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  • GEOPHYSICS  (17)
  • 1985-1989  (17)
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  • 1
    Publication Date: 2011-08-19
    Description: Laboratory kinetic studies suggest that an appreciable fraction of the ozone produced by recombination of atomic oxygen is vibrationally excited in the nu3 mode. Further, laboratory data are available for the physical quenching of nu3, its radiative relaxation, and its radiative excitation by resonant absorption. It is shown that these chemical and physical processes are likely to result in substantial departures from local thermodynamic equilibrium for the nu3 mode of ozone in the mesosphere and therefore have important effects on infrared mesospheric ozone measurments by emission in the 9.6-micron band. Implications of these effects on data from the Limb Infrared Monitor of the Stratosphere (Remsberg et al, 1984), particularly their night/day ratio, are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 9865-987
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  • 2
    Publication Date: 2011-08-19
    Description: Observations of NO2 from the limb infrared monitor of the stratosphere (LIMS) experiment in high-latitude summer are presented. Appropriate selection of latitude and days during the month of May yields NO2 observations obtained during the afternoon and evening at solar zenith angles ranging from about 35-110 deg. These data show that the NO2 abundances in the stratosphere become strongly dependent on the solar zenith angle for angles exceeding about 80 deg. Model calculations and other observations suggest that from about 80-95 deg this dependence probably reflects variations in the propagation of the visible radiation that photodissociates NO2. The data obtained at zenith angles greater than about 95 deg provide clear evidence for the night decay of NO2 to form N2O5, and the observed decay rate is shown to be consistent with present theory.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 5455-546
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  • 3
    Publication Date: 2011-08-19
    Description: The detailed photochemistry of methane oxidation has been studied in a coupled chemical/dynamical model of the middle atmosphere. The photochemistry of formaldehyde plays an important role in determining the production of water vapor from methane oxidation. At high latitudes, the production and transport of molecular hydrogen is particularly important in determining the water vapor distribution. It is shown that the ratio of the methane vertical gradient to the water vapor vertical gradient at any particular latitude should not be expected to be precisely 2, due both to photochemical and dynamical effects. Modeled H2O profiles are compared with measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment at various latitudes. Molecular hydrogen is shown to be responsible for the formation of a secondary maximum displayed by the model water vapor profiles in high latitude summer, a feature also found in the LIMS data.
    Keywords: GEOPHYSICS
    Type: Royal Meteorological Society, Quarterly Journal (ISSN 0035-9009); 114; 281-295
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  • 4
    Publication Date: 2011-08-19
    Description: The solar proton event of July 13, 1982 produced considerable ionization in the polar-cap mesosphere. Energetic solar proton fluxes were measured by the NOAA-6 satellite. The DE-2 satellite measured the low-energy electrons, the ion drift velocity, and other atmospheric and ionospheric properties during the event in the region of the measured maximum electric field (189 mV/m at 2215 UT near 60 deg N), a Joule heating rate of 1-3 K/day is calculated between 70 and 80 km, exceeding the heating due to ozone absorption at noon in the summer hemisphere in that altitude range. The Joule heating rate above 90 km greatly exceeded 20 K/day. The calculated height-integrated Joule heating rate above 100 km in the same region exceeded 400 ergs/sq cm sec, and DE-2 near 350 km measured neutral winds of nearly 1000 m/s and neutral gas temperatures of over 2000 K. The overall ionospheric structure calculated below the DE-2 satellite is described.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 6083-609
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  • 5
    Publication Date: 2011-08-19
    Description: Current understanding of stratospheric transport in the meridional plane is reviewed, and the implications of that conceptual framework for the ozone response to chlorofluorocarbon increases are considered. The possibility of seasonal and latitudinal variations in that response is stressed. Calculations of the changes in ozone that may have occurred between the period before widespread chlorofluorocarbon usage and the present day, and the changes that would be expected to occur at steady state for 1980 chlorofluorocarbon production levels, are presented. Finally, some of the uncertainties in the adopted transport framework and its applicability to the evaluation of future perturbations are explored.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 12
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  • 6
    Publication Date: 2011-08-19
    Description: Seasonal variations of the OH-asterisk (7-5) mesospheric hydroxyl emission at 1.89 microns observed by the SME near-IR spectrometer are compared with the theoretical predictions of a two-dimensional dynamical/chemical model. The good agreement found at low latitudes for both dayglow and nightglow provides support for the model assumption that breaking gravity waves induce seasonal and latitudinal variations in diffusion. The seasonal behavior of atomic hydrogen in the upper mesosphere (related to vertical transport) and/or uncertainties in the OH Meinel band parameters are proposed as possible explanations for the discrepancy noted between model and observational data for the middle latitudes.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0980-8752); 7; 365-374
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  • 7
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: Observations of O2 1Delta(g) emission during solar proton events reveal large depletions below 80 and near 90 km. The lower-altitude depletions are believed to be due to odd hydrogen production and associated depletion of ozone, but the mechanism producing the depletion near 90 km has not yet been established. In this paper, it is proposed that an exothermic charge exchange reaction between O2(+) and O2 1Delta(g) is likely to be responsible for these high-altitude depletions. In particular, it is shown that the vertical structure of the observed change in airglow emission is consistent with this mechanism.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 35; 1087-109
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  • 8
    Publication Date: 2011-08-19
    Description: The influence of seasonal and latitudinal changes in the distribution of mesospheric components on the OH Meinel-band nightglow is investigated by means of numerical simulations using the two-dimensional dynamical/chemical model of Garcia and Solomon (1985). The processes responsible for the formation and destruction of vibrationally excited OH in the mesosphere are described; the seasonal/latitudinal evolution for the higher (v greater than 6) and lower (v = 1-6) levels is shown in graphs and maps and characterized in detail; and the theoretical results are compared with published observational data. The lower-level emission is shown to depend on both O and H, suggesting that the variation of the Meinel-band nightglow can provide important information on the roles of advection and diffusion in the transport of water vapor and odd oxygen near the mesopause.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 35; 977-989
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  • 9
    Publication Date: 2011-08-19
    Description: Eddy diffusion and momentum forcing in the mesosphere and lower thermosphere arise principally from the effects of breaking gravity and waves. The propagation and dissipation of gravity waves depend strongly on season and latitude because of its relationship to the background zonal wind. These processes have significant effects on the transport of chemical species in that region, so that observations of variations in chemical constituents provide useful tracers for dynamical theory. A parameterization of gravity wave propagation and dissipation was incorporated in the coupled dynamical-chemical model to study these effects. Several easily observable airglow features of the mesosphere-thermosphere region are shown to provide sensitive indications of gravity wave influence. In particular, theoretical predictions of large seasonal and latitudinal variations in the atomic oxygen green line, the Meinal bands of excited OH, and the O3 densities inferred from O2 (delta supra 1 sub g) emission at altitudes from 75 to 90 km are shown to be in remarkably good agreement with observations. Implications of these sensitive chemical tracers for the dynamics of the mesosphere-lower thermosphere region and its relationship to gravity waves are discussed.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions Handbook for MAP, Vol. 18; 1 p
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  • 10
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: The zonally averaged radiative balance of the stratosphere based on the measured temperature structure and gas concentrations available from the LIMS instrument is examined in detail. These data are extant for seven months (November 1978 to May 1979). The contribution to the net radiative balance due to the individual components of solar heating and longwave cooling is discussed. These components are further broken down by individual gas constituent to understand the role each gas plays in determining the total radiative heating/cooling. The deficiencies of employing a latitudinally and temporally independent Newtonian damping coefficient are also explored. In particular, the Newtonian damping time is shown to vary by a factor of two in both latitude and season. Net zonally averaged stratospheric radiative heating for the seven months of LIMS data are presented. These net heating rates are important in determining the role of advective transport of chemical constituents. An important feature that appears in the derived radiative heating is the existence of a region of net radiative cooling near the equatorial stratopause.
    Keywords: GEOPHYSICS
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 43; 1525-153
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