J L Roeder and J F Fennell (Aerospace Corporation, Los Angeles, CA 90009; 310-336-7081; e-mail: jim_roeder@qmail2.aero.org) M Grande (Rutherford Appleton National Laboratory, United Kingdom) S Livi (Max Planck Institute for Aeronomy, Germany) R Sheldon (Department of Astronomy and Space Physics, Boston University, Boston, MA 02215)

Interplanetary magnetic cloud events appear to have a wide range of ability to affect the magnetospheric energetic particle populations. This "effectiveness" or lack thereof, shows up in both the electron and ion components of the radiation belts. The ring current ions are intensified and energized by the geomagnetic storm response to the cloud. The ion composition of the ring current may also change due to source variations in the solar wind and ionosphere. The three largest magnetic cloud events during the first year of the GGS Polar mission are compared as to their effectiveness to change the intensity and composition of the ring current ion populations . Data from both the CEPPAD energetic ion sensors and the CAMMICE MICS ion composition instrument on Polar are presented to quantify the ring current response to each event. For example, the May 29, 1996 event was observed to have a relatively small effect on the ring current, perhaps due to the predominantly northward interplanetary magnetic field. In contrast, the cloud that arrived on January 10, 1997 resulted in ring current ion flux enhancements approximately one order of magnitude larger. These events are compared with those observed by the CRRES spacecraft using similar instru-mentation during solar maximum.