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| Titel |
Mid-mesospheric radar echoes: recent observations with a novel MST-radar and implications for the scattering mechanism |
| VerfasserIn |
M. Rapp, R. Latteck, P. Hoffmann, M. Zecha, G. Stober, T. Renkwitz, W. Singer |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066434
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| Zusammenfassung |
| The novel Middle Atmosphere ALOMAR Radar System (MAARSY) has been used to study
radar echoes from mid mesospheric altitudes, i.e., from ~60 – 80 km. Compared to
previously used radar systems, MAARSY possesses a much enhanced sensitivity for the
detection of these echoes due to its large transmitted power of ~800 kW and an antenna
aperture of approximately 6300 m2. Owing to this large sensitivity, echoes have been
observed throughout the entire year but show a pronounced maximum of occurrence during
winter months. The echoes further reveal a clear diurnal variation which is mainly driven by
the diurnal variation of Ly-α ionization in this lowermost part of the ionosphere which is
further modulated by geomagnetic activity. In addition, the diurnal occurrence pattern over
altitude provides evidence for a relation of these echoes to tidal downward phase propagation.
This is further scrutinized by comparison of the diurnal echo morphology to the
corresponding morphology of tidal wind structures in the same altitude range as observed
with collocated MF-radars. The same MF-radar observations are further used to
investigate the frequency dependence of the observed echoes promising insight
into the underlying scattering mechanism. This is important since the scattering
mechanism is currently debated between two major hypotheses. One of these is invoking
infrasound propagation and viscosity waves and the other is proposing neutral air
turbulence as the main physical process creating these echoes. Finally, we also present
some first multi-beam observations of these echoes which allow us to determine
their horizontal structure and study their relation to horizontal wave propagation. |
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