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Abstract

Here we give an update on the long-term evolution of the annual mean OH*(3,1) rotational temperatures observed from Wuppertal, which cover now the time interval 1988 - 2022. The long-term evolution is characterized by two components. Firstly, we derived a significant correlation of the temperatures and the F10.7 cm solar radio flux with a sensitivity of 4.8 ± 0.7 K/(100 SFU). Then we show that the second major component is a significant long-periodic oscillation. The observed oscillation has a period of P = 22.2 ± 1.5 years with an amplitude A = 1.8 ± 0.4 K. Because of the shorter length of the time series in the previous study concerning the long-term evolution (1988 - 2015), a trend-break in mid-2000s (negative linear trend before and positive after break point) was an option to describe the time series at that point. This trend-break is no longer an option, since the time series is now long enough to clearly identify the long-periodic oscillation. In contrast to many other studies, a significant linear trend cannot be derived for the Wuppertal OH*(3,1) rotational temperatures. The long-periodic oscillation has a large influence on the derivation of linear trends depending on the analyzed time interval. This explains the different linear trends that have been derived in past studies for this time series (in the range from -2.3 to -0.9 K/decade), because different parts of the time series and, therefore, different parts of the oscillation (e.g mainly downswing or a complete cycle) have been analyzed.