Comparison of Interplanetary Disturbances at theNEARSpacecraft with Coronal Mass Ejections at the Sun

Abstract

We examined interplanetary (IP) magnetic field disturbances recorded by the Near Earth Asteroid Rendezvous-Shoemaker spacecraft (NEAR) when it was above either the east or west solar limb as seen from Earth; we then identified the associated coronal mass ejections (CMEs) detected above the limbs by the SOHO LASCO coronagraph. We found 10 cases in which a nonrecurring IP disturbance could be associated with a CME. Eight of the disturbances included a magnetic flux rope signature. Flux rope chirality and axis orientation were determined for each one and compared with chirality and axis orientation at the Sun, as inferred from flux rope signatures—filaments and sigmoids—that could be associated with the CMEs. In most cases, the chirality and orientation inferred from these preeruption flux rope signatures agreed well with the flux rope signatures at NEAR. These results suggest, in agreement with Plunkett and coworkers, that the flux ropes existed prior to eruption and that the flux ropes on the Sun become flux ropes in IP space. Comparisons of the CME speeds to the time-of-flight average speeds showed that flux ropes are less accelerated or decelerated by the solar wind than are the CME leading edges. These results imply that the faint features or loops that make up the CME leading edges are probably distinct from the flux ropes.