Date of Award

Fall 2026

Abstract

In this thesis, we construct a database of coronal mass ejections (CMEs) observed by Windand STEREO-A between January 2022 and May 2025, near the maximum of Solar Cycle 25. During this interval, STEREO-A moved from 35◦ east to 35◦ west of the Sun–Earth line, providing a unique opportunity to investigate the longitudinal extent of CMEs near 1 au. A total of 106 CMEs were identified, of which only 39 events (∼ 37%) were detected by both spacecraft. The probability of simultaneous detection decreases rapidly with increasing angular separation, dropping to about 50% at separations of 14◦—20◦. These results suggest that the average full longitudinal extent of magnetic ejecta near 1 au is approximately 20◦- –30◦. Using this multi-point dataset, we examine how CME properties vary across different longitudinal sections of the same event. For CMEs observed at both spacecraft, we com- pare magnetic field strength, proton speed, radial size, and the characteristics of associated shocks and sheaths. The average magnetic field and proton speed remain consistent be- tween spacecraft, indicating that these quantities reflect coherent global properties of the ejecta. In contrast, radial size, expansion signatures, and sheath thickness exhibit substan- tial variability. To better quantify similarities between spacecraft observations, we analyze simultaneously detected events using Pearson correlation and root mean square error met- rics applied to magnetic field and bulk speed time series. While individual magnetic field components in the sheath and ejecta show weak correspondence, the total magnetic field magnitude and bulk speed within the magnetic ejecta are strongly correlated, reinforcing their large-scale coherence. We further investigate CME geometry and propagation by determining shock and ejecta front normals and by estimating the CME nose direction using multiple methods. The shock front is found to be approximately spherical with a larger radius of curvature than the ejecta, whose geometry is more variable. Sheath thickness varies significantly, even at small spacecraft separations. Nose-direction estimates using various methods indicate an eastward deflection of CMEs during propagation from the Sun to 1 au. Based on these results, we propose a revised conceptual picture of the CME three-part structure—shock, sheath, and magnetic ejecta—that better represents the events in our database. Overall, this study demonstrates the value of multi-spacecraft observations in constrain- ing CME longitudinal extent, internal coherence, and global geometry, with implications for improving space weather modeling and forecasting.

Document Type

Dissertation

First Advisor

Noe Lugaz

Second Advisor

Noe Lugaz

Third Advisor

Nada Al-haddad

Department or Program

Physics

Degree Name

Doctor of Philosophy

Download

Share

COinS