Standard-Phase-height measurements over Europe during 60 years of measurements – Long-term variability and trends of the mesosphere

Beginning with 1959 that means over more than 60 years, field strength measurements of the broadcasting station, Allouis (Central France), have been carried out 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 examine the long-term evolution and trends of the mesosphere over Europe. The advantages of the method are the low costs and the simplicity of operation. The extended reanalyzed fifth release of standard-phase height (SPH) are presented.

The SPH-series are anti-correlated to the solar cycle as known because stronger photo-ionization is linked with higher number of electrons, which reduces the SPH. The anti-correlation between SPH and proxies of solar cycle are well established. Furthermore the statistical analysis of the SPH-series shows a significant overall trend in the order of hundred meters per decade induced by a shrinking stratosphere due to global warming. Strong intra-decadal variability is related to QBO like and ENSO like variability. The derived thickness temperature of the mesosphere decreased statistically significant over the period 1959-2019 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 amount of linear regression is weaker, -0.8 K/ decade for the period of 1963-1985 (2 SCs), but stronger, about -1.6 K/ decade during 1995-2016 (last 2 SCs).