Ionospheric Response to Solar EUV Radiation Variations Using GOLD Observations and the CTIPe Model

Abstract

To understand the global response of thermospheric‐ionospheric (TI) parameters to variations in solar irradiance measurements from the Global‐Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph, solar radio flux F10.7, predictions from the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, and International Global Navigation Satellite System Service total electron content maps (TEC) have been used. Various parameters such as GOLD O/N2, O2, and the nighttime peak electron density (Nmax) have been compared with the CTIPe model simulations. The GOLD observed Nmax shows a number of significant features including a winter anomaly and an equatorial ionization anomaly. The comparison with solar proxies showed that the GOLD QEUV correlates very well with the EUV observations compared to the F10.7 index. The study also examined the relationship between the solar proxies and Nmax on different time scales and found that Nmax responded significantly to QEUV at both medium‐ and long‐term timescales. Furthermore, a low correlation between Nmax in the equatorial region and solar proxies was found. A delayed ionospheric TEC response against solar flux variations within the 27‐day solar rotation was investigated. This ionospheric delay of TEC with respect to solar flux was observed to be less than 1 day, which was reproduced in model simulations. The current study has shown that the GOLD observations can be used to investigate the delayed ionospheric response and to gain a better understanding of the influence of solar activity on the TI system.

Spatial Features of the Delayed Ionospheric Response During Low and High Solar Activity

“…The present study investigated the spatial and temporal variations of the delayed ionospheric response at different solar activity levels. The results based on F10.7 are in good agreement with preceding studies using the solar proxy for ionospheric modeling (Ren et al, 2018;Vaishnav et al, 2018Vaishnav et al, , 2019Vaishnav et al, , 2023 and are of interest, since modeling via solar flux models based on F10.7 is commonly applied. The wavelength-dependent results provide a more comprehensive insight to the various processes impacting the delayed ionospheric response.…”

“…Schmölter and von Savigny (2022) reported these differences with TIMED/SEE measurements and the present study confirms the results with SDO/EVE measurements. While an investigation with F10.7 is of interest due to the extensive use of the solar proxy for studies with ionosphere models (Ren et al, 2018;Vaishnav et al, 2018Vaishnav et al, , 2019Vaishnav et al, , 2023, the complex variability of solar EUV can only be partially reflected.…”

“…Modeling studies using the solar proxy F10.7 Vaishnav et al, 2018Vaishnav et al, , 2019 via solar flux models (e.g., EUVAC) describe spatial variations like the results based on the full spectrum (see Figure 12f) or response at wavelengths from 37 to 78 nm (see Figure 12b). Studies using the solar proxy Q EUV (Schmölter et al, 2021;Vaishnav et al, 2023), which describes the integrated solar EUV irradiance at wavelengths shorter than 45 nm (Eastes et al, 2017), or Solar and Heliospheric Observatory (SOHO) Solar EUV Monitor (SEM) measurements with two bands from 26 to 34 nm and from 0.1 to 50 nm (Judge et al, 1998) are more difficult to interpret, since these wavelength ranges integrate different features. Wavelengthdependent analyses (Schmölter & von Savigny, 2022) are complex, but offer a reference to studies using solar EUV at specific wavelength ranges.…”