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- Author or Editor: Peter J. Gierasch x
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Abstract
A meridional cell, with rising motion near the equator and sinking near the poles, transports angular momentum upward in an atmosphere whenever equatorial regions of the atmosphere have an angular momentum surplus relative to polar regions. This process way contribute to the maintenance of the Venus atmospheric super-rotation.
Super-rotation by this process is exhibited in a simple analytical model. The super-rotation ratio in the model is derived to be exp (HD 2/vvm ), where H is depth in scale heights, D the mean scale height, vv the vertical eddy diffusivity, and tm the meridional overturning time.
For the mechanism to work, some eddy process must maintain an angular momentum surplus in equatorial regions. Vorticity mixing is suggested. It is also demonstrated that if the Richardson number is large in a cyclostrophic atmosphere, the mean thermal structure is given by global radiative equilibrium, and local deviations from equilibrium are balanced by adiabatic cooling or warming associated with vertical motions.
Abstract
A meridional cell, with rising motion near the equator and sinking near the poles, transports angular momentum upward in an atmosphere whenever equatorial regions of the atmosphere have an angular momentum surplus relative to polar regions. This process way contribute to the maintenance of the Venus atmospheric super-rotation.
Super-rotation by this process is exhibited in a simple analytical model. The super-rotation ratio in the model is derived to be exp (HD 2/vvm ), where H is depth in scale heights, D the mean scale height, vv the vertical eddy diffusivity, and tm the meridional overturning time.
For the mechanism to work, some eddy process must maintain an angular momentum surplus in equatorial regions. Vorticity mixing is suggested. It is also demonstrated that if the Richardson number is large in a cyclostrophic atmosphere, the mean thermal structure is given by global radiative equilibrium, and local deviations from equilibrium are balanced by adiabatic cooling or warming associated with vertical motions.
Abstract
The form of the diurnal thermal wave driven by a harmonically oscillating ground temperature into a semi-infinite homogeneous non-grey absorbing atmosphere is studied, neglecting convection and molecular conduction. Results are calculated for the terrestrial atmosphere and, with fair accuracy, for the martian atmosphere. The penetration heights are about 10 m and 200 m, respectively. In both cases the wave amplitude decays at large heights inversely with the height, and the phase lag relative to the ground approaches ϕ/2.
The grey-absorption solution and the solution predicted by the quasi-transparent model of Gierasch and Goody are compared with the non-grey one. The grey solution is qualitatively good if the absorption coefficient is chosen so that the penetration depth equals that of the non-grey solution.
The effects of convective heat transport are discussed.
Abstract
The form of the diurnal thermal wave driven by a harmonically oscillating ground temperature into a semi-infinite homogeneous non-grey absorbing atmosphere is studied, neglecting convection and molecular conduction. Results are calculated for the terrestrial atmosphere and, with fair accuracy, for the martian atmosphere. The penetration heights are about 10 m and 200 m, respectively. In both cases the wave amplitude decays at large heights inversely with the height, and the phase lag relative to the ground approaches ϕ/2.
The grey-absorption solution and the solution predicted by the quasi-transparent model of Gierasch and Goody are compared with the non-grey one. The grey solution is qualitatively good if the absorption coefficient is chosen so that the penetration depth equals that of the non-grey solution.
The effects of convective heat transport are discussed.
Abstract
The energy relationships for an atmosphere are reviewed and it is pointed out that the role of viscous dissipation can be examined from either a mechanical or a thermodynamic point of view. An entropy integral is derived which represents a constraint on the thermal structure of an atmosphere in the case of zero viscous dissipation. The size of dissipation in actual atmospheres is not very well known. Calculations of thermal structure are performed for the Martian atmosphere, with the results depending greatly on whether high or low dissipation is assumed; better information, therefore, is highly desirable. In the case of low dissipation, the Martian tropopause is high and cold; so cold that C02 clouds form.
Abstract
The energy relationships for an atmosphere are reviewed and it is pointed out that the role of viscous dissipation can be examined from either a mechanical or a thermodynamic point of view. An entropy integral is derived which represents a constraint on the thermal structure of an atmosphere in the case of zero viscous dissipation. The size of dissipation in actual atmospheres is not very well known. Calculations of thermal structure are performed for the Martian atmosphere, with the results depending greatly on whether high or low dissipation is assumed; better information, therefore, is highly desirable. In the case of low dissipation, the Martian tropopause is high and cold; so cold that C02 clouds form.
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If Mars has permanent CO2 polar caps, atmospheric heat transport may cause the atmospheric pressure to be extremely sensitive to variations of solar heating at the poles. This could happen because atmospheric heating depends on density, which depends strongly on the polar temperature through the vapor pressure relation. A simple climatological model is used to study the question.
Abstract
If Mars has permanent CO2 polar caps, atmospheric heat transport may cause the atmospheric pressure to be extremely sensitive to variations of solar heating at the poles. This could happen because atmospheric heating depends on density, which depends strongly on the polar temperature through the vapor pressure relation. A simple climatological model is used to study the question.
Abstract
We examine a propagating wave interpretation of the temperature profile features observed in the Jovian upper atmosphere by Veverka et al. Inertia-gravity waves with frequencies on the order of 3 × 10−3 sec−1 are consistent with the data. If the interpretation is correct, and if the waves carry energy upward, it implies 1) that there is excitation of such waves at lower levels, 2) that eddy diffusivities on the order of 106 cm2 sec−1 are probably generated by the waves, and 3) that the energy carried by waves is important to the upper atmospheric heat balance.
Abstract
We examine a propagating wave interpretation of the temperature profile features observed in the Jovian upper atmosphere by Veverka et al. Inertia-gravity waves with frequencies on the order of 3 × 10−3 sec−1 are consistent with the data. If the interpretation is correct, and if the waves carry energy upward, it implies 1) that there is excitation of such waves at lower levels, 2) that eddy diffusivities on the order of 106 cm2 sec−1 are probably generated by the waves, and 3) that the energy carried by waves is important to the upper atmospheric heat balance.
Abstract
We have computed radiative decay times for thermal disturbances near the cloud tops of Jupiter and conclude that they are much larger than probable dynamical time constants. Under these circumstances radiative equilibrium calculations are of little significance.
Abstract
We have computed radiative decay times for thermal disturbances near the cloud tops of Jupiter and conclude that they are much larger than probable dynamical time constants. Under these circumstances radiative equilibrium calculations are of little significance.
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Abstract
The compositions of the atmospheres of the outer planets are dominated by molecular hydrogen. The hydrogen ortho and para forms (proton spins parallel and antiparallel) are observed to have ratios that are not in thermodynamic equilibrium, with spatial variations, probably due to vertical motions that transport fluid from a different temperature regime. Conversion between the two forms produces significant “latent heat” release, but conversion is thought to be so slow that this heating is extremely small. Because the two forms of hydrogen have different specific heats and their abundance ratio is spatially variable, Ertel's potential vorticity is not conserved, even in the adiabatic and frictionless limit. In this paper the degree of nonconservation is assessed by scale analysis, for typical observed ortho–para inhomogeneity. A numerical example similar to Jupiter's Great Red Spot is presented. Analysis is restricted to large-scale motions in the stable upper tropospheres of the planets, where the quasigeostrophic approximation applies. A major result is that a generalization of quasigeostrophic potential vorticity is still conserved, and that the para fraction is merely an inert tracer in this regime. The Ertel isentropic potential vorticity is not conserved, even to leading order, except in special regions where the ortho– para ratio is exceptionally homogeneous.
Abstract
The compositions of the atmospheres of the outer planets are dominated by molecular hydrogen. The hydrogen ortho and para forms (proton spins parallel and antiparallel) are observed to have ratios that are not in thermodynamic equilibrium, with spatial variations, probably due to vertical motions that transport fluid from a different temperature regime. Conversion between the two forms produces significant “latent heat” release, but conversion is thought to be so slow that this heating is extremely small. Because the two forms of hydrogen have different specific heats and their abundance ratio is spatially variable, Ertel's potential vorticity is not conserved, even in the adiabatic and frictionless limit. In this paper the degree of nonconservation is assessed by scale analysis, for typical observed ortho–para inhomogeneity. A numerical example similar to Jupiter's Great Red Spot is presented. Analysis is restricted to large-scale motions in the stable upper tropospheres of the planets, where the quasigeostrophic approximation applies. A major result is that a generalization of quasigeostrophic potential vorticity is still conserved, and that the para fraction is merely an inert tracer in this regime. The Ertel isentropic potential vorticity is not conserved, even to leading order, except in special regions where the ortho– para ratio is exceptionally homogeneous.
