Characterizing Magnetic Clouds Associated with Solar Coronal Mass Ejections through in situ Observations

Abstract

Coronal mass ejections (CMEs) are occasional expulsions of plasma and magnetic fields from the solar corona. It is well-known that Earth-directed CMEs are the primary drivers of geomagnetic storms that lead to space weather disturbances in the near-Earth space environment like the magnetosphere and ionosphere. We rely on a wide range of technologies in response to such disturbances in space weather. Astronauts are also affected by the radiation from solar energetic particles. A thorough understanding of CME dynamics and realistic estimates of Sun-Earth CME propagation times are therefore very crucial for space weather forecasting. In situ measurements of plasma parameters by near-Earth satellites provide detailed information on CME interiors along the line of intercept of the spacecraft. We analyze and interpret such data for a large number of well-observed Earth-directed CMEs in my thesis..

CMEs are well-known to expand as they propagate through the heliosphere. However, their cross-sections are usually modeled as static plasma columns under the framework of ideal magnetohydrodynamics (MHD). We test the validity of these assumptions for CME plasma. We find that the Joule heating rate is too low to meet the required heating budget inside CMEs. We also study the amplitude of turbulent fluctuations in the proton density and total magnetic field for a large sample of near-Earth CMEs. We find that the velocity fluctuations inside and at the boundaries of CMEs are subsonic in nature. Our results show that the anomalous resistivity coming from the electrons scattering due to magnetic field turbulence is significantly higher than the Spitzer resistivity in the CME plasma. In CMEs, such enhanced resistivity may supplement Joule heating. The pressure and specific energy of CME plasma are assumed to play a key role in governing the dynamics of CMEs during their propagation through the solar wind. We estimate the total specific energy (comprising kinetic, thermal, and magnetic field contributions) inside near-Earth CMEs and compare it with the ambient solar wind background. We also examine if the excess thermal+magnetic specific energy in CMEs might make them resemble rigid objects in the context of CME aerodynamic drag.