Solar influence on the long-term change in the ionosphere

ANA G. ELIAS

Oulu

Simposio; Space Climate 5 Symposium; 2013

Oulu University

The study of long-term trends in the upper atmosphere has gained interest since the early 1990?s as a consequence of the great concern about the global warming observed in the troposphere. Since then it has become a significant topic in global change investigations.Some research works link these trends to the increase in greenhouse gases concentration, and others to natural causes such as solar and geomagnetic activity long-term changes, and secular variations in the Earth?s main magnetic field. Based on many observational and model results a global pattern of trend emerged with the dominant driver of upper atmosphere trends being the increasing concentration of greenhouse gases. At the same time, it became increasingly clear that other drivers also play an important role in long-term trends in the upper atmosphere and ionosphere. Solar activity, which is one of these drivers, will be analyzed in the present work. One possible mechanism through which solar activity may induce trends in the ionosphere is through long-term variations in the solar radiation range responsible for ionization in the ionosphere. Another mechanism is the difference in the upper atmosphere response to the different phases of the solar cycle. In fact trends may be quantitatively different under solar activity maximum and minimum conditions, which is the case for thermospheric density. In addition, different corrections to solar activity are one of the sources of differences between trend results in F2-region parameters, however in this case solar activity itself has no direct effect on observed ionospheric trends. A theoretical as well as an experimental analysis will be presented in order to determine to which extent the sun is responsible for the observed trends in the ionosphere in the context of other trend sources. The quantification of natural effects on trends is an important contribution to one of the present focus of climate science that is the determination of the extent to which human activities are altering the planetary energy balance.