The paper explains why the solar activity index F30 is more suitable for ionospheric and thermospheric long-term trends.

The topic of long-term changes and trends in the upper atmosphere, since Roble and Dickinson's seminal 1989 paper, remains relevant and current with ongoing controversies. Some of these issues have been resolved over time, while others have become even more controversial. This paper makes a significant contribution to this important topic. The authors have demonstrated that at least one of the widely used established empirical formulae for the ionospheric peak height, hmF2, introduces diurnal, seasonal, and long-term biases into hmF2 estimates. These biases are of similar, if not greater, magnitude than those expected from the long-term cooling resulting from increased greenhouse gases concentration.

The study is devoted to a shock auroral event that occurred on February 26, 2023, in northern Scandinavia, and represents the first time such nighttime auroral features have been captured by ground-based cameras. Shock auroras result from a very specific driving impulse in the solar wind. While the primary effects appear on the dayside of the Earth, the authors succeeded in observing the nightside signatures, which are rare and difficult to detect. The study is a successful scientific achievement as it presents newly discovered phenomena that provide new insights into solar wind interactions with the nightside ionosphere.