CME Parameter Input to ENLIL: LASCO halo cone versus STEREO measurements

ENLIL is a well-known model in the solar-helio community (Odstrcil and Pizzo, 1999) and is frequently used to predict the arrival of coronal mass ejections (CMEs) at Earth based on observations from the SOHO LASCO coronagraphs. The halo CME parameters needed to drive ENLIL are the CME size, speed, and direction, and these are typically derived from fitting a "cone model" to the LASCO CME images to drive interplanetary disturbances through the inner heliosphere (Xie et al., 2004). But as seen from a single vantage point along the Sun-Earth line, it is difficult to determine these projected CME parameters unambiguously (e.g., Gopalswamy et al., 2009). Over the past few years we have been in the fortunate circumstance of having the twin STEREO spacecraft (Kaiser et al., 2008) at quadrature with the Sun-Earth line, so we can compare directly the validity of the cone model with actual measurements of the CMEs heading toward Earth. We report here on a comparison of more than twenty SOHO LASCO halo coronal mass ejections that were also observed by STEREO between 2008 and mid-2011.