ABSTRACT
Nishtha Sachdevanishtha.sachdeva@students.iiserpune.ac.in
Indian Institute of Science Education and Research, Pune, India
| Title : | CME dynamics using STEREO \& LASCO observations: the relative importance of Lorentz forces and solar wind drag |
| Abstract | |
| Hot, massive blobs of plasma and magnetic fields, called Coronal Mass Ejections (CMEs) are major contributers of disturbances in the near-Earth environment, sometimes causing disruptions to space-bound technologies as well. Space weather predictions are therefore, crucially dependent on accurate understanding and modeling of the CME structure and propagation dynamics. Forces that affect CME propagation include, aerodynamic drag and driving Lorentz forces. The heliocentric distances at which these dominate is still unclear. Depending on how slow or fast a CME is travelling (with respect to the ambient solar wind), the CME is ``picked up'' or ``dragged down'' by the solar wind. The Lorentz forces are thought to be effective very early on. In our work, we attempt to quantify the relative contributions of the driving Lorentz forces and aerodynamic drag acting on CMEs. In doing so we appeal to Torus Instability model and drag based model. With the availability of extensive data from STEREO \& LASCO observations we reconstruct the 3D geometrical flux-rope structure of a set of 38 CMEs using the Graduated Cylindrical Shell Model (GCS; Thernisien et al., 2009; Thernisien, 2011). We use a microphsyical model for computing the solar wind aerodynamic drag and find that the Drag-based models typically succeed only if they are initiated at heliocentric distances as large as 12--50 Rs (in case of slow CMEs) (Sachdeva et al., 2015). We find that the Lorentz forces generally peak between 1.65 and 2.35 Rs for all CMEs. For fast CMEs, Lorentz forces become negligible in comparison to aerodynamic drag as early as 3--4 Rs. For slow CMEs, however, they become negligible only by 12--50 Rs. For these slow events, our results suggest that some of the magnetic flux might be expended in CME expansion or heating. In other words, not all of it contributes to directed propagation. Combining the effects of these two forces, our results are expected to be important in building a comprehensive physical model for understanding the Sun-Earth dynamics of CMEs. |
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