Observational evidence for a quasi-bidecadal oscillation in the summer mesopause region over Western Europe

We analyzed plasma scale height observations (about 80 km altitude) over the Eifel region (50°N, 6°E) observed from Kühlungsborn (54°N, 12°E) in the time interval 1959-2016 and OH* temperatures (center altitude 87 km) observed from Wuppertal (51°N, 7°E) in the time interval 1988-2016. In summer months both time series show a dominant oscillation with a period of about two decades (20-26 years) with amplitudes of about 180 m and 3 K, respectively. These two oscillations are anticorrelated, because their observation altitudes are located above and below the temperature minimum in the mesopause region in summer, i.e. in a region of a positive and negative temperature gradient, respectively. We assume that a periodic vertical displacement of the mean temperature profile (upward and downward shifts following each other) in long-term variability leads to such an anticorrelated temperature evolution at the different observation altitudes. This mechanism is confirmed by SABER observation on board the TIMED satellite.