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C. B. Leovy

Abstract

A number of possible interaction mechanisms between internal gravity waves and radiative and photochemical processes at altitudes from 80 to 120 km are considered. The heat of recombination of atomic oxygen and absorption of solar radiation by ozone are both found to contribute to wave amplification. Growth rates are slow under normal conditions but can become significant if the atomic oxygen concentration below 100 km is increased above its normal values. This could be brought about by large-scale descending motion or by increased mixing near the mesopause.

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C. B. Leovy and T. Ackerman

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W. M. Wehrbein and C. B. Leovy

Abstract

An infrared radiative heating and cooling algorithm designed to be used with dynamical models of the middle atmosphere is described. A Curtis matrix is used to compute cooling by the 15 and 10 μm bands of carbon dioxide. Escape of radiation to space and exchange with the lower boundary are used for the 9.6 μm band of ozone. Voigt line shape, vibrational relaxation, line overlap, and the temperature dependence of line strength distributions and transmission functions are incorporated into the CO2 Curtis matrices. Radiative damping rates derived from this algorithm give a damping rate of ∼0.5 day−1 for temperature disturbances in the mesosphere of vertical extent 25 km. When this algorithm is employed in the dynamical model of Hotton and Wehrbein (1980) to calculate the zonal mean circulation of the middle atmosphere, the zonal and meridional circulations generated are nearly twice as strong as those generated in the model of Holten and Wehrbein (1980) which used a Newtonian cooling algorithm based on the radiation-to-space approximation of Dickinson (1973). Since the zonal circulation calculated with the new radiative algorithm is also much stronger than that observed, this result supports the assertion that there is a very efficient, but as yet obscure, mechanical damping mechanism in the mesosphere.

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T. P. Ackerman, K. N. Liou, and C. B. Leovy

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C. E. Leovy, R. W. Zurek, and J. B. Pollack

Abstract

Characteristics of the Mars global dust storm are reviewed. At the Mariner 9 encounter, the dust consisted of highly absorbing particles distributed rather uniformly up to great height (∼50 km). These observations together with temperature distributions inferred from the Mariner 9 IRIS by Hanel and his collaborators are used to estimate global wind systems during the dust storm. The global distribution and direction of light surface streaks indicate that the axially symmetric circulation was a dominant part of flow during the dust storm. An energy balance argument is used to estimate the intensity of the equatorial part of such a wind system. Surface winds driven by the diurnal and semidiurnal components of solar heating are also estimated. The axially symmetric winds may become strong enough to raise dust over wide areas of Mars' tropics under unusual conditions: the incoming solar radiation must be near its seasonal maximum, the static stability must be low, and the atmosphere must be able to absorb and re-emit a sizeable fraction of the incoming radiation. Emission is aided by the formation of H20 ice clouds in the winter northern polar region. Absorption is enhanced by the presence of a small dust opacity in the atmosphere prior to the onset of the global dust storm. Strong winds around the periphery of the retreating south polar cap would be driven by the temperature gradient at the cap edge and by the mass outflow due to subliming C02. These polar winds could generate local dust storms, raising the general level of dustiness, and providing the conditions necessary for onset of a global dust storm. Observational evidence for this sequence of events is discussed. The proposed model is sensitive to the precise phase relationship between Mars' perihelion and southern summer solstice, and variations in this phasing may have caused a strongly episodic behavior of dust storms and of a number of related planetary processes.

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Matthew H. Hitchman, Conway B. Leovy, John C. Gille, and Paul L. Bailey

Abstract

Data from the Limb Infrared Monitor of the Stratosphere (LIMS) are used to identify a new type of planetary scale disturbance in the equatorial lower mesosphere during northern winter 1978/79. The disturbances consist of two or three vertically stacked temperature extrema of alternating sign. They persist for as long as two weeks and do not propagate. Their occurrence is confined to regions of very weak or negative inertial stability, and their meridional to vertical aspect ratio, meridional structure and zonal spectrum are consistent with disturbances predicted by inertial instability theory. However, they are found only when there is strong forcing of the subtropical mesosphere by zonal wavenumber one and two Rossby waves. This fact, together with the absence of zonal propagation, suggests that stationary Rossby waves determine their occurrence and longitudinal structure. These structures can significantly modify the zonal mean flow and should be taken into account in dynamical models of the equatorial mesosphere.

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C.B. Leovy, C-R. Sun, M.H. Hitchman, E.E. Remsberg, J.M. Russell, III, L.L. Gordley, J.C. Gille, and L.V. Lyjak

Abstract

Data from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) for the period 25 October 1978–28 May 1979 are used in a descriptive study of ozone variations in the middle stratosphere. It is shown that the ozone distribution is strongly influenced by irreversible deformation associated with large amplitude planetary-scale waves. This process, which has been described by McIntyre and Palmer as planetary wave breaking, takes place throughout the 3–30 mb layer, and poleward transport of ozone within this layer occurs in narrow tongues drawn out of the tropics and subtropics in association with major and minor warming events. Thew events complement the zonal mean diabatic circulation in producing significant changes in the total column amount of ozone.

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