Electron properties of high-speed solar wind from polar coronal holes obtained by Ulysses thermal noise spectroscopy: not so dense, not so hot

International audienceWe present radio observations of Ulysses' third fast latitude scan near the 2007 solar activity minimum of cycle 23. We deduce in situ measurements of the electron density and temperature using the method of quasi-thermal noise spectroscopy. We study the large-scale properties of the fast solar wind coming from polar coronal holes and compare our results to those obtained during Ulysses' first fast scan in 1994-1995 near the minimum of cycle 22. The fast solar wind in both hemispheres is less dense and cooler by about 19% and 13% respectively, as compared to the last solar minimum