Determination of geometrical and kinematical properties of halo coronal mass ejections using the cone model

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Abstract
Many broadside coronal mass ejections (CMEs) propagate almost radially beyond the first couple of solar radii, and their angular widths remain nearly constant while propagating through the corona. Assuming that these characteristics hold true for halo CMEs that originate far from solar limbs, some useful geometric and kinematic properties of halo CMEs may be reproduced using a simple geometrical model of a CME as a cone. The cone model uses three free parameters, characterizing the angular width and the central position of the halo CME. These geometric properties can be determined by matching the observed halos at a series of times with the modeled halos for a series of radial distances. The kinematic properties, the radial velocity and acceleration, of the halo CME can also be determined on the basis of the series of times and radial distances. These properties are important for predicting the geoeffectiveness of a halo CME and cannot be observed directly with currently available instrumentation. As a test, the geometric and kinematic properties of the 12 May 1997 halo CME have been inferred using the cone model. This shows that the cone model does provide a new way of testing our understanding of halo CMEs, though there are limitations for some halo CMEs.