Regensburg 2007 – wissenschaftliches Programm
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EP: Fachverband Extraterrestrische Physik
EP 10: Poster
EP 10.17: Poster
Mittwoch, 28. März 2007, 18:00–20:00, H46
Diffusion plateaus and temperature anisotropies of proton velocity distributions in fast solar wind — •Eckart Marsch1, Michael Heuer1, Liang Zhao2, and Chuanyi Tu2 — 1Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau — 2Department of Geophysics, Peking University, Beijing, China
In a collisionless plasma, such as the fast solar wind, wave-particle interactions play the decisive role in determining the shape of particle velocity distribution functions (VDFs). In this talk we provide observational evidence for resonant interaction of ion-cyclotron-Alfven waves with fast solar-wind protons. According to quasi-linear theory, the protons thereby diffuse in velocity space, a process leading to the formation of plateaus in their VDFs. We investigate a large number of data from several fast solar wind streams between 0.3 and 1 AU. The measured proton VDFs are used, and the plasma dispersion relation for parallel propagating cyclotron waves is solved numerically. Thus the details of the proton VDFs are well represented and reflected in the dispersion relation, which makes our analysis as self-consistent as possible. We also analyse the core temperature anisotropy of the protons by deriving the temperature in the directions perpendicular and parallel to the magnetic field, as well as the core parallel plasma beta. Statistical results on these parameters are presented in histograms. The data are compared with known theoretical instability thresholds. The core protons are found to come with increasing radial distance closer to the fire-hose instability threshold.