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  • 1
    Publication Date: 2011-08-24
    Description: Observations of the nearly inert, man-made chlorofluorocarbon CFC-115 obtained during January 1989 are used to infer the age of air in the lower stratosphere. These observations together with estimated release rates suggest an average age of high-latitude air at pressure altitudes near 17-21 km of about 3 to 5 yr. This information is used together with direct measurements of HCFC-22, HCFC-142b, CH3Br, H-1301, H-1211, and H-2402 to examine the fractional dissociation of these species within the Arctic polar lower stratosphere compared to that of CFC-11 and hence to estimate their local ozone depletion potentials in this region. It is shown that these HCFCs are much less efficiently dissociated within the stratosphere than CFC-11, lowering their ozone depletion potentials to only about 30-40 percent of their chlorine loading potentials. In contrast, the observations of CH3Br and the Halons considered confirm that they are rapidly dissociated within the stratosphere, with important implications for their ozone depletion potentials.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; D12,; 12
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  • 2
    Publication Date: 2011-08-19
    Description: The pairwise correlation of NO(y) and N2O data from the Southern and Northern Hemispheres is presented. Both data sets show a linear correlation region, defined as a reference state, and regions of denitrification where the correlation breaks down. Using two-dimensional photochemical model simulations of the atmosphere, a similar linear correlation is found between NO(y) and N2O, thereby establishing a theoretical framework for the reference state. This general approach, which can be extended to other pairs of molecules, should prove to be powerful in further comparisons of aircraft data with numerical models.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 345; 698-702
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Publication Date: 2011-08-19
    Description: During the 1988/89 Airborne Arctic Stratospheric Expedition (AASE), observations of the chemical composition, aerosol characteristics and atmospheric state were obtained from two aircraft, a NASA ER-2 and a DC-8. This paper presents a diagnosis of observations obtained using the ER-2 on January 24, 1989, using a Lagrangian coupled microphysical-photochemical model. The high chlorine monoxide mixing ratios observed from the ER-2 on the afternoon of January 24, 1989 are interpreted as a result of in situ heterogeneous release of reactive chlorine from the reservoirs HCl and CIONO2 on type-1 polar stratospheric cloud particles observed to be present at that time. This essential element in theories of polar ozone depletion has never before been observed directly in the stratosphere.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 541-544
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  • 7
    Publication Date: 2011-08-19
    Description: During the 1988/89 Airborne Arctic Stratospheric Expedition (AASE) observations of the chemical composition and aerosol characteristics of the winter vortex were obtained from a NASA ER-2 aircraft. In this paper we present interpretations of observations obtained on three ER-2 flights using a Lagrangian coupled photochemical-microphysical model. It is argued that observations obtained on Jaunary 16 and 19, and February 10, represent different stages of the chemical evolution of the vortex, from the early stages of chlorine release, the onset of denitrification and the intensively processed state.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 549-552
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  • 8
    Publication Date: 2011-08-19
    Description: Rapid adiabatic cooling induced by synoptic forcing led to polar stratospheric cloud (PSC) formation on January 24, 1989, at altitudes sampled by the ER-2 aircraft. Particle characteristics measured by the Forward Scattering Spectrometer Probe (FSSP) on the ER-2 were compared to those calculated using a theoretical PSC microphysics model. Although calculations were sensitive to local changes in cooling rate, generally favorable agreement was found, that in particle surface area being especially important since this parameter dictates heterogeneous chemical rates. The overall model performance suggests that the current approach for simulating Type 1 (nitric acid trihydrate) PSC formation under rapid cooling conditions is well founded and can be used to study the effects of heterogeneous chemistry on stratospheric composition.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 537-540
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  • 9
    Publication Date: 2011-08-19
    Description: The northern winter polar vortex is more disturbed dynamically and warmer than the Antarctic equivalent, and correspondingly fewer polar stratospheric clouds (PSCs) are observed to form. However, the rapid flow of stratospheric air through slow moving synoptically forced PSC regions can result in exposure of both vortical and extra vortical air to PSCs intermittently throughout the winter months. This periodic exposure to PSCs may be sufficient to perturb the chemical composition of large volumes of nothern hemisphere air. The synoptic forcing also leads to marked meridional flow which has a profound effect on chemical composition, having major impacts on both short term ozone depletion and the longer term recovery to lower ClOx abundances. Accurate simulation of the air flow is thus essential for the reliable calculation of ozone loss in polar regions.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 545-548
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  • 10
    Publication Date: 2011-08-24
    Description: A linear reference relationship between O3 and N2O has been used to estimate polar winter O3 loss from aircraft data taken in the lower stratosphere. Here, this relationship is evaluated at high latitudes by comparing it with a 2D model simulation and with NIMBUS 7 satellite measurements. Although comparisons with satellite measurements are limited to January through May, the model simulations are compared during other seasons. The model simulations and the satellite data are found to be consistent with the winter O3 loss analysis. It is shown that such analyses are likely to be inappropriate during other seasons.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; 939-944
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