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Neal Butchart and Ellis E. Remsberg

Abstract

Data retrieved from the LIMS (Limb lnfrared Monitor of the Stratosphere) experiment are used 10 calculate daily isentropic distributions of Ertel's potential vorticity, ozone, water vapor and nitric acid at the 850 K level in the Northern Hemisphere stratosphere for the period 25 October 1978 through 2 April 1979. Systematic redistributions of the quasi-conservative tracers are investigated by following the evolutions of the horizontal projection of the areas enclosed by isopleths of tracer on the isentropic surface. If the horizontal velocity is nondivergent on an isentropic surface, the areas change in response to nonconservative processes and /or irreversible mixing to unresolvable scales and so provide a diagnostic for quantifying the net cited of these two processes. The effects of the seasonal variation of the solar heating on the areas are identified from the evolutions of the hemispheric means and, for the potential vorticity, from a comparison with an annual Mile integration of a zonally symmetric, general circulation model. Superimposed on the seasonal trends are changes in areas on shorter time scales, and the LIMS potential vorticity, ozone and water vapor distributions each show the distinctive “surf-zone, main–,vortex structure” described by McIntyre and Palmer. As winter progresses the main vortex decreases in size while the surf zone expands. The evidence of the observations, combined with estimates of the strength of the radiative processes acting on the potential vorticity field, indicates fairly convincingly that irreversible mixing is an important mechanism involved in the formation of the surf-zone, main-vortex structure, and the subsequent erosion in size of the vortex. In addition, there is evidence of strong diabatic cross-isentropic transport of air parcels in the surf zone acting to restore the large-scale gradients destroyed by the mixing. The only LIMS measured constituent for which mixing was not always the dominant mechanism of redistribution was nitric acid, and it is speculated that the effects of dynamically induced changes to the effective sources and sinks of nitric acid on the 850 K surface are overshadowing other processes, at least in late January and February. Implications to tracer transport studies are examined by using the isentropic potential vorticity field as a basis for calculating low resolution approximations to the Lagrangian-mean tracer mixing ratios. The results demonstrate the feasibility of the approach to the longer-species but indicate a need for further research to distinguish between dynamical and radiactive/photochemical effects.

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Ellis E. Remsberg and Gerard E. Woodbury

Abstract

The role of atmospheric stability in the lowest 30 m in characterizing the dispersion of the primary pollutants CO, NO and hydrocarbons is investigated using the 1976 air quality data set for St. Louis. Stability is determined in three separate ways—from tower measurements of the vertical temperature gradient DT, tower measurements of wind speed u, and an approximation to the bulk Richardson number B̄ based only on DT and u in the surface layer.

High positive correlation coefficients were obtained between area averages of DT and each of the species for the inner urban area of St. Louis. Because the species concentrations were derived from a non-uniform area source, similar correlations at individual stations were somewhat poorer. At night, for low wind speed, the area-averaged species correlation coefficients for DT and are positive and significant, but they are poor for wind speed alone. For all other situations, correlation diagrams for wind speed versus species show appreciable scatter, and B̄, as it has been used in this study, is not a sensitive parameter for estimating surface pollutant concentrations. Use of a stability parameter that includes the mixed layer height, in addition to DT and u, will result in a quantity that exhibits a greater range for correlation studies. These findings should be considered when urban air quality models are parameterized and evaluated in terms of their ability to disperse primary pollutant distributions.

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T. Miles, W. L. Grose, E. E. Remsberg, and G. Lingenfelser

Abstract

The evolution of zonal wind and zonal wavenumber one (wave 1) in the Southern Hemisphere subpolar middle atmosphere is described for the period December 1978–May 1979 using temperature and ozone measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment.

In late December maximum zonal easterlies of ∼ −70 m s−1 are observed at 0.1 mb, 60°S. A zonal flow reversal occurs during late February and westerlies subsequently increase to 60–70 m s−1 in the upper stratosphere by April–May. LIMS zonal winds are compared with rocketsonde measurements and nadir sounder (derived) winds for summer and autumn. Although quantitative agreement is found at stratospheric levels, substantial discrepancies are evident in the mesosphere, most likely a reflection of sampling and resolution differences in the respective datasets.

Stationary and traveling wave 1 temperature disturbances (amplitudes ∼1–2 K at 60°S) are observed by LIMS during summer. The stationary wave is confined to the lower stratosphere near the level of zero zonal mean wind flow, whereas the traveling wave is prominent in the middle stratosphere, moves west at a rate similar to the zonal-mean wind, and exhibits a vertical-meridional structure similar to a P1 4 normal mode Rossby wave. A substantial intensification of wave 1 activity occurs during autumn (amplitudes ∼5–10 K), which is found to be associated with an upward-directed Eliassen–Palm flux near the subpolar tropopause level. Evidence relating wave 1 activity in the lower-middle stratosphere to the occurrence of zonal ozone perturbations of 10%–20% amplitude is presented for summer and autumn.

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Ellis E. Remsberg, Kenneth V. Haggard, and James M. Russell III

Abstract

The most widely used version of the Nimbus-7 LIMS middle atmosphere dataset is the set of high quality, daily, and zonal Fourier coefficients that resolve information out to six wavenumbers at 12 UTC. A Kalman filter algorithm was applied to the original profile data in order to generate those fields for the data archive or LAMAT product. The characteristics and implementation of the algorithm are described in some detail, along with examples of the output for each of the LIMS parameters. Criteria for judging the quality of the derived results are discussed and include: (i) standard deviation of the fit between individual profiles and the mapped field at the same longitudes, (ii) comparisons between the separate analyses of the ascending and descending orbital mode coefficients, (iii) continuity of the fields with latitude and pressure and (iv) comparisons of sequences of daily maps of the different parameters. The degree to which the filter fits the original data is determined by the estimated precision of the satellite measurements.

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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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