Abstract. The present paper focuses on the altitude dependence of oxygen ion conics in the dayside cusp/cleft region. Here, combining oxygen data from the Akebono, Interball-2 and Cluster satellites allows, for the first time, one to follow the global development of energetic (up to ∼10 keV) ion outflow over a continuous and broad altitude range up to about 5.5 Earth radii (R E ). According to earlier statistical studies, the results are consistent with a height-integrated energization of ions at altitudes up to 3.5 R E . Higher up, the results inferred from Cluster observations put forward evidence of a saturation of both a transverse energization rate and ion gyroradii. We suggest that such results may be interpreted as finite perpendicular wavelength effects (a few tens of km) in the wave-particle interactions. To substantiate the suggestion, we carry out two-dimensional, Monte Carlo simulations of ion conic production that incorporate such effects and limited residence times due to the finite latitudinal extent of the heating region.

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Abstract.The results of a statistical study of oxygen ion outflow using Cluster data obtained at high altitude above the polar cap is reported. Moment data for both hydrogen ions (H + ) and oxygen ions (O + ) from 3 years (2001)(2002)(2003) of spring orbits (January to May) have been used. The altitudes covered were mainly in the range 5-12 R E geocentric distance. It was found that O + is significantly transversely energized at high altitudes, indicated both by high perpendicular temperatures for low magnetic field values as well as by a tendency towards higher perpendicular than parallel temperature distributions for the highest observed temperatures. The O + parallel bulk velocity increases with altitude in particular for the lowest observed altitude intervals. O + parallel bulk velocities in excess of 60 km s −1 were found mainly at higher altitudes corresponding to magnetic field strengths of less than 100 nT. For the highest observed parallel bulk velocities of O + the thermal velocity exceeds the bulk velocity, indicating that the beam-like character of the distribution is lost. The parallel bulk velocity of the H + and O + was found to typically be close to the same throughout the observation interval when the H + bulk velocity was calculated for all pitch-angles. When the H + bulk velocity was calculated for upward moving particles only the H + parallel bulk velocity was typically higher than that of O + . The parallel bulk velocity is close to the same for a wide range of Correspondence to: H. Nilsson (hans.nilsson@irf.se) relative abundance of the two ion species, including when the O + ions dominates. The thermal velocity of O + was always well below that of H + . Thus perpendicular energization that is more effective for O + takes place, but this is not enough to explain the close to similar parallel velocities. Further parallel acceleration must occur. The results presented constrain the models of perpendicular heating and parallel acceleration. In particular centrifugal acceleration of the outflowing ions, which may provide the same parallel velocity increase to the two ion species and a two-stream interaction are discussed in the context of the measurements.

Abstract. The transport patterns of non-thermal H + and O + field-aligned flows from the dayside cusp/cleft, associated with transverse heating by means of wave-particle interactions and in combination with the poleward motion due to the magnetospheric convection are investigated. This has been accomplished by developing a steady-state, twodimensional, trajectory-based code. The ion heating is modelled by means of a Monte Carlo technique, via the process of ion cyclotron resonance (ICR), with the electromagnetic left-hand circular polarized component of a broad-band, extremely low-frequency (BBELF) turbulence. The altitude dependence of ICR heating from 1000 km to 3 Earth radii (R E ) is modelled by a power law spectrum, with an index α, and a parameter w 0 that is proportional to the spectral density at a referenced gyrofrequency. Because of the finite latitudinal extent of the cusp/cleft, the incorporation of the horizontal convection drift leads to a maximum residence time t D of the ions when being energized. A large set of simulations has been computed so as to study the transport patterns of the H + and O + bulk parameters as a function of t D , α, and w 0 . Residence time effects are significant in O + density patterns while negligible for H + . When comparing the results with analytical one-dimensional theories (Chang et al., 1986;Crew et al., 1990), we find that mean ion energies and pitch angles at the poleward edge of the heating region are slightly influenced by t D and may be used as a probe of ICR parameters (α, w 0 ). Conversely, poleward of the heating region, upward velocity and mean energy dispersive patterns depend mainly on t D (e.g. the magnitude of the convection drift) with latitudinal profiles varying versus t D . In short, the main conclusion of the paper is that any triplet (t D , α, w 0 ) leads to a unique transport-pattern feature of ion flows associated with a cusp/cleft ionospheric source. In a companion paper, by using high-altitude (1.5-3 R E ) ion observations as constraints, the results from the parametric study are used to determine the altitude dependence of transverse ion heatingCorrespondence to: M. Bouhram (bouhram@mpe.mpg.de) during a significant number of passes of the Interball-2 satellite.