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| Titel |
Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere |
| VerfasserIn |
V. Barabash, A. Osepian, P. Dalin |
| 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. 3 ; Nr. 32, no. 3 (2014-03-11), S.207-222 |
| Datensatznummer |
250121034
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| Publikation (Nr.) |
 copernicus.org/angeo-32-207-2014.pdf |
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| Zusammenfassung |
| Mesospheric water vapour concentration effects on the ion composition and
electron density in the lower ionosphere under quiet geophysical conditions
were examined. Water vapour is an important compound in the mesosphere and
the lower thermosphere that affects ion composition due to hydrogen radical
production and consequently modifies the electron number density. Recent
lower-ionosphere investigations have primarily concentrated on the
geomagnetic disturbance periods. Meanwhile, studies on the electron density
under quiet conditions are quite rare. The goal of this study is to
contribute to a better understanding of the ionospheric parameter responses
to water vapour variability in the quiet lower ionosphere. By applying a
numerical D region ion chemistry model, we evaluated efficiencies for the
channels forming hydrated cluster ions from the NO+ and O2+
primary ions (i.e. NO+.H2O and O2+.H2O,
respectively), and the channel forming H+(H2O)n proton
hydrates from water clusters at different altitudes using profiles with low
and high water vapour concentrations. Profiles for positive ions, effective
recombination coefficients and electrons were modelled for three particular
cases using electron density measurements obtained during rocket campaigns.
It was found that the water vapour concentration variations in the mesosphere
affect the position of both the Cl2+ proton hydrate layer upper
border, comprising the NO+(H2O)n and
O2+(H2O)n hydrated cluster ions, and the
Cl1+ hydrate cluster layer lower border, comprising the
H+(H2O)n pure proton hydrates, as well as the numerical
cluster densities. The water variations caused large changes in the effective
recombination coefficient and electron density between altitudes of 75 and
87 km. However, the effective recombination coefficient, αeff, and electron number density did not respond even to large
water vapour concentration variations occurring at other altitudes in the
mesosphere. We determined the water vapour concentration upper limit at
altitudes between 75 and 87 km, beyond which the water vapour concentration
ceases to influence the numerical densities of Cl2+ and Cl1+,
the effective recombination coefficient and the electron number density
in the summer ionosphere. This water vapour concentration limit corresponds
to values found in the H2O-1 profile that was observed in the summer
mesosphere by the Upper Atmosphere Research Satellite (UARS). The electron density modelled using the
H2O-1 profile agreed well with the electron density measured in the
summer ionosphere when the measured profiles did not have sharp gradients.
For sharp gradients in electron and positive ion number densities, a water
profile that can reproduce the characteristic behaviour of the ionospheric
parameters should have an inhomogeneous height distribution of water vapour. |
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