PhD Dissertation Defense Announcement Notification

Final Doctoral Defense for:  Negessa Tilahun Shukure

Department: Astronomy and Astrophysics Research and Development  

Program: Solar Astrophysics

DATE: September, 24,2021

TIME: 2:00pm

Venue : ESSTI’s new office

Supervisor: Solomon B. Tessema (Assoc. Prof.)

Co-supervisor: Prof. Natchimuthuk Gopalswamy

DISSERTATION TITLE:  “Evaluating the Long-term Stability of Total Solar Irradiance by Space Experiments and Analytical Modeling


The Sun is the major energy source of our planet. The TSI is the net energy from the Sun that strikes Earth, which is not stable over short and long timescales. The longer timescale variation, which is observed over days to the evolutionary timescale, is the interest of this study. In this thesis, we studied the TSI variability in the rotational and evolutionary timescales and its influence on the Ts. We introduced, the new empirically modeled indices defined as SFD and WFD, which use solar surface magnetic fluxes data from SDO/HMI as an input. We studied their connection with TSI data taken from SOHO/VIRGO instrument in the rotational timescale. The SSA data from NOAA is also applied to test our model. We also introduced an analytical model of TSI in the evolutionary timescale and studied its link with Ts. We first produced the SFDs and WFDs for three different thresholds: 600 G, 800 G, and 900 G for the data sets from solar maxima (2014) and solar minima (2010). Furthermore, we used the Robust Correlation toolbox to perform correlation analysis, Correlogram, and the wavelet toolbox, specifically the CWT and the XWT. To model TSI in the evolutionary timescale, we first model mass-loss varying luminosity of the Sun, which is limited to the main-sequence lifetime. We then modify the model so that it works to both in and beyond the main-sequence. We used the luminosity model to formulate the TSI model for the lifetime of the Sun. Finally, we introduced the Ts in the same timescale by using the newly introduced TSI model and the zero-dimension climate model. At the end, the dominant cause of TSI variability in the rotational timescale is identified. The solar mass-loss in its lifetime is estimated, the fate of the Sun and the TSI variation in the evolutionary timescale is indicated, and lastly the likely fate of our planet is also predicted.

Note: You are cordially invited to attend this PhD Dissertation defense.