Long-term solar activity impact on ionospheric ionization

Abstract

The question, how global climate change impacts the ionosphere-thermosphere system is of fundamental interest for improving our understanding of the Earth system. Related studies, made for more than 3 decades, have shown some small effects that might be explained by the impact of the dramatic increase of trace gases like CO2 in the troposphere. The talk aims at improving methodology aspects to refine and extend the analysis of long time series of the F2 layer peak electron density NmF2 derived from observations at the three ionosonde stations Juliusruh, Boulder and Kokubunji. Starting in 1957, the data cover about 6 solar cycles. In parallel, Total Electron Content (TEC) data, available since 1996, are used to derive the equivalent slab thickness over these ionosonde stations. Attempts have been made to utilize the slab thickness for estimating the neutral gas temperature at peak density heights. The dramatic decrease of the equivalent slab thickness and the F2 layer peak electron density over the last two solar cycles is discussed in relation to the solar activity characterized by the 10.7 cm radio flux index. It is shown that the relationship of the ionospheric ionization with the solar activity changes significantly during the last 2 solar cycles.