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- Author or Editor: Richard S. Lindzen x
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Abstract
The author reexamines the Charney–Drazin problem with special attention to the concentration of potential vorticity gradient in the neighborhood of the tropopause. It is found that the degree of concentration has a profound effect on the response to stationary forcing, with greater concentration leading to greater response. Smoothing the concentration either analytically or numerically (by using coarser resolution) both lead to reduced responses, especially at higher wavenumbers. The results suggest a potentially important interaction between baroclinically unstable eddies and stationary waves. Insofar as the former act to mix potential vorticity in the troposphere while concentrating gradients at tropopause levels, they significantly condition the basic state for the latter.
Abstract
The author reexamines the Charney–Drazin problem with special attention to the concentration of potential vorticity gradient in the neighborhood of the tropopause. It is found that the degree of concentration has a profound effect on the response to stationary forcing, with greater concentration leading to greater response. Smoothing the concentration either analytically or numerically (by using coarser resolution) both lead to reduced responses, especially at higher wavenumbers. The results suggest a potentially important interaction between baroclinically unstable eddies and stationary waves. Insofar as the former act to mix potential vorticity in the troposphere while concentrating gradients at tropopause levels, they significantly condition the basic state for the latter.
Abstract
The response of the mesosphere to slow fluctuations in ultraviolet and visible radiation intensity is investigated using the simplified models for photochemistry and radiative transfer developed by Lindzen and Goody (1965). Fluctuations in oxygen's ultraviolet bands, ozone's ultraviolet bands and ozone's visible band are separately considered. It is found that the mesosphere is most sensitive to fluctuations in ozone's ultraviolet bands above 35 km and to fluctuations in oxygen's ultraviolet bands above 30 km. At levels of peak sensitivity, fluctuations of about 12 per cent in either of these bands will give rise to temperature fluctuations of 2 deg K. This appears to rule out minute changes in solar ultraviolet emission as a cause for the ‘26-month’ oscillation in the equatorial mesosphere. It is also found that the mesosphere is quite sensitive to fluctuations in visible light in the region between 20 and 35 km where fluctuations of 3–6 per cent in visible radiation can give rise to fluctuations of 2 deg K in temperature. On the average, about 26 per cent of the visible radiation in the mesosphere is received via reflection from below. Much of the reflection is from clouds and hence, variation in cloud cover forms an effective way of varying visible light in the mesosphere. In this connection it is found that the winter distribution of cloud cover in the subarctic is such as to introduce into the mesosphere a temperature disturbance whose amplitude and spatial distribution are such as to be able to trigger a sudden warming of the Northern Hemisphere winter variety.
Abstract
The response of the mesosphere to slow fluctuations in ultraviolet and visible radiation intensity is investigated using the simplified models for photochemistry and radiative transfer developed by Lindzen and Goody (1965). Fluctuations in oxygen's ultraviolet bands, ozone's ultraviolet bands and ozone's visible band are separately considered. It is found that the mesosphere is most sensitive to fluctuations in ozone's ultraviolet bands above 35 km and to fluctuations in oxygen's ultraviolet bands above 30 km. At levels of peak sensitivity, fluctuations of about 12 per cent in either of these bands will give rise to temperature fluctuations of 2 deg K. This appears to rule out minute changes in solar ultraviolet emission as a cause for the ‘26-month’ oscillation in the equatorial mesosphere. It is also found that the mesosphere is quite sensitive to fluctuations in visible light in the region between 20 and 35 km where fluctuations of 3–6 per cent in visible radiation can give rise to fluctuations of 2 deg K in temperature. On the average, about 26 per cent of the visible radiation in the mesosphere is received via reflection from below. Much of the reflection is from clouds and hence, variation in cloud cover forms an effective way of varying visible light in the mesosphere. In this connection it is found that the winter distribution of cloud cover in the subarctic is such as to introduce into the mesosphere a temperature disturbance whose amplitude and spatial distribution are such as to be able to trigger a sudden warming of the Northern Hemisphere winter variety.
Abstract
An equivalent depth of 10 m for the oscillations of the tropical atmosphere was suggested by wave-CISK calculations. It is here shown that the dispersive properties of such an atmosphere are in agreement with observed power spectra for southerly and westerly winds.
Abstract
An equivalent depth of 10 m for the oscillations of the tropical atmosphere was suggested by wave-CISK calculations. It is here shown that the dispersive properties of such an atmosphere are in agreement with observed power spectra for southerly and westerly winds.
Abstract
This paper considers the vertical propagation of a long-period, small-amplitude perturbation in a medium in which radiative transfer and photochemistry play important roles. The perturbation and the basic field are assumed to be axially symmetric and symmetric about the equator; the basic wind field is geostrophic and the basic temperature field is in radiative equilibrium.
It is found that long-period perturbations can only propagate by virtue of the physical effects of radiative transfer and photochemistry. The computed wave propagates downwards and, for a period of 2.2 years, the phase speed is close to the observed speed of 1.5 km month−1 for the “26-month” equatorial oscillation. The observed relative phases of velocity and temperature fields, and the sharp attenuation of the oscillation below 20 to 25 km are also found in the model wave.
There are discrepancies between the model and the observed “26-month” oscillation, which are to be expected in view of the nonlinearity of the observed phenomenon. However, it appears that, for complex reasons, the observed wave may satisfy equations similar to those occurring in the linear theory.
Abstract
This paper considers the vertical propagation of a long-period, small-amplitude perturbation in a medium in which radiative transfer and photochemistry play important roles. The perturbation and the basic field are assumed to be axially symmetric and symmetric about the equator; the basic wind field is geostrophic and the basic temperature field is in radiative equilibrium.
It is found that long-period perturbations can only propagate by virtue of the physical effects of radiative transfer and photochemistry. The computed wave propagates downwards and, for a period of 2.2 years, the phase speed is close to the observed speed of 1.5 km month−1 for the “26-month” equatorial oscillation. The observed relative phases of velocity and temperature fields, and the sharp attenuation of the oscillation below 20 to 25 km are also found in the model wave.
There are discrepancies between the model and the observed “26-month” oscillation, which are to be expected in view of the nonlinearity of the observed phenomenon. However, it appears that, for complex reasons, the observed wave may satisfy equations similar to those occurring in the linear theory.
Abstract
The general problem of the vertical propagation of equatorial waves through mean fields with vertical shear is solved analytically for all meridional wavenumbers using asymptotic multiple-scale methods. The results are used to show that the mixed gravity-Rossby wave is not the only easterly wave capable of penetrating the stratosphere, while the Kelvin wave is the only westerly wave capable of doing so. The results are also used to evaluate the effects of mean wind on diurnal tides.
Abstract
The general problem of the vertical propagation of equatorial waves through mean fields with vertical shear is solved analytically for all meridional wavenumbers using asymptotic multiple-scale methods. The results are used to show that the mixed gravity-Rossby wave is not the only easterly wave capable of penetrating the stratosphere, while the Kelvin wave is the only westerly wave capable of doing so. The results are also used to evaluate the effects of mean wind on diurnal tides.
Abstract
The stability of a baroclinic, axially symmetric vortex on an f-plane to axially symmetric disturbances is investigated. It is found that with photochemistry and radiative transfer acting, such disturbances are unstable regardless of the value of the Richardson number. The growth rates under conditions relevant to the mesosphere are, however, very small.
Abstract
The stability of a baroclinic, axially symmetric vortex on an f-plane to axially symmetric disturbances is investigated. It is found that with photochemistry and radiative transfer acting, such disturbances are unstable regardless of the value of the Richardson number. The growth rates under conditions relevant to the mesosphere are, however, very small.
Abstract
The parameters of conventional atmospheric tidal theory which vary from planet to planet are isolated and evaluated for Earth, Mars and Venus. The assumptions of tidal theory are investigated in order to determine their validity for Mars and Venus.
Abstract
The parameters of conventional atmospheric tidal theory which vary from planet to planet are isolated and evaluated for Earth, Mars and Venus. The assumptions of tidal theory are investigated in order to determine their validity for Mars and Venus.
Abstract
Laplace's tidal equation for diurnal tides of longitudinal number one is investigated. It is found that in addition to the previously found solutions (Hough Functions) corresponding to positive equivalent, depths there are also Hough Functions corresponding to negative equivalent, depths. Both are necessary for the representation of observed tidal data.
As an application of the Hough Functions the diurnal surface pressure oscillation resulting from diurnal variations in insolation is computed. It is found that the insolation model due to Siebert can account for only one-third of the observed pressure oscillation.
Abstract
Laplace's tidal equation for diurnal tides of longitudinal number one is investigated. It is found that in addition to the previously found solutions (Hough Functions) corresponding to positive equivalent, depths there are also Hough Functions corresponding to negative equivalent, depths. Both are necessary for the representation of observed tidal data.
As an application of the Hough Functions the diurnal surface pressure oscillation resulting from diurnal variations in insolation is computed. It is found that the insolation model due to Siebert can account for only one-third of the observed pressure oscillation.
Abstract
It is suggested that an additional source of semidiurnal forcing due to daily variations in tropical rainfall could correct the discrepancy between the calculated phase (boned on forcing due to insulation absorption by ozone and water vapor) and that observed for the surface pressure oscillation. It is also shown that the 180° phase shift in horizontal wind oscillations at 28 km which current calculations predict, but which is not observed, would he eliminated by the proposed additional forcing. The magnitude and phase of the required rainfall oscillation is calculated and found to be consistent with existing observations. Finally, it is shown that the convergence field due to the tide could not directly account for the rainfall oscillation.
Abstract
It is suggested that an additional source of semidiurnal forcing due to daily variations in tropical rainfall could correct the discrepancy between the calculated phase (boned on forcing due to insulation absorption by ozone and water vapor) and that observed for the surface pressure oscillation. It is also shown that the 180° phase shift in horizontal wind oscillations at 28 km which current calculations predict, but which is not observed, would he eliminated by the proposed additional forcing. The magnitude and phase of the required rainfall oscillation is calculated and found to be consistent with existing observations. Finally, it is shown that the convergence field due to the tide could not directly account for the rainfall oscillation.
Abstract
No Abstract available.
Abstract
No Abstract available.
