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  • 1
    Electronic Resource
    Electronic Resource
    Precambrian glaciations and the evolution of the atmosphere (1994)
    Springer
    Annales geophysicae 12 (1994), S. 674-682 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Precambrian glaciations appear to be confined to two periods, one in the early Proterozoic between 2.5 and 2 Gyears BP (Before Present) and the other in the late Proterozoic between 1 and 0.57 Gyear BP. Possible reasons for these broad features of the Precambrian climate have been investigated using a simple model for the mean surface temperature of the Earth that partially compensates for the evolution of the Sun by variations in the atmospheric CO2 content caused by outgassing, the formation of continents and the weathering of the Earth’s land surface. It is shown that the model can explain the main changes in the Precambrian climate if the early Proterozoic glaciations were caused by a major episode of continental land building commencing about 3 Gyears BP while the late Proterozoic glaciations resulted from biologicallyenhanced weathering of the land surface due to the proliferation of life forms in the transition from the Proterozoic to the Phanerozoic that began about 1 Gyear BP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0674-3
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Partially coherent scattering models for the formation of the chromospheric Ca ii K line (1974)
    Springer
    Solar physics 38 (1974), S. 367-376 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss a model for the formation of the chromospheric Ca ii K line which does not make the usual assumption of complete redistribution. Using a physically reasonable scattering model, we find significant departures due to the frequency dependence of the line source function, particularly in the relative intensity and centre-to-limb behaviour of the K1 parts of the line and in the asymmetry produced by differential velocity fields. We conclude that the frequency dependence of the K line source function must be considered in quantitative models for the formation of the K line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155074
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The role of water-vapour photodissociation on the formation of a deep minimum in mesopause ozone (1998)
    Springer
    Annales geophysicae 16 (1998), S. 189-196 
    Details
    ISSN: 0992-7689
    Keywords: Atmospheric composition and structure ; Middle atmosphere ; Thermosphere ; Transmission and scattering of radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A one-dimensional atmospheric photochemical model with an altitude grid of about 1.5 km was used to examine the structure of the global mean vertical ozone profile and its night-time-to-daytime variation in the upper atmosphere. Two distinct ozone layers are predicted, separated by a sharp drop in the ozone concentration near the mesopause. This naturally occurring mesopause ozone deep minimum is primarily produced by the rapid increase in the destruction of water vapour, and hence increase in HOx, at altitudes between 80 and 85 km, a region where water-vapour photodissociation by ultraviolet radiation of the solar Lyman-alpha line is significant, and where the supply of water vapour is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. The model indicates that the depth of the mesopause ozone minimum is limited by the efficiency with which inactive molecular hydrogen is produced, either by the conversion of atomic hydrogen to molecular hydrogen via one of the reaction channels of H with HO2, or by Lyman-alpha photodissociation of water vapour via the channel that leads to the production of molecular hydrogen. The ozone concentration rapidly recovers above 85 km due to the rapid increase in O produced by the photodissociation of O2 by absorption of ultraviolet solar radiation in the Schumann-Runge bands and continuum. Above 90 km, there is a decrease in ozone due to photolysis as the production of ozone through the three-body recombination of O2 and O becomes slower with decreasing pressure. The model also predicts two peaks in the night-time/daytime ozone ratio, one near 75 km and the other near 110 km, plus a strong peak in the night-time/daytime ratio of OH near 110 km. Recent observational evidence supports the predictions of the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0189-4
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Atmospheric carbon dioxide and the long-term control of the Earth’s climate (1995)
    Springer
    Annales geophysicae 13 (1995), S. 782-790 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A CO2-weathering model has been used to explore the possible evolution of the Earth’s climate as the Sun steadily brightened throughout geologic time. The results of the model calculations can be described in terms of three, qualitatively different, “Megaclimates”. Mega-climate 1 resulted from a period of rapid outgassing in the early Archean, with high, but declining, temperatures caused by the small weathering rates on a largely water-covered planet. Mega-climate 2 began about 3 Gyear ago as major continental land masses developed, increasing the weathering rate in the early Proterozoic and thereby depleting the atmospheric CO2 concentration. This process produced the first Precambrian glaciations about 2.3 Gyear ago. During Mega-climate 2, evolutionary biological processes increased the surface weatherability in incremental steps and plate tectonics modulated the CO2 outgassing rate with an estimated period of 150 Myear (approximately one-half the period for the formation and breakup of super continents). Throughout Mega-climate 2 the surface temperature was controlled by variations in the atmospheric CO2 level allowing transitions between glacial and non-glacial conditions. The results of the model for Mega-climate 2 are in agreement with the occurrence (and absence) of glaciations in the geologic record. Extending the model to the future suggests that CO2 control of the Earth’s temperature will no longer be able to compensate for a solar flux that continues to increase. The present level of atmospheric CO2 is so small that further reduction in CO2 cannot prevent the Earth from experiencing Mega-climate 3 with steadily increasing surface temperatures caused by the continued brightening of the Sun. During Mega-climate 3, the main danger to the biosphere would come not from an increasing temperature but from a decreasing (rather than an increasing) CO2 level which could, in time, fall below 0.5 PAL, causing serious damage to the biosphere. Fortunately, the rates of change due to solar brightening are slow enough that Mega-climate 3 appears to pose no threat to the biosphere for the next 0.5-2 Gyear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0782-8
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Resonance line scattering from optically thin structures located above the solar limb (1978)
    Springer
    Solar physics 57 (1978), S. 27-36 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the formation of emission lines by resonance scattering from optically thin structures located above the solar limb. When the scattered radiation is only partially redistributed in frequency and angle, the resulting coherency is sufficient to affect the interpretation of such lines. In particular the apparent Doppler width of the scattered line may be different from the Doppler width in the scattering structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152041
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    Paper (German National Licenses)
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