Energy input to O VI ions and protons in the fast solar wind

Details Energy input to O VI ions and protons in the fast solar wind Energy input to O VI ions and protons in the fast solar wind

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002esasp.508..493z&link_type=abstract

In: Proceedings of the SOHO 11 Symposium on From Solar Min to Max: Half a Solar Cycle with SOHO, 11-15 March 2002, Davos, Switze

Physics

Sun: Corona, Sun: Uv Radiation, Solar Wind

Scientific paper

Observations with UVCS of a polar coronal hole, acquired during August 1996, have been analysed with the purpose of deriving the radial and latitudinal outflow speed profiles of O VI ions and protons in the altitude range between 1.4 and 2.6 Rsolar, and latitudes between 40° and 90°. We used the results obtained along the direction of the North pole to estimate the energy input to O VI and protons in the extended solar corona. The O VI and proton outflow speeds have been derived from a Doppler dimming analysis of the λλ1031.9, 1037.6 O VI doublet and H I Lyα λ1215.6 lines. The coronal hole morphology has been modelled with a simple magnetic field geometry, in order to derive the expansion factor of the magnetic field lines. The O VI and H I Lyα line intensities and the mass flux at 1 A.U. have been used as constraints for identifying the physical conditions of the plasma where lines originate. The free parameters that allowed us to comply with the requirement of a constant mass flux throughout the region we examine, are the magnetic field geometry, and the O VI parallel kinetic temperature, for which we have no direct information from observations. It turns out that the temperature anisotropy increases with altitude, indicating an increasing asymmetry of the ion distribution about the magnetic field lines, possibly related to the heavy ions heating mechanism. Our results show that the oxygen ions flow at speed of ~350 km s-1, at the highest level we consider, 2.6 Rsolar, in polar regions. However, as the latitude decreases, the outflow speed tends to decrease, and, for latitudes lower than 60° and altitudes greater than 2 Rsolar, keeps below ~300 km s-1. From the analysis of polar data we found that the O VI heating rate is larger than the proton heating rate, and it increases with distance.

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