scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...
scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...
scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...
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STP12 Abstracts<br />
Berlin, 12 - 16 July <strong>2010</strong><br />
SCOSTEP Symposium <strong>2010</strong><br />
General Circulation Ch<strong>an</strong>ges Seen in the Mesosphere<br />
Offerm<strong>an</strong>n Dirk 1 , Hoffm<strong>an</strong>n Peter 2 , Knieling Peter 3 , Koppm<strong>an</strong>n Ralf 4 , Oberheide Jens 5 , Steinbrecht<br />
Wolfg<strong>an</strong>g 6<br />
1 Physics Dept. Univ.Wuppertal, 2 Inst.Atm.Phys., Kühlungsborn, 3 Physics Dept. Univ. Wuppertal, 4<br />
Physics Dept.Univ.Wuppertal, 5 Dept.Phys.Astron, Clemson Univ., 6 Met.Obs.Hohenpeißenberg,<br />
DWD<br />
Temperature measurements at two OH stations (Wuppertal, 51°N, 7°E; Hohenpeißenberg,<br />
48°N, 11°E) cover almost two solar cycles (#22, #23) <strong>an</strong>d are <strong>an</strong>alyzed for long-term trends<br />
<strong>an</strong>d solar influences on <strong>an</strong> <strong>an</strong>nual basis.<br />
The seasonal variations of OH temperatures ( high values during winter, low values during<br />
summer) are counter-intuitive <strong>an</strong>d are closely linked to the atmospheric circulation. The width<br />
of the “summer-valley” is monitored for long-term ch<strong>an</strong>ges by me<strong>an</strong>s of the “Equivalent<br />
Summer Duration” (ESD) which is defined as the time sp<strong>an</strong> with temperatures lower th<strong>an</strong><br />
198 K. A long-term increase of ESD is found with a rate of about one day per year.<br />
Temperature trends have also been <strong>an</strong>alyzed on a monthly basis. They are quite different in<br />
different parts of the year which explains the ESD trend. Summer duration in the stratosphere<br />
has been determined from zonal wind turn-around in spring <strong>an</strong>d autumn. A long-term ch<strong>an</strong>ge<br />
is observed here, too. Its sign is, however, opposite to that in the mesosphere, i.e. summer<br />
duration becomes shorter. These summer length ch<strong>an</strong>ges are interpreted as long-term ch<strong>an</strong>ges<br />
of middle atmosphere general circulation. They appear to be linked to ch<strong>an</strong>ges of the<br />
Eliassen-Palm flux from the troposphere to the lower stratosphere.<br />
Recent <strong>an</strong>alyses of Quasi Two-Day Waves (QTDW) in the summer mesosphere have found<br />
a triple maximum of amplitudes. This triplet has ch<strong>an</strong>ged its form during the last 21 years.<br />
Thus the dynamical stability of the mesosphere has ch<strong>an</strong>ged. This is supported by<br />
corresponding ch<strong>an</strong>ges of the baroclinic instability that has been <strong>der</strong>ived from wind<br />
measurements at Juliusruh (54°N, 13°E). In summary there are quite a number of different<br />
parameters measured by different methods <strong>an</strong>d at different altitudes that consistently support<br />
the idea of a circulation ch<strong>an</strong>ge in the mesosphere.
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