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Ann. Geophys., 25, 1779-1790, 2007
www.ann-geophys.net/25/1779/2007/
© European Geosciences Union 2007
Long-term variations of the mesospheric wind field at mid-latitudes
D. Keuer, P. Hoffmann, W. Singer, and J. Bremer
Leibniz-Institute of Atmospheric Physics, 18225 Kühlungsborn, Schloss-Str. 6, Germany
Abstract. Continuous MF radar observations at the station Juliusruh
(54.6° N; 13.4° E) have been analysed for the time interval between
1990 and 2005, to obtain information about solar activity-induced variations, as
well as long-term trends in the mesospheric wind field. Using monthly median
values of the zonal and the meridional prevailing wind components, as well as
of the amplitude of the semidiurnal tide, regression analyses have been
carried out with a dependence on solar activity and time. The solar activity
causes a significant amplification of the zonal winds during summer
(increasing easterly winds) and winter (increasing westerly winds). The
meridional wind component is positively correlated with the solar activity
during summer but during winter the correlation is very small and
non significant. Also, the solar influence upon the amplitude of the
semidiurnal tidal component is relatively small (in dependence on height
partly positive and partly negative) and mostly non-significant.
The derived trends in the zonal wind component during summer are below an
altitude of about 83 km negative and above this height positive. During the
winter months the trends are nearly opposite compared with the trends in
summer (transition height near 86 km). The trends in the meridional wind
components are below about 85 km positive in summer (significant) and near
zero (nonsignificant) in winter; above this height during both seasons
negative trends have been detected. The trends in the semidiurnal tidal
amplitude are at all heights positive, but only partly significant.
The detected trends and solar cycle dependencies are compared with other
experimental results and model calculations. There is no full agreement
between the different results, probably caused by different measuring
techniques and evaluation methods used. Also, different heights and
observation periods investigated may contribute to the detected differences.
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