Estimating the Depth of the Daytime Convective Boundary Layer
01 Aug 1982-Journal of Applied Meteorology (American Meteorological Society)-Vol. 21, Iss: 8, pp 1123-1129
TL;DR: In this paper, three in-situ and five remote sensing techniques for measuring the height of the daytime convective boundary layer were compared, and good agreement between the different systems when the capping inversion was steep and well defined, and some variability when the stratification was not so sharply defined.
Abstract: Three in-situ and five remote sensing techniques for measuring the height of the daytime convective boundary layer were compared. There was, as a rule, good agreement between the different systems when the capping inversion was steep and well defined, and some variability when the stratification was not so sharply defined. Two indirect methods for estimating boundary-layer heights from the length scales of convective motions in the layer are also discussed.
Citations
More filters
TL;DR: In this paper, the authors present a review of the literature on the analysis of profile measurements and the use of parameterisations and simple models, and suggest for the preprocessor development and for future research activities.
898 citations
TL;DR: In this paper, the authors examine the methods and results of mixing height determination from sodar data that have been reported in the literature and discuss the theoretical base, the methods suggested, the automatization of algorithms, and the intercomparison of sodar-based mixing height values with data from independent measurements and models.
224 citations
TL;DR: In this paper, the authors examined the environmental conditions necessary for sustaining rolls and for influencing the aspect ratio, ratio of roll wavelength to convective boundary layer (CBL) depth, and orientation.
Abstract: Data from the Convection and Precipitation/Electrification (CaPE) project, as well as results from numerical simulations, are used to study horizontal convective rolls. The environmental conditions necessary for sustaining rolls and for influencing the aspect ratio, ratio of roll wavelength to convective boundary layer (CBL) depth, and orientation are examined. Observations and numerical model simulations both suggest that a moderate surface sensible heat flux and some vertical wind shear are necessary for roll existence. Unlike some previous studies, however, it is shown that rolls occurred within very low CBL shear conditions (∼2 × 10−3 s−1). In addition, the low-level (i.e., ∼200 m) shear seems to be more important than the shear through the depth of the CBL in roll sustenance. The aspect ratio is shown to be proportional to the CBL instability, measured in terms of the Monin–Obukhov length. The roll orientation is similar to the wind direction at 10 m AGL, the CBL wind direction, the inversio...
206 citations
Cites background from "Estimating the Depth of the Daytime..."
...Kuettner (1971) observed and theoretically predicted an aspect ratio (ratio of wavelength to CBL depth) of 2....
[...]
TL;DR: In this paper, a severe thunderstorm over North Dakota developed into a squall line and then into a mesoscale convective complex (MCC) with overshooting tops as high as ∼14 km and a cirrus anvil that covered more than 300,000 km2.
Abstract: On June 28, 1989, a severe thunderstorm over North Dakota developed into a squall line and then into a mesoscale convective complex (MCC) with overshooting tops as high as ∼14 km and a cirrus anvil that covered more than 300,000 km2. In this paper we describe the trace gas concentrations prior to, in, and around the storm; paper 2 presents numerical simulations. Observations of O3 and θeq unaffected by upstream convection for at least 3 days prior to the flights placed the undisturbed tropopause between 10.7 and 11 km. The anvil outflow, sampled at altitudes of 10.8 to 12.2 km, extended well into what used to be the stratosphere. Air inside the anvil was characterized by notably low concentrations of O3 and high CO relative to the out-of-cloud environment. Elevated concentrations of NO and NOy, due to lightning and upward transport, were observed in the anvil. A tongue of air with tropospheric characteristics lay above stratospheric air, showing that extensive stratosphere-troposphere exchange had occurred. The effects of this mechanism on atmospheric budgets of trace species depend on the fate of the air that enters the anvil and on the frequency of MCCs. Assuming that the symmetry was cylindrical and that the material transported during the observations at the east edge of the anvil was representative of the entire cirrus anvil cloud, we estimate a minimum flux of 2 × 1010 g of O3 into the troposphere and a maximum flux of 3–7 × 1013 g of H2O into the stratosphere. This is a greater flux of water than the stratospheric water budget can support, and thus most of this water must return to the troposphere; the ice crystals were of sufficient size to have substantial settling velocity. If, however, even a small fraction of the mass of such anvils remains in the stratosphere, then convective transport of reactive tropospheric trace species such as NOy, CO, and NMHC may dominate the chemistry of the lower stratosphere in this midlatitude region. More detailed estimates of the fluxes, taking into account the rear anvil as well, are presented in the companion paper.
168 citations
TL;DR: In this paper, a statistical analysis concerning the vertical distribution of the volume light extinction coefficients of particles derived from Raman lidar measurements at 10 EARLINET stations is presented, where the profiles were measured on a fixed schedule with up to two measurements per week; they typically covered the height range from 500 m to 6000 m above ground level (agl).
Abstract: [1] Since 2000, regular lidar observations of the vertical aerosol distribution over Europe have been performed within the framework of EARLINET, the European Aerosol Research Lidar Network. A statistical analysis concerning the vertical distribution of the volume light extinction coefficients of particles derived from Raman lidar measurements at 10 EARLINET stations is presented here. The profiles were measured on a fixed schedule with up to two measurements per week; they typically covered the height range from 500 m to 6000 m above ground level (agl). The analysis is made for the planetary boundary layer (PBL) as well as for several fixed layers above ground. The results show typical values of the aerosol extinction coefficient and the aerosol optical depth (AOD) in different parts of Europe, with highest values in southeastern Europe and lowest values in the northwestern part. Annual cycles and cumulative frequency distributions are also presented. We found that higher aerosol optical depths in southern Europe compared to the northern part are mainly attributed to larger amounts of aerosol in higher altitudes. At 9 of the 10 sites the frequency distribution of the aerosol optical depth in the planetary boundary layer follows a lognormal distribution at the 95% significance level.
167 citations
Cites methods from "Estimating the Depth of the Daytime..."
...It was validated against other methods to derive the PBL height [Coulter, 1979; Kaimal et al., 1982] showing good agreement under well mixed conditions....
[...]
References
More filters
TL;DR: In this article, numerical integrations are presented for a neutrally stratified planetary boundary layer containing a passive scalar, and for three unstable cases with upward heat flux, assuming the air is assumed unsaturated.
Abstract: Results of numerical integrations are presented for a neutrally stratified planetary boundary layer containing a passive scalar, and for three unstable cases with upward heat flux. The air is assumed unsaturated. A total of either 16,000 or 32,000 grid points was used in a three-dimensional region with length and width several times the height of the boundary layer. A key result is the irrelevance of the neutral height scale, u*/f, and its replacement by the height zi of the inversion base which confines the convective mixing when m and only for the two slightly unstable cases were the vertical velocity eddies distinctly elongated as in Ekman-layer theories. At large instabilities it is shown how the friction velocity u/* loses its influence upon the turbulence intensifies and a convective velocity wale becomes important. Vertical profiles of mean wind, potential tempe...
905 citations
TL;DR: In this paper, a boundary layer experiment conducted over a flat site in northwestern Minnesota is discussed, where wind and temperature fluctuations near the ground were measured with AFCRL's fast-response instrumentation on a 32 m tower with MRU probes attached at five different heights to the tethering cable of a 1300 m2 kite balloon.
Abstract: Results from a boundary layer experiment conducted over a flat site in northwestern Minnesota are discussed Wind and temperature fluctuations near the ground were measured with AFCRL's fast-response instrumentation on a 32 m tower Measurements between 32 m and the inversion base zi were made with MRU probes attached at five different heights to the tethering cable of a 1300 m2 kite balloon The daytime convective boundary layer appears to be well-mixed with evidence of significant heat and momentum entrainment through the capping inversion The spectra of velocity components are generalized within the framework of mixed-layer similarity The characteristic wavelength for w increases linearly with height up to z = 0l zi following free convection prediction, but approaches a limiting value of 15 zi, in the upper half of the boundary layer The characteristic wavelengths for u and v are maintained at approximately 15 zi down to heights very close to the ground This limiting wavelength correspo
889 citations
TL;DR: In this paper, a laboratory model of the unstable planetary boundary layer is presented and compared with atmospheric observations, showing that good agreement exists between the model measurements and the atmospheric observations when the variables are appropriately scaled with the depth of the mixed layer zi, and the convective velocity and temperature scales w* and T *.
Abstract: Experimental details of a laboratory model of the unstable planetary boundary layer are given. Measurements of vertical profiles of mean temperature and heat flux, and of velocity and temperature fluctuations are presented and compared with atmospheric observations. Good agreement exists between the model measurements and the atmospheric observations when the variables are appropriately scaled with the depth of the mixed layer zi, and the convective velocity and temperature scales w* and T*. Turbulence kinetic energy budgets for the mixed layer turbulence are presented. The buoyant energy production decreases nearly linearly with height, while the rate of dissipation of kinetic energy is found to be about constant with height. Horizontal temperature spectra at three heights are presented. The temperature spectrum for a height neat the middle of the mixed layer suggests the existence of an inertial subrange as well as a viscous-convective subrange. The temperature spectrum calculated from horizont...
392 citations
TL;DR: In this paper, it is suggested that the surplus turbulent kinetic energy is destroyed by buoyancy forces in a region of downward transfer of heat in the upper part of the convection layer.
Abstract: Viscous dissipation is inadequate to account for the destruction of all the thermal turbulence generated by upward transfer of heat in a deep convection layer. It is suggested that the surplus turbulent kinetic energy is destroyed by buoyancy forces in a region of downward transfer of heat in the upper part of the convection layer. This process is associated with mass transfer downwards through the convection (or subsidence) inversion and also with an upward movement of the inversion, though the latter may be overcome by sufficiently strong subsidence. A simple theory of the process is developed and the results deduced thereby agree well with observations of the diurnal variation of inversion height in Central Australia.
259 citations
TL;DR: In this paper, a steady-state neutral and unstable model for the atmospheric boundary layer is presented. But the model itself needs more attention now, particularly with respect to the higher-order terms in the pressure covariance expansions.
Abstract: Publisher Summary Higher order closure models, which use exact equations for the mean field and approximate ones for the turbulence, can reproduce in remarkable detail, the structure of turbulent shear flows. However, the main differences between models are the closure assumptions used for the turbulence equations. This chapter explains the model for the atmospheric boundary layer. Developing model for the atmospheric boundary layer is in some ways more difficult, because the effects of buoyancy and rotation modify the structural relationships found in shear flows and presumably, buoyant and rotation terms should appear in at least some of the closure assumptions. Another difficulty is the lack of atmospheric turbulence data outside the surface layer. However, the results presented in the chapter suggest that steady-state neutral and unstable model is an attractive approach to the calculation of atmospheric boundary layer structure and it takes relatively little computer time. There is a rational technique for refining the model, but, because the data required for model testing are so difficult to obtain in the atmosphere, it seems to have relied heavily on the simulation of various laboratory flows. However, the model itself needs more attention now, particularly with respect to the higher-order terms in the pressure covariance expansions.
114 citations