A STRONG CME-RELATED MAGNETIC CLOUD INTERACTION WITH THE EARTHS MAGNETOSPHERE - ISTP OBSERVATIONS OF RAPID RELATIVISTIC ELECTRON ACCELERATION ON MAY 15, 1997

A geoeffective magnetic cloud impacted the Earth early on 15 May 1997. The cloud exhibited strong initial southward interplanetary magnetic field (B(z)similar to-25 nT), which caused intense substorm activity a nd an intense geomagnetic storm (Dst similar to-170 nT). SAMPEX data s howed that relativistic electrons (E greater than or equal to 1.0 MeV) appeared suddenly deep in the magnetosphere at L=3 to 4. These electr ons were not directly ''injected'' from higher altitudes (i.e., from t he magnetorail), nor did they come from an interplanetary source. The electron increase was preceded (for similar to 2 hrs) by remarkably st rong low-frequency wave activity as seen by CANOPUS ground stations an d by the GOES-8 spacecraft at geostationary orbit. POLAR/CEPPAD measur ements support the result that high-energy electrons suddenly appeared deep in the magnetosphere. Thus, these new multi-point data suggest t hat strong magnetospheric waves can quickly and efficiently accelerate electrons to multi-MeV energies deep in the radiation belts on timesc ales of tens of minutes.