Model-based analysis of ionospheric reaction to 27-day solar EUV variability - A long-term study

Abstract

Solar extreme ultraviolet (EUV) variability is a key driver of upper atmosphere ionization and as such has significant influence on ionospheric electron density and composition across multiple timescales. The 27-day solar rotation cycle is also reflected in the emitted EUV radiation and therefore also in many ionospheric parameters, such as total electron content (TEC). Superimposed on this pattern are additional long- and short-term trends and disturbances that further modulate the ionospheric plasma. This study uses numerical simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), to examine the ionospheric response to various 27-day solar rotation periods and the response of the upper atmosphere. The Open Time-Series of the High-Resolution Ionosphere-Thermosphere Aeronomic Climate Simulation (OTHITACS) dataset is used, which is based on TIE-GCM. The OTHITACS dataset allows the analysis of ionospheric responses from 2000 to 2022 under varying solar activity levels and geomagnetic states. This study mainly focuses both on global and local TEC variations. Despite irregularities in the EUV profiles, a dominance of the 27-day rotation in the ionospheric plasma is observed, which was also demonstrated in previous studies on the delayed response. Furthermore, this study provides a 4D-analysis of the ionospheric reaction to solar EUV variability.