Cosmic-ray intensity enhancement and the structure of the 1998 May 2 solarwind disturbance

The Zyganenko-89 magnetosphere model is used for disturbed geomagnetic cond itions (K-p greater than or equal to 7) to analyze the anisotropy of relati vistic solar protons (RSP) by calculating the asymptotic directions of sola r proton arrival. The conclusion is made that the unusual behavior of the R SP anisotropy in the 1998 May 2 event can be explained by the fact that the interplanetary magnetic field (IMF) during the event was in the shape of a giant loop, with its ends starting at the Sun. The bidirectional anisotrop y in the later phase of the event may be caused by the injection of particl es from a vast solar region involving both ends of the looplike structure.