3D velocity distribution functions of heavy ions and kinetic properties of O~(6+) at 1 AU

摘要

The kinetic properties of the solar wind are a result of complex interactions in the solar corona and interplanetary space. So far, observations of Velocity Distribution Functions (VDFs) of solar wind heavy ions have been solely 1D. They are known to exhibit non-thermal features, but because they are 1D projections of the 3D velocity phase space it is difficult to interpret them properly. Based on 3D observations of protons and alpha particles from Helios, we have set up a model for heavy-ion VDFs. In it, the magnetic field vector plays a crucial role by defining the symmetry axis of the VDFs. A thermal anisotropyT_||/T_+ = 1 and a beam drifting along the magnetic field vector at a relative speed of approximately the Alfvdn speed are included. The modeled VDFs are analysed using a virtual detector and then compared with data from the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE). Our observations give evidence for the existence of heavy-ion beams. The projection of these beams can explain observed differential streaming. We present in-situ measurements and derived kinetic properties of 06+ at 1 AU.