Oxygen ion beams at the boundary of velocity dispersed ion structures in the high-latitude magnetosphere under northward interplanetary magnetic field with a large by-component: Interball-tail observations

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Here we discuss two cases of ionospheric ion beam observations by Interball-Tail at altitudes 6–9 R E in the high-latitude magnetosphere under conditions of a strong northward/ duskward directed interplanetary magnetic field (IMF). On November 22, 1997, the magnetosphere was immersed in the magnetic cloud characterized by a large, steady IMF and a tenuous, cold solar wind plasma. Interball-Tail (I-T) was in the prenoon high-latitude region of the south hemisphere, at R∼8 to 5 R E . Plasma data from PROMICS-3 and Corall instruments show that cold ionospheric ions were attached to the boundary of velocity and pitch-angle dispersed (VDIS) hot ion structures. Observed VDIS are similar to that seen typically at mid-altitudes and are known as coming either from the cusp injections or from the plasma sheet boundary layer and the plasma sheet. The other case of observations of ionospheric ion beams at the boundary of VDIS occurred under a somewhat weaker IMF and a more dense solar wind plasma (i.e., not a magnetic cloud event). This time O + beams were observed at the nightside high-latitude magnetosphere, just at the boundary of the plasma sheet. Later along the orbit, when IMF changed direction to a strongly dominating large northward BZ, oxygen ions were seen intermixed with a warm magnetosheath plasma apparently circulating within the dawn cell of the high-latitude NBZ convection system. This kind of data from PROMICS-3 are of a potential value for further coordinated analysis of ISTP events using multipoint observations.