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| Titel |
The Turbopause experiment: atmospheric stability and turbulent structure spanning the turbopause altitude |
| VerfasserIn |
G. A. Lehmacher, T. D. Scott, M. F. Larsen, S. G. Bilén, C. L. Croskey, J. D. Mitchell, M. Rapp, F.-J. Lübken, R. L. Collins |
| 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 ; 29, no. 12 ; Nr. 29, no. 12 (2011-12-23), S.2327-2339 |
| Datensatznummer |
250017149
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| Publikation (Nr.) |
 copernicus.org/angeo-29-2327-2011.pdf |
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| Zusammenfassung |
| Very few sequences of high resolution wind and temperature measurements in
the lower thermosphere are available in the literature, which makes it
difficult to verify the simulation results of models that would provide
better understanding of the complex dynamics of the region. To address this
problem the Turbopause experiment used four rockets launched over a period of
approximately two hours from Poker Flat Research Range, Alaska (64° N,
147° W) on the night of 17–18 February 2009. All four rocket payloads
released trimethyl aluminum trails for neutral wind and turbulence
measurements, and two of the rockets carried ionization gauges and fixed-bias
Langmuir probes measuring neutral and electron densities, small-scale
fluctuations and neutral temperatures. Two lidars monitored temperature
structure and sodium densities. The observations were made under quiet
geomagnetic conditions and show persistence in the wind magnitudes and shears
throughout the observing period while being modulated by inertia-gravity
waves. High resolution temperature profiles show the winter polar mesosphere
and lower thermosphere in a state of relatively low stability with several
quasi-adiabatic layers between 74 and 103 km. Temperature and wind data were
combined to calculate Richardson number profiles. Evidence for turbulence
comes from simultaneous observations of density fluctuations and downward
transport of sodium in a mixed layer near 75 km; the observation of turbulent
fluctuations and energy dissipation from 87–90 km; and fast and irregular
trail expansion at 90–93 km, and especially between 95 to 103 km. The
regions of turbulent trails agree well with regions of quasi-adiabatic
temperature gradients. Above 103 km, trail diffusion was mainly laminar;
however, unusual features and vortices in the trail diffusion were observed
up to 118 km that have not been as prevalent or as clearly evident in earlier
trail releases. |
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