OBSERVATION OF THE 40 KEV FIELD-ALIGNED ION-BEAMS

Recent observations by CEPPAD/IPS from the new perspective of the POLA R orbit reveal a close association of field-aligned ionospheric beams with convecting plasmasheet ''nose'' ions. April 15, 1996 was marked b y a large southward B-z accompanying a fast solar wind shock. This eve nt triggered a strong cross-tail convection electric field that pushed plasmasheet ions deep into the magnetosphere. When the POLAR spacecra ft passed through the inner magnetosphere, it observed both an unusual ly energetic plasmasheet nose ion injection at similar to 90 keV, as w ell as a peculiar field-aligned beam at similar to 40 keV. These beams appear to be enriched in oxygen ions (as inferred from other instrume nts), which would place their origin in the ionosphere. Both populatio ns existed from L=7-3, for a duration of at least 2 hours. We speculat e that the nose ions create a parallel electric field that is responsi ble for the extended ionospheric beam signature.