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- Author or Editor: James W. Deardorff x
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Abstract
A rather general formulation is utilized for the stability dependence of the eddy coefficient for heat KH above the lowest 50 m. It contains five empirical parameters which pertain to the magnitude of KH in neutral conditions, its variation with increasing stability, its variation with increasing instability, the extent of a slightly countergradient upward heat flux, and the height variation of KH in stable air above hilly terrain or above a cloud-capped inversion base. The five parameters were evaluated or checked against observations of the thermal modification of polar air moving from New England towards Bermuda, and of the diurnal temperature wave at O'Neill, Nebr. A detailed study of the effects of variation of any of the parameters upon the resultant potential temperature profile is included, as is also the effects of different rates of long-wave radiation, of different cloudiness, and of different large-scale subsidence than those assumed.
The empirically obtained formulation for KH giving best agreement has greater stability dependence than that found by previous investigators.
Abstract
A rather general formulation is utilized for the stability dependence of the eddy coefficient for heat KH above the lowest 50 m. It contains five empirical parameters which pertain to the magnitude of KH in neutral conditions, its variation with increasing stability, its variation with increasing instability, the extent of a slightly countergradient upward heat flux, and the height variation of KH in stable air above hilly terrain or above a cloud-capped inversion base. The five parameters were evaluated or checked against observations of the thermal modification of polar air moving from New England towards Bermuda, and of the diurnal temperature wave at O'Neill, Nebr. A detailed study of the effects of variation of any of the parameters upon the resultant potential temperature profile is included, as is also the effects of different rates of long-wave radiation, of different cloudiness, and of different large-scale subsidence than those assumed.
The empirically obtained formulation for KH giving best agreement has greater stability dependence than that found by previous investigators.
Abstract
The equation describing the production or decay of temperature fluctuations of the nth moment is derived and applied toward the determination of the sign of the small-scale heat flux and its vertical divergence in the atmosphere.
It is found that an upward heat flux is possible within a sub-adiabatic layer surmounting a super-adiabatic layer if the potential temperature does not increase with height by more than about 0.2C within the layer.
The vertical divergence of the heat flux in an unstable surface layer is found to be positive close to the ground, thereby compensating somewhat for strong radiational heating. It is found to be negative higher above the surface where the potential temperature decreases much more slowly with height provided the temperature variance diminishes with height. The divergence appears to be positive (negative) at the lower (upper) surface of an inversion and could therefore be a mechanism of maintenance of such a surface against the destructive effect of radiation.
Abstract
The equation describing the production or decay of temperature fluctuations of the nth moment is derived and applied toward the determination of the sign of the small-scale heat flux and its vertical divergence in the atmosphere.
It is found that an upward heat flux is possible within a sub-adiabatic layer surmounting a super-adiabatic layer if the potential temperature does not increase with height by more than about 0.2C within the layer.
The vertical divergence of the heat flux in an unstable surface layer is found to be positive close to the ground, thereby compensating somewhat for strong radiational heating. It is found to be negative higher above the surface where the potential temperature decreases much more slowly with height provided the temperature variance diminishes with height. The divergence appears to be positive (negative) at the lower (upper) surface of an inversion and could therefore be a mechanism of maintenance of such a surface against the destructive effect of radiation.
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Abstract
The surface stress and fluxes of heat and moisture are parameterized for use in numerical models of the general circulation of the atmosphere. The parameterization is designed to be consistent with recent advances in knowledge of both the planetary boundary layer and the surface layer. A key quantity throughout is the height, h, of the planetary boundary layer, which appears in the governing stability parameter, a bulk Richardson number. With upward heat flux, a time-dependent prediction equation is proposed for h that incorporates penetrative convection and vertical motion. Under stable conditions, h is assumed to depart from the neutral value and to become nearly proportional to the Monin-Obukhov length.
The roughness length, Zo , is incorporated in the combination h/zo , and the parameterization is consistent with h/zo affecting only the wind component in the direction of the surface velocity. The direction of the surface wind and stress is derived in a manner consistent with the known value of the surface pressure gradient and theoretical studies of the decrease of stress with height.
The parameterization has been tested numerically and appears to be efficient enough to use in existing general circulation models.
Abstract
The surface stress and fluxes of heat and moisture are parameterized for use in numerical models of the general circulation of the atmosphere. The parameterization is designed to be consistent with recent advances in knowledge of both the planetary boundary layer and the surface layer. A key quantity throughout is the height, h, of the planetary boundary layer, which appears in the governing stability parameter, a bulk Richardson number. With upward heat flux, a time-dependent prediction equation is proposed for h that incorporates penetrative convection and vertical motion. Under stable conditions, h is assumed to depart from the neutral value and to become nearly proportional to the Monin-Obukhov length.
The roughness length, Zo , is incorporated in the combination h/zo , and the parameterization is consistent with h/zo affecting only the wind component in the direction of the surface velocity. The direction of the surface wind and stress is derived in a manner consistent with the known value of the surface pressure gradient and theoretical studies of the decrease of stress with height.
The parameterization has been tested numerically and appears to be efficient enough to use in existing general circulation models.
