Forbush Decrease Data with a Simple Model

On October 28, 2003 an earthward-directed coronal mass ejection (CME) was observed from SOHO/LASCO imagery in conjunction with an X17 solar flare. The CME, traveling at nearly 2000 km/s, impacted the Earth on October 29, 2003 causing ground-based particle detectors to register a counting rate drop known as a Forbush decrease. In addition to affecting the rate of cosmic rays, the CME was also responsible for causing anisotropies in the direction of incidence. Data from Project GRAND, an array of proportional wire chambers, are presented during the time of this Forbush decrease. A simple model for CME propagation is proposed and we present an argument based on gyroradius that shows that a magnetic field of the radius calculated for the ejecta is sufficient to deflect energetic charged particles of an energy detectable by GRAND.