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| Titel |
Specific features of eddy turbulence in the turbopause region |
| VerfasserIn |
M. N. Vlasov, M. C. Kelley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 32, no. 4 ; Nr. 32, no. 4 (2014-04-15), S.431-442 |
| Datensatznummer |
250121051
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| Publikation (Nr.) |
 copernicus.org/angeo-32-431-2014.pdf |
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| Zusammenfassung |
| The turbopause region is characterized by transition from the mean molecular
mass (constant with altitude) to the mean mass (dependent on altitude). The
former is provided by eddy turbulence, and the latter is induced by molecular
diffusion. Competition between these processes provides the transition from
the homosphere to the heterosphere. The turbopause altitude can be defined by
equalizing the eddy and molecular diffusion coefficients and can be located
in the upper mesosphere or the lower thermosphere. The height distributions
of chemical inert gases very clearly demonstrate the transition from
turbulent mixing to the diffusive separation of these gases. Using the height
distributions of the chemical inert constituents He, Ar, and N2 given by
the MSIS-E-90 model and the continuity equations, the height distribution of
the eddy diffusion coefficient in the turbopause region can be inferred. The
eddy diffusion coefficient always strongly reduces in the turbopause region.
According to our results, eddy turbulence above its peak always cools the
atmosphere. However, the cooling rates calculated with the eddy heat
transport coefficient equaled to the eddy diffusion coefficient were found to
be much larger than the cooling rates corresponding to the neutral
temperatures given by the MSIS-E-90 model. The same results were obtained for
the eddy diffusion coefficients inferred from different experimental data.
The main cause of this large cooling is the very steep negative gradient of
the eddy heat transport coefficient, which is equal to the eddy diffusion
coefficient if uniform turbulence takes place in the turbopause region.
Analysis of wind shear shows that localized turbulence can develop in the
turbopause region. In this case, eddy heat transport is not so effective and
the strong discrepancy between cooling induced by eddy turbulence and cooling
corresponding to the temperature given by the MSIS-E-90 model can be removed. |
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