Coronal Flattening Index of Total Solar Eclipse on 20 April 2023 and the Prediction of Solar Cycle 25 Maximum

Abstract We observed a total solar eclipse (TSE) on 20 April 2023 in Timor Leste and analyzed the isophote of the coronal image. We obtained a coronal flattening index (ε) with a value of 0.10 and a phase value (Φ) of 0.70, indicating that the TSE had a pre-maximum coronal type. Based on the composite image of the corona, four large streamers were observed in the northern and southern hemispheres of the Sun, with small streamers scattered uniformly in the solar disk. It indicates that the Sun was in the ascending phase of its activity cycle. Moreover, we developed two models to predict the maximum of the current solar cycle (Wmax) using the Smoothed Sunspot Number (SSN) and ε from all TSE data during the ascending phase (positive Φ) from 1893 to 2013. We used Multi Linear Correlation (MLC) and 2nd-order Polynomial Regression (PR2) to predict the value of Wmax for the solar cycle 25 (SC 25) based on the observations of TSE on 20 April 2023. We obtained values of 175.5 ± 27.9 and 168.2 ± 25.8 using MLC and PR2, respectively, with the estimated peak time in September 2024. These results indicate that SC 25 will be stronger than the solar cycle 24 (SC 24).