No long term change of the thermal structure in the mesosphere at high latitudes during summer

Abstract

In the 1960s a total of 21 rocket-grenade (RG) temperature soundings have been performed in the mesosphere at high latitudes (∼70°N) in summer, 6 flights at Kronogård (66°N) and 15 at Point Barrow (71°N). These ‘historical’ data are compared with a compilation of falling sphere measurements performed in the last ∼10 years from the Andøya Rocket Range (69°N). The difference between ‘old’ and ‘new’ temperatures is very small and is compatible with zero. This suggests that there is no significant change of the thermal structure in the polar summer mesosphere during the last ∼35 years. A detailed analysis shows that a solar cycle influence on the temperature differences is very unlikely since most measurements were performed during the same phase of the solar cycle (i. e., at small activity). Considering natural variability and instrumental uncertainties we find no significant temperature trend in the altitude of interest here (50–85 km). This result is true for both RG stations located at rather different longitudes. In the lower (upper) mesosphere at 50–60 km (75–85 km) we find a small but not significant positive (negative) temperature trend of +0.06±0.02 K/y (−0.09±0.03 K/y). These numbers are much smaller in absolute magnitude compared to temperature trends observed at middle latitudes by lidars and rocket-borne techniques. Our numbers are also much smaller compared to the very large (negative) values of up to −1.2 K/y recently reported from the middle mesosphere at very high latitudes of 81°N (Golitsyn et al., 1996). We note, however, that the instrumental uncertainty of the technique involved there (rocket-borne thermistors) increases to unacceptably large values in the middle and upper mesosphere.