Investigating Turbulent Fluctuations in ICME Regions Using Wavelet Analysis

Abstract

This thesis investigates the internal structure of Coronal Mass Ejections (CMEs). CMEs directed towards Earth, known as Interplanetary Coronal Mass Ejections (ICMEs), are major drivers of geomagnetic storms—disturbances in Earth’s magnetosphere caused by enhanced solar wind energy input that can severely impact satellites, power grids, and communication systems. CMEs can generally be classified into three regions: the shock/sheath, the magnetic cloud (MC), and the background solar wind. The sheath is the compressed plasma between the shock front and the MC, playing a key role in triggering and modulating geomagnetic storms through its interaction with Earth’s magnetosphere. Turbulence in the sheath and MC is manifested as intermittent, high-frequency fluctuations in plasma parameters. These turbulent spots indicate localized energy dissipation and proton heating, and their intensity and occurrence help reveal structural differences between CME regions. Previous studies have attempted to characterize CMEs by comparing the power contained in high-frequency turbulent fluctuations across the sheath, MC, and background solar wind using Power Spectral Density (PSD). In this work, we employ a wavelet-based approach to detect and quantify turbulent spots using near-Earth in-situ observations from NASA’s Wind spacecraft for a sample of 125 ICMEs. Real-time identification of the sheath or leading ICME region remains a significant challenge for space weather forecasting. Existing classification approaches, which rely primarily on bulk variations in the magnetic field (B), velocity (V), and proton density (n), do not adequately capture the intermittent turbulent character of these regions. We demonstrate that the intensity and occurrence rate of turbulent spots serve as unique and reliable indicators to distinguish the structural layers of an ICME and highlight potential sites of enhanced proton heating.