The Convective Boundary Layer

The Monin-Obukhov length L is not a parameter that is routinely measured. Recognizing the need for a readily usable way to define atmospheric stability based on routine observations, Pasquill (1961) introduced the concept of stability classes defined in Table 16.3. These classes have proved very useful in atmospheric diffusion calculations, as we will see shortly. 

When turbulence in the atmospheric boundary layer is maintained largely by buoyant production, the boundary layer is said to be in a convective state. The source of buoyancy is the upward heat flux originating from the ground heated by solar radiation. Convective turbulence is relatively vigorous and causes rapid vertical mixing in the atmospheric boundary layer. 

The height of the atmospheric or planetary boundary layer under neutral conditions can be estimated from (Blackadar and Tennekes, 1968) 

The determination of Zp under unstable conditions is usually not critical to performing atmospheric diffusion calculations because a temperature inversion layer, which limits the extent of vertical mixing, is generally present at some height Zi well below Zp. 

From the definition of the Monin-Obukhov length, shear production of turbulence is confined to a layer of height on the order of L. Under convective conditions, then, we expect 

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Venkatram (1980) has summarized the aspects of dispersion in the convective boundary layer ... 

Lamb, R. G., and Duran, D. R. (1977). Eddy diffusivities derived from a numerical model of the convective boundary layer. Nuov. Cimento [1] 1C, 1-17. 

Venkatram, A. (1980). The relationship between the convective boundary layer and dispersion from tall stacks. Atmos. Environ. 14, 763-767. 

Schumann, U. 1989. Large eddy simulation of turbulent diffusion with chemical reactions in the convective boundary layer. Atmospheric Environment 23(8) 1713-26. 

Moeng, C.H., and Wyngaard, J.C. (1988) Spectral analysis of large-eddy simulations of the convective boundary layer, J. Atmos. Sci. 45, 3573-3587. 

Petersen AC, Beets C, van Hop H, Duynkerke PG, Siebesma AP (1999) Mass-Flux Characteristics of Reactive Scalars in the Convective Boundary Layer. J... 

In the convective-boundary layer region W(1) of the diffusion wake, molecular diffusion can be neglected. The concentration here depends only on the... 

Raupach, M. R. (2000). Equilibrium evaporation and the convective boundary layer. Boundary-Layer Meteorol. 96,107-141. 

Sawford, B. L. and Guest, F. M. (1987). Lagrangian stochastic analysis of flux-gradient relationships in the convective boundary layer. /. Atmos. Sri. 44,1152-1165. 

The value of E in relation to like the value of gj, indicates the evaporative nature of the surface so E < E q or E/Ee, < 1 reflects surface dryness or stomatal closure as well as the balance of energy exchange between the atmosphere and the underlying surface. By definition, E > Ef, can be caused only by advection. As implied above with respect to the partitioning of temperature, this may also result from the entrainment of dry air from above the convective boundary layer that develops daily over the earth surface. To further illustrate the relation between E and Ef, in terms of surface characteristics, it is helpful to write the Penman-Monteith equation (Monteith and Unsworth, 1990),... 

Petersen AC, Beets C, van Hop H, Duynkerke PG, Siebesma AP (1999) Mass-flux characteristics of reactive scalars in the convective boundary layer. J Atmos Science 56 37-56 Pope S (2000) Turbulent flows. Cambridge University Press, Cambridge Prandtl L (1904) Uber Hlissigkeitsbewegungen bei sehr kleiner Reibung. Verhandlg III Intern Math Kongr Heidelberg, pp 484-491 NULL... 

Schumann U (1989) Laige-eddy simulation of the turbulent diffusion with chemical reactions in the convective boundary layer. Atmos Environ 23(8) 1713-1727 Schumann U (1992) Simulations and parameterizations of laige eddies in convective atmospheric boundary layers. In Proceedings of a workshop held at the European Centre for Medium-Range Weather Forecasts (ECMWF) on Fine Scale Modelling and the Development of Parameterization Schemes, 16-18 September 1991, ECMWF Shames IH (1962) Mechemics of fluids. McGraw-Hill, New York... 

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