Critical frequencies of the ionospheric $F_1$ and $F_2$ layers during the last four solar cycles: sunspot group type dependencies

TL;DR

This study analyzes the long-term dependencies of ionospheric F$_1$ and F$_2$ critical frequencies on solar activity, revealing different sensitivities to sunspot group sizes and their implications for space weather understanding.

Contribution

It uncovers distinct solar activity dependencies of F$_1$ and F$_2$ layers based on sunspot group sizes, offering new insights into ionosphere responses to space weather.

Findings

F$_1$ critical frequency peaks with small sunspot groups.

F$_2$ critical frequency peaks with large sunspot groups.

F$_2$ layer is more sensitive to CMEs and fast solar winds.

Abstract

The long term solar activity dependencies of ionospheric F$_1$ and F$_2$ regions' critical frequencies ($f_0F_1$ and $f_0F_2$) are analyzed for the last four solar cycles (1976--2015). We show that the ionospheric F$_1$ and F$_2$ regions have different solar activity dependencies in terms of the sunspot group (SG) numbers: F$_1$ region critical frequency ($f_0F_1$) peaks at the same time with the small SG numbers, while the $f_0F_2$ reaches its maximum at the same time with the large SG numbers, especially during the solar cycle 23. The observed differences in the sensitivity of ionospheric critical frequencies to sunspot group (SG) numbers provide a new insight into the solar activity effects on the ionosphere and space weather. While the F$_1$ layer is influenced by the slow solar wind, which is largely associated with small SGs, the ionospheric F$_2$ layer is more sensitive to Coronal Mass Ejections (CMEs) and fast solar winds, which are mainly produced by large SGs and coronal holes. The SG numbers maximize during of peak of the solar cycle and the number of coronal holes peaks during the sunspot declining phase. During solar minimum there are relatively less large SGs, hence reduced CME and flare activity. These results provide a new perspective for assessing how the different regions of the ionosphere respond to space weather effects.