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  • Author or Editor: Lawrence V. Lyjak x
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Lawrence V. Lyjak
and
Anne K. Smith

Abstract

Three-dimensional winds derived from LIMS satellite observations for the 1978/79 winter are used to compute the mean Lagrangian motion in the winter stratosphere. Material tubes of air parcels are initialized every 4 days and followed for periods of 10 days each. The initial positions of the tubes are chosen so that they lie along contours of constant geopotential and potential temperature. Maps of air parcel distributions give a qualitative picture of the degree of deformation of the material tubes with time. In addition, quantitative measures of the Lagrangian mean velocity and dispersion are computed.

During quiet periods, when the zonal wind is strong and the vortex is nearly axisymmetric, the air parcel tubes tend to remain coherent for the full 10 days of the integration. When the wave amplitudes are large, many of the tubes break and the parcels disperse. During the observed minor sudden warming, those tubes closest to the vortex center remained coherent with little distortion. In contrast, during the major sudden warming every material tube in the stratosphere was broken, and there was extensive mixing between air parcels from low and high latitudes.

Lagrangian mean vertical motion tended to be smaller than the motion in the transformed Eulerian coordinate system, which is sometimes used to represent the mean Lagrangian flow. The horizontal velocities determined from the Lagrangian parcel trajectories do not in general correspond well with the transformed Eulerian velocities. Largest differences in horizontal winds occur for situations during which the tubes underwent extensive deformation and the dispersion of air parcels was large. This suggests that the transformed Eulerian circulation is not capable of representing the horizontal Lagrangian motion when a large part of the latter is due to dispersive motion rather than to net displacements of coherent material tube.

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John C. Gille
and
Lawrence V. Lyjak

Abstract

One of the limitations to the accurate calculation of radiative heating and cooling rates in the stratosphere and mesosphere has been the lack of accurate data on the atmospheric temperature and composition. Data from the LIMS experiment on Nimbus-7 have been extended to the South Pole with the aid of other observations. The data have been used as input to codes developed by Ramanathan and Dickinson to calculate the individual components and the net radiative heating rates from 100–0.1 mb. Solar heating due to ozone, nitrogen dioxide, carbon dioxide, water vapor and oxygen is shown to be nearly balanced by cooling in the thermal infrared spectral region due to carbon dioxide, ozone and water vapor. In the lower stratosphere, infrared transfer by ozone leads to heating that is sensitive to the distribution of tropospheric ozone, clouds and water vapor.

The heating and cooling rates are adjusted slightly in order to satisfy the global mass balance. The results are in qualitative agreement with earlier calculations, but show additional detail. There is as strong temporal and vertical variation of cooling in the tropics. Radiative relaxation times are as short as 7 days or less at the stratopause.

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John C. Gille
,
Lawrence V. Lyjak
, and
Anne K. Smith

Abstract

The residual mean circulation (rmc) has been calculated from the transformed thermodynamic equation using LIMS (Limb Infrared Monitor of the Stratosphere) data for the 100–0.1 mb region. For discussion, it has been divided into two components: the diabatic circulation, associated with the diabatic heating, and the transient circulation, more directly connected to eddy activity. The slowly varying diabatic circulation reveals an equator-to-pole circulation at lower levels in the stratosphere, usually overlain by a summer-to-winter pole circulation. However, there are strong seasonal variations, so that the pole-to-pole circulation fills the entire region at the December solstice, while the equator-to-pole circulation extends to above 0.1 mb at the equinoxes. The transient circulation is characterized by rapid variations and small vertical and horizontal scales. Though generally smaller than the diabatic circulation, it can dominate in the lower stratosphere during disturbed conditions.

This circulation is consistent with the transformed momentum equation in the lower stratosphere (where drag is expected to be small) during undisturbed periods. It suggests a large drag due to small-scale waves (such as gravity waves) in the mesosphere, although the magnitudes are uncertain. The downward propagation of the semiannual oscillation causes the rmc in the tropics to vary, and it is capable of creating the equatorial water vapor maximum above 10 mb.

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Anne K. Smith
,
John C. Gille
, and
Lawrence V. Lyjak

Abstract

Using satellite data from the Nimbus 7 LIMS instrument, a previous study by Smith showed that interactions among planetary waves 1, 2 and 3 in the stratosphere were significant during January 1979. That month was characterized by an exceptionally large wave 1 amplitude in the stratosphere. The present study extends the analysis to the period November 1978–March 1979 to determine the conditions under which wave–wave interactions have a significant effect on variations in wave activity and on wave-mean flow interactions. A quantitative measure of how wave–wave interactions affect the wave activity of zonal waves 1 and 2 is obtained from the potential enstrophy budget.

The results demonstrate that the relative importance of wave–wave versus wave-mean flow interactions depends on the magnitude of the eddy mean wind and potential vorticity relative to the zonal means. When the zonal mean wind is weak, a relatively small amplitude wave tends to behave nonlinearly, whereas when the mean wind is strong, only large amplitude waves are significantly nonlinear. In the 1978–79 winter, the zonal mean wind was weaker and wave–wave interactions were more important in middle and late winter than during November–December.

Further evidence is presented that the vacillation between waves 1 and 2, which has been observed in the winter stratosphere of both hemispheres, is as strongly influenced by wave–wave interactions in the stratosphere as by variations in the forcing from the troposphere.

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