Investigation of the Forces that Govern the Three-Dimensional Propagation and Expansion of Coronal Mass Ejections from Sun to Earth

Abstract

In the last few decades, we have discovered that the environment of our solar system is as dynamic as terrestrial weather. The source of space weather is the Sun which produces winds and storms that effect modern human systems. The most geo-effective aspect of space weather is Coronal Mass Ejections (CMEs) which are analogous to terrestrial hurricanes. These powerful storms, comprised of plasma and magnetic fields, can significantly disrupt Earth's magnetic field and cause a range of terrestrial effects from the aurora to the destruction of technological infrastructure. It is only recently that we have been able to continuously monitor CMEs as they progress from the Sun to Earth. Even with continuous monitoring with remote sensing observations, we are still unable to accurately predict the arrival or terrestrial impact of a CME. There is much about the evolution of CMEs we do not understand. In this study, we analyze nine CMEs from the Sun to Earth as observed in both the remote sensing and in situ data sets. To date, this is the largest study of Earth impacting CMEs using the multi-view point remote sensing and in situ data. However, the remote sensing and in situ data of the same CME cannot be directly compared. Thus, we use several models to parameterize the two data sets. We are able to compare the arrival time, Earth impact speed, internal magnetic field, size and orientation as derived from the remote sensing and in situ methods. By comparing these results, we hope to gain a more comprehensive understanding of the inner heliospheric evolution of CMEs. In this study, we track CMEs from the Sun to 70% - 98% of the distance to Earth with the remote sensing data. We analyze the propagation and expansion of the CMEs by applying two geometric models of their structure. From the derived kinematics, we compare the predicted arrival times and impact velocities with the in situ data. We find that even with nearly continuous observations and the best available model of the CME structure, there is still a significant error in the predicted values. We discuss the possible causes of these errors. To investigate the drivers of the CME, we use the derived kinematics and mass of the CMEs to calculate the net force. We estimate the various forces acting on the CME as predicted by three theoretical models of CME propagation and expansion and compare these results with the observational results. We find that the flux rope model of Chen (1989) provides the best agreement with the observations. With the ux rope model, we are able to predict the internal magnetic field of the CME near Earth from the remote sensing data to an order of magnitude. This result is of great importance to space weather predictions since the strength of the internal magnetic field is a major factor in the geoeffectiveness of a CME. We discuss a possible method of better fitting the flux rope model to remote sensing observations with the goal of improving the accuracy of the predicted magnetic field values. Finally, we compare the size and orientation of the CMEs as predicted from the remote sensing and in situ data. We find very little agreement between the values derived from the two data sets. This aspect of the study also has large implications to space weather since the orientation of the CME's magnetic field is the other major factor in geo-effectiveness. Since the in situ data is our only source of direct information of the magnetic field and remote sensing data the main means of prediction, it is essential that the analysis of these two data sets is reconciled.