Abstract
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.
Highlights
The first investigations of the influence of the solar activity on the wind field of the mesosphere and lower thermosphere (MLT region) were published by Sprenger and Schminder (1969), using LF wind observations at mid-latitudes from 1957 until 1968
Their correlations between the zonal wind and the solar activity were different depending on the time period investigated
If we look more carefully at the variation of the semidiurnal tidal amplitude in Fig. 21 during the second subinterval, the most dominant increase started in the year 2001
Summary
The first investigations of the influence of the solar activity on the wind field of the mesosphere and lower thermosphere (MLT region) were published by Sprenger and Schminder (1969), using LF wind observations at mid-latitudes from 1957 until 1968 They found positive correlations between solar activity and zonal as well as meridional winds during winter and a negative correlation between the amplitude of the semidiurnal tidal component and the solar activity. Greisiger et al (1987) achieved partly different results when they investigated a longer time series than that used by Sprenger and Schminder (1969), including additional meteor radar wind observations Their correlations between the zonal wind and the solar activity were different depending on the time period investigated. It was assumed that this height may be constant, in spite of the fact that due to a greenhouse cooling the middle atmosphere is shrinking (Bremer and Berger, 2002)
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