Mathematisch-Naturwissenschaftliche Fakultät

Institut für Atmosphärenphysik

Fachgebiet: Atmosphärenphysik

Betreuer: Prof. Dr. Franz-Josef Lübken

Diplom-Meteorologe Olof Zeller
(e-mail: )

Impact of atmospheric terms and ionization variations on mesosphere radar echoes in polar and mid latitudes

This work focusses on the impact of atmospheric terms and ionization variations on radar echoes in the mesosphere. The measurements are based on observations with the VHF radars (53.5 MHz) in Kühlungsborn (54°N) and Andenes (69°N). During summer very strong echoes occur in 80 – 92 km and during winter obviously weaker echoes in 55 – 85 km.

Mesospheric summer echoes exist generally only at temperatures below the frost point of water vapour. Particularly in mid latitudes the temperature fluctuates around this frost point and, in addition, there exists a strong meridional temperature gradient due to the vertical-meridional circulation. Under these conditions meridional wind variations caused by planetary waves are reflected well in the radar echo structures.

Enhanced ionization of the D layer leads to stronger radar echoes. Eliminating the ionization influence by a multiple regression method, a weak positive trend of the summer echoes since the mid 1990s is shown which can be caused by a negative temperature trend or a water vapour increase in the mesosphere. Both causes are important indices of climatic change and contribute to a better understanding of thermodynamic activities in the whole atmosphere.

Radar echoes occur in winter much more rarely than in summer. Investigations of winter echoes are mainly concentrated on ionization sources. Most echoes are observed during day-time whereas their occurrence is abundantly increased at periods with enhanced high energetic particle precipitation. A positive correlation between turbulent energy dissipation rate and winter echoes confirm the assumption of neutral gas turbulence as the most important source for winter echo creation.