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| Titel |
Mesopause jumps at Antarctic latitudes |
| VerfasserIn |
Franz-Josef Lübken, Josef Höffner, Erich Becker, Ralph Latteck, Damian Murphy |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122986
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| Publikation (Nr.) |
 EGU/EGU2016-2145.pdf |
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| Zusammenfassung |
| Recent high resolution temperature measurements by resonance lidar at Davis (69∘S)
occasionally showed a sudden mesopause altitude increase by ∼5 km and an associated
mesopause temperature decrease by ∼10 K. We present further observations which are
closely related to this ‘mesopause jump’, namely the increase of mean height of
polar mesospheric summer echoes (PMSE) observed by a VHF radar, very strong
westward winds in the upper mesosphere measured by an MF radar, and relatively large
eastward winds in the stratosphere taken from reanalysis. We compare to similar
observations in the Northern Hemisphere, namely at ALOMAR (69∘N) where such
mesopause jumps have never been observed. We present a detailed explanation of
mesopause jumps. They occur only when stratospheric winds are moderately eastward
and mesospheric winds are very large (westward). Under these conditions, gravity
waves with comparatively large eastward phase Speeds can pass the stratosphere
and propagate to the lower thermosphere because their vertical wavelengths in
the mesosphere are rather large which implies reduced dynamical stability. When
finally breaking in the lower thermosphere, these waves drive an enhanced residual
circulation that causes a cold and high-altitude mesopause. The conditions for a
mesopause jump occur only in the Southern Hemisphere (SH) and are associated with the
late breakdown of the polar vortex. Mesopause jumps are primarily, but not only,
observed prior and close to solstice. We also show that during the onset of PMSE
in the SH, stratospheric zonal winds are still eastward (up to 30 m/s), and that
the onset is not closely related to the Transition of the stratospheric circulation. |
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