Parameterized processes in the surface boundary layer of an atmospheric circulation model

Abstract

A general circulation model is modified successively by adding five new features in the lower boundary layer; namely, (i) a different roughness parameter over land and sea, (ii) a Monin-Obukhov type treatment of the turbulent transfer process in the constant-flux layer, (iii) a Richardson number dependent parameterization for E h a n layer process, (iv) a diurnal variation of insolation, and (v) heat conduction into the soil. To assess the effect of each, the experiments are repeated by gradually increasing the complexity of the model. The circulation model has relatively low horizontal grid resolution and 9 vertical levels, and it is applied to a winter case for 14 day predictions. The results indicate that the sophistication of the boundary layer physics does not produce a particularly large effect on the synoptic scale prediction until about 7 days. Its effect may become large after 10 days. One noteworthy result is that the effect of the diurnal variation of insolation is not great for the free atmosphere but an influence is effectively transferred in the vertical, if the Richardson number dependent parameterization for the Ekman layer process is incorporated. The entire study is a preliminary test, the purpose of which is to determine the relative magnitude of each effect. A detailed comparison with observed data was not attempted.

A parametric model of vertical eddy fluxes in the atmosphere

“…This is not possible analytically in unstable conditions, but it can be done numerically, by iterations. Such a method has been used in some boundary-layer models (e.g., Delsol et al (1971); Busch et al (1976)). However, for maximum speed of computation, we want to avoid iterative methods.…”

The derivation of a numerical diagnostic model for the forcing of the geopotential

“…The frictional stress at the Earth's surface is given by v τ = ρC d |V sfc |V sfc (Lettau, 1959;Pedlosky, 1987, sections 2.8 and 3.12) with the drag coefficient C d = 2 × 10 −3 proposed by Delsol et al(1971) and Holloway and Manabe (1971). Thus, term 12 becomes…”

Theoretical studies of the parameterization of the non-neutral surface boundary layer

“…The quantitative analysis of these models was carried out in the entire stability range -2 ~< z/L ~< 2 on the basis of the high quality SM-formulas of Clarke (1970) and Delsol et al (1971). The computed z/L-distributions of scaling height S~, viscous dissipation S~ as well as turbulent and thermal energy transport SE and Sw are represented in Figures 1 to 4 as dashed, dotted and dashed-dotted curves for the three models, respectively.…”