MAGNETOSHEATH-IONOSPHERIC PLASMA INTERACTIONS IN THE CUSP CLEFT .1. OBSERVATIONS OF MODULATED INJECTIONS AND UPWELLING ION FLUXES

Insitu observations of the cusp/cleft are important as they allow a di rect investigation of coupling solar wind energy to the ionosphere, pl us they provide an opportunity for the remote sensing of the magnetopa use. High time resolution observations from DE 1 are used to investiga te these processes. It is shown that in the spacecraft frame the injec tion in modulated or pulsating with a period of approximately 18 - 30 s with the injection duration possibly being as short as 6 s. This mod ulation indicates that there may be fast time scale and/or short scale length processes modulating the injection of the magnetosheath plasma across the magnetopause. In addition, the pulsating injection is seen to modulate the outflow of upwelling ionospheric ions to the magnetos phere. These upwelling ions are seen prior to the magnetosheath ion in jection and therefore are not directly created by the injection. Durin g the injection itself, the intensity of the upwelling ions is seen to dramatically decrease but their average energy increases. At end of t he magnetosheath injections, the intensity of the upwelling ion flux i s seen to increase to levels comparable to levels prior to the magneto sheath injection. On two occasions during the encounter, the particle fluxes we sufficiently high that enhanced downward flows of perpendicu larly heated ions, of presumably ionospheric origin, are observed in a ssociation with a reduction in the intensity of the upwelling ions. Th ese observations are probably the first detection of. downward conics and suggest that there is momentum transfer between the magnetosheath and ionospheric ions. This momentum transfer eventually leads to an en hanced outflow of heated ionospheric plasma where their energy has bee n raised from a few tens of eV to a few hundred eV.