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| Titel |
Radar cross sections for mesospheric echoes at Jicamarca |
| VerfasserIn |
G. A. Lehmacher, E. Kudeki, A. Akgiray, L. Guo, P. Reyes, J. Chau |
| 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 ; 27, no. 7 ; Nr. 27, no. 7 (2009-07-06), S.2675-2684 |
| Datensatznummer |
250016580
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2675-2009.pdf |
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| Zusammenfassung |
| Radar cross sections (RCS) of mesospheric layers at 50 MHz observed at
Jicamarca, Peru, range from 10−18 to 10−16 m−1, three orders
of magnitudes smaller than cross sections reported for polar mesospheric
winter echoes during solar proton events and six orders of magnitude smaller
than polar mesospheric summer echoes. Large RCS are found in thick layers
around 70 km that also show wide radar spectra, which is interpreted as
turbulent broadening. For typical atmospheric and ionospheric conditions,
volume scattering RCS for stationary, homogeneous, isotropic turbulence at 3 m
are also in the range 10−18 to 10−16 m−1, in reasonable
agreement with measurements. Moreover, theory predicts maximum cross
sections around 70 km, also in agreement with observations. Theoretical
values are still a matter of order-of-magnitude estimation, since the Bragg
scale of 3 m is near or inside the viscous subrange, where the form of
the turbulence spectrum is not well known. In addition, steep electron
density gradients can increase cross-sections significantly. For thin layers
with large RCS and narrow spectra, isotropic turbulence theory fails and
scattering or reflection from anisotropic irregularities may gain relevance. |
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