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| Titel |
VHF radar observations of turbulent structures in the polar mesopause region |
| VerfasserIn |
P. Czechowsky, R. Rüster |
| 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 ; 15, no. 8 ; Nr. 15, no. 8, S.1028-1036 |
| Datensatznummer |
250012911
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| Publikation (Nr.) |
 copernicus.org/angeo-15-1028-1997.pdf |
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| Zusammenfassung |
| The mobile SOUSY VHF Radar was operated in
the summer of 1987 during the MAC/SINE campaign in northern Norway to study the
polar mesosphere summer echoes (PMSE). Measurements of the spectral width
indicate that two types of structures occur. In general mesospheric layers are
bifurcated exhibiting a narrow spectral width and a well-defined aspect
sensitivity. However, for about 10% of the observation time cells of enhanced
turbulence characterized by extremely broad spectral widths appear predominantly
in the upper sublayer above 86 km. Identification and separation of beam and
shear broadening allows a determination of the turbulence-induced component of
the spectral width. This case study reveals that during several events these
cloud-like structures of enhanced turbulence move with an apparent velocity of
several tens of meters per second which is almost identical with the phase trace
velocity of simultaneously observed waves. Since, at that time, the Richardson
number was less than a quarter, it was concluded that these turbulent cells were
generated by a Kelvin-Helmholtz mechanism. The horizontal extent of these
structures was calculated to be less than 40 km. A general relation between
spectral width and echo power was not detected. The turbulent component of the
spectral width was used to calculate typical values of the energy dissipation
rate at times where narrow spectral width dominates and during periods of
enhanced turbulence. In addition, the outer scale of the inertial subrange
(buoyancy scale) was estimated. For the first time the occurrence and motion of
this type of structures of enhanced spectral width is analyzed and discussed in
detail. |
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