SPATIAL EVOLUTION OF THE MAGNETIC-FIELD SPECTRAL EXPONENT IN THE SOLAR-WIND - HELIOS AND ULYSSES COMPARISON

The spatial evolution of the spectral exponent of magnetic field fluct uations in the solar wind is investigated by a comparison of spectra a nd length functions obtained from Hellos for in-ecliptic and from Ulys ses for high-latitude observations. A similar radial evolution trend i s found in both data sets for the B-z component of the magnetic field, which is least affected by compressive interactions. Yet the fluctuat ions seem to evolve more slowly in the polar flows as compared with th e Alfvenic fluctuations found by the Hellos experiments in coronal-hol e-related flows near the Sun in the ecliptic plane.