Ionospheric response to solar extreme ultraviolet radiation variations: comparison based on CTIPe model simulations and satellite measurements

Rajesh Vaishnav,Christoph Jacobi,Jens Berdermann,Mihail Codrescu,Erik Schmölter

doi:10.5194/angeo-39-341-2021

Abstract

Abstract. The ionospheric total electron content (TEC) provided by the International GNSS Service (IGS) and the TEC simulated by the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model have been used to investigate the delayed ionospheric response against solar flux and its trend during the years 2011 to 2013. The analysis of the distinct low-latitude and midlatitude TEC response over 15∘ E shows a better correlation of observed TEC and the solar radio flux index F10.7 in the Southern Hemisphere compared to the Northern Hemisphere. Thus, a significant hemispheric asymmetry is observed. The ionospheric delay estimated using model-simulated TEC is in good agreement with the delay estimated for observed TEC against the flux measured by the Solar Dynamics Observatory (SDO) extreme ultraviolet (EUV) Variability Experiment (EVE). The average delay for the observed (modeled) TEC is 17(16) h. The average delay calculated for observed and modeled TEC is 1 and 2 h longer in the Southern Hemisphere compared to the Northern Hemisphere. Furthermore, the observed TEC is compared with the modeled TEC simulated using the SOLAR2000 and EUVAC flux models within CTIPe over northern and southern hemispheric grid points. The analysis suggests that TEC simulated using the SOLAR2000 flux model overestimates the observed TEC, which is not the case when using the EUVAC flux model.

Highlights

The ionospheric day-to-day variations are mainly controlled by fluctuations of solar extreme ultraviolet/ultraviolet (EUV/UV) radiation responsible for photoionization and photo-dissociation processes, lower atmospheric forcing, and space weather events such as geomagnetic storms
The ionospheric delay estimated using model-simulated total electron content (TEC) is in good agreement with the delay estimated for observed TEC against the flux measured by the Solar Dynamics Observatory (SDO) extreme ultraviolet (EUV) Variability Experiment (EVE)
In this study we have addressed the following points: 1. The TEC variations at moderate solar activity of solar cycle 24 are analyzed to compare the input for the delay analysis

Summary

Introduction

The ionospheric day-to-day variations are mainly controlled by fluctuations of solar extreme ultraviolet/ultraviolet (EUV/UV) radiation responsible for photoionization and photo-dissociation processes, lower atmospheric forcing, and space weather events such as geomagnetic storms. The solar radiation flux varies at different timescales, including the diurnal cycle, the 27 d solar rotation period, and the prominent 11-year solar cycle. This results in corresponding variations in composition and dynamics of the thermosphere–ionosphere (T–I) system (Hedin, 1984). The photoionization processes in the ionosphere cause different variations, including short-term variability at the timescale of the 27 d solar rotation or seasonal variations. Past studies on the effect of solar radiation variations at different timescales have been based on the total electron content (TEC, frequently given in TECU; 1 TECU= 1016 electrons m−2), peak electron density (NmF2, cm−3), and the corresponding height (HmF2, km)

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