[1] During storm times, O + can dominate both the pressure and the density in the plasma sheet. Because of the contribution from ion outflow, the plasma sheet is already oxygen-rich prior to substorm onset. At substorm onset the fraction of O + contributing to the pressure and density increases. In the O + dominated thin current sheet the O + ions are observed to stream from dawn to dusk across the tail, as predicted for nonadiabatic ions by Speiser (1965). We calculate the current contribution from these ions and find that they carry about 5-10% of the cross-tail current. During a nonstormtime substorm the general behavior of the O + is the same. However, because there is less O + present, the O + never dominates over H + , and the contribution to the cross-tail current is even less. , et al. (2005), Contribution of nonadiabatic ions to the cross-tail current in an O + dominated thin current sheet,

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Abstract. This paper presents in-situ observational evidence from the Cluster Ion Spectrometer (CIS) on Cluster of injected solar wind "plasma clouds" protruding into the dayside high-latitude magnetopause. The plasma clouds, presumably injected by a transient process through the dayside magnetopause, show characteristics implying a genera-

Abstract. This paper presents the first observations with Cluster of a very dense population of thermal ionospheric ions (H + , He + , O + ) locally "accelerated" perpendicularly to the local magnetic field in a region adjacent to the magnetopause and on its magnetospheric side. The observation periods follow a long period of very weak magnetic activity. Recurrent motions of the magnetopause are, in the presented cases, unexpectedly associated with the appearance inside closed field lines of recurrent energy structures of ionospheric ions with energies in the 5 eV to ∼ 1000 eV range. The heaviest ions were detected with the highest energies. Here, the ion behaviour is interpreted as resulting from local electric field enhancements/decreases which adiabatically enhance/lower the bulk energy of a local dense thermal ion population. This drift effect, which is directly linked to magnetopause motions caused by pressure changes, allows for the thermal ions to overcome the satellite potential and be detected by the suprathermal CIS Cluster experiment. When fast flowing, i.e. when detectable, the density (∼ 1 cm −3 ) of these ions from a terrestrial origin is (in the cases presented here) largely higher than the local density of ions from magnetospheric/plasma sheet origin which poses again the question of the relative importance of solar and ionospheric sources for the magnetospheric plasma even during very quiet magnetic conditions.

The conditions necessary for the production of gyrophase bunched ions at the bow shock are developed. The conditions are applied to the reflection mechanism presented by Paschmann et al. (1980), showing that when in their model a portion of the incident parallel velocity is converted into reflected perpendicular velocity, the reflected particles are gyrophase bunched. The growth of velocity space structure in the gyrophase bunched distribution through gyrophase mixing is also explored. The structure is found to be similar to that reported in diffuse and dispersed ion events. This together with the close correlation of the observation of gyrophase bunched ions with diffuse and dispersed ions has led us to speculate that these two populations may be closely related.