The formation of polar mesospheric clouds (PMCs) depends on water vapor and cold temperatures in summer. Since the end of 1950s, that means over more than 5 solar cycles, field strength measurements of the broadcasting station, Allouis (Central France), have been performed at Kühlungsborn (54° N, 12° E, Mecklenburg, Northern Germany. These so-called indirect phase-height measurements of low frequency radio waves (here with a frequency of 162 kHz) are used to study the long-term variability and trends of the mesosphere over Europe. The advantages of the method are the low costs and the simplicity of operation. The reanalyzed forth release of standard-phase height measurements (SPH-R4) with a loss rate below 10% is presented and discussed for summer months.

The plasma-scale height is used as a proxy for mean temperature variability of the upper mesosphere and the calculated thickness-temperature is used as proxy for the column-integrated mesospheric temperature. The derived thickness-temperature of the mesosphere decreased statistically significant over the period 1959-2017 after pre-whitening with summer means of solar sun spot numbers. The trend value is in the order of about -1 K/ decade if the stratopause trend is excluded. The linear regression with time is stronger for the period of 1963-1985 (2 SCs), but 2.6 times weaker during 1986-08 (next 2 SCs). The upper mesospheric temperature derived from plasma-scale height shows no significant change in summer. Furthermore the influence of solar variability on mesospheric temperatures is discussed.