To long-term Variability of the Mesosphere over Europe

The study of long-term variability in the extra-tropical mesosphere is important for our understanding of mesospheric variability and long-term trends, cause by the coupling of atmospheric layers. Some observations and current model calculations are showing a substantial mesospheric cooling to occur and connect the temperature decrease to global tropospheric warming over the last decades. For the mesosphere long-term measurements are seldom. The indirect LF- phase height measurement of electron density at Kühlungsborn (54° N, 12° E) for a height of about 82 km was started in February 1959 and run over 50 years without any large breaks. In this study of long-term variability we use a 49 yrs data set of daily heights for a constant level of electron density and scale height over Europe. The calculated spectra show beside a strong annual and semiannual cycle, peaks for a 30 months period, a 3.4 yrs-, a 5 yrs-, and a 9 yrs period. Due to the strong coupling between atmospheric layers of stratosphere and mesosphere, a dynamical origin of some typical periods of long-term variability is assumed and has been examined by using northern hemispheric data from ERA 40 reanalysis of ECMWF. For instance, for the 30 months period we found a strong correlation with the quasi-biennial oscillation of the subtropics of the stratosphere, which implies a dynamical relationship. An estimation of the annual mean thickness temperature trend for the lower mesosphere results in a -3K decrease per decade. A comparison with long-term LIDAR measurements is presented as well as a possible explanation due to the change of ultra-long wave structure.