-series analyses of observations of inversion base and top heights, and inversion strength at an urban and a nonurban site in St. Louis, Missouri. The time-dependent behavior of each inversion parameter is presented from statistical and least-squares regression analyses. Differences of inversion evolution between these sites are discussed. A surface-based inversion generally formed before sunset at the nonurban site, and the growth of the inversion top height has been described quite well by (2KTt)½, where KT is the thermal eddy coefficient. The average time of formation of an elevated inversion layer at the urban site was 2.5 h after sunset. The height of the nocturnal urban boundary layer decreased after formation under steady wind conditions. The urban mixing height was consistently higher during the morning than at the nonur...

Evolution of the Nocturnal Inversion Layer at an Urban and Nonurban Location

Particle model simulation of diffusion in low wind speed stable conditions

The performance of diagnostic equations for the stable boundary layer height h is evaluated with four observational datasets that represent a broad range of latitudes, land use, and surface roughness. In addition, large-eddy simulation results are used. Special care is given to data-quality selection. The diagnostic equations evaluated are so-called multilimit equations as derived by Zilitinkevich and coworkers in a number of papers. It appears that these equations show a serious negative bias, especially for h < 100 m, and it was found that the parameters involved could not be determined uniquely with calibration. As an alternative, dimensional analysis is used here to derive a formulation for h that is more robust. The formulation depends on the surface friction velocity u*, surface buoyancy flux Bs, Coriolis parameter, and the free-flow stability N. The relevance of the Coriolis parameter for the boundary layer height estimation in practice is also discussed. If the Coriolis parameter is ignor...

Diagnostic Equations for the Stable Boundary Layer Height: Evaluation and Dimensional Analysis

A theoretical model for vertical distribution of air temperature in lower layers during night-time calm periods has been developed by modifying some boundary conditions of the classical Brunt's model, on the ground of a more realistic behaviour of low atmosphere.

The model allows the vertical temperature profile to be deduced from screen data records and it fits with experimental data collected from a meteorological tower better than the classical model.

Radiative heat exchange is assumed to play the principal role, with diffusion thermal coefficient constant with height and time; previous work has shown that such an assumption holds true in the Po Valley air flow, when sky is cloudless and winds are light.

Forecasting of vertical temperature profiles in the atmosphere during nocturnal radiation inversions from air temperature trend at screen height

An application of lidar technique to the study of the nocturnal radiation inversion

Lidar measurement of plume rise and dispersion at Ostiglia power station.

Lateral and vertical crosswind standard deviations of Lagrangian tracers at small scale (100–1000 m) have been evaluated during five experimental periods of 15 days at two different Italian sites-a flat country (Po Valley) and a coastal region (La Spezia Gulf)-by a moving-average method applied to single trajectories of no-lift balloons tracked by two theodolites. Values of σy and σz as a function of downwind distance in the 102–103 m range were grouped following the Pasquill stability scheme (Pasquill, 1974) and regression lines for each category (from A to E) were drawn and compared (for the two sites) with earlier estimates, i.e., Pasquill-Gifford, Singer-Smith and Moore. On the one hand, the results show a general agreement with the above estimates and, on the other, the effects of mixing-height changes during the day and the effects of different climatological conditions.

A. Longhetto

Papers

Forecasting of vertical temperature profiles in the atmosphere during nocturnal radiation inversions from air temperature trend at screen height

An application of lidar technique to the study of the nocturnal radiation inversion

Lidar measurement of plume rise and dispersion at Ostiglia power station.

Experimental Evaluation of Diffusion Parameters on a Local Scale by Means of No-Lift Balloons

Some improvements in the balanced pilot balloons technique