Changes of the global ionosphere during the last two solar cycles

Abstract

The solar activity during the last solar minimum period between the cycles 23 and 24 was anomalously low and lasted long compared with previous solar minimum condition. The resulting solar irradiance received in the Earths upper atmosphere was extremely low and therefore it can readily be expected that the upper atmosphere should be greatly affected by this low solar activity. There were several studies on this effect but many of them was on the thermosphere (Solomon et al., 2010

Emmert et al., 2010). According to these studies, the thermospheric temperature was cooler and the density was lower than the previous solar minimum periods. The low solar irradiance during the last solar minimum should also affect the ionosphere, not only via the lower ion-electron production due to the lower EUV radiation but also through the interactions with the thermosphere. In this study, we utilized the measurements of total electron content from the TOPEX and JASON satellites during the periods of 1992 to 2010, which includes the last two solar minimums, in order to investigate the differences between the ionospheric behaviors during the two minimum conditions. Initially the levels of the global ionization will be examined during these minimum periods and then further discussions will be continued on the details of the ionospheric behavior such as the seasonal and storm-time variations.