VARIATION OF FRACTIONAL ELECTRON-DENSITY FLUCTUATIONS INSIDE 40-R(O) OBSERVED BY ULYSSES RANGING MEASUREMENTS

The first measurements of fractional electron density fluctuations deltan(e)/n(e), where deltan(e) is rms electron density fluctuation and n(e) is the mean electron density, have been carried out inside 40 R(o) using 1991 Ulysses dual-frequency S- and X-band (13 and 3.6 cm) ranging (time delay) measurements. In the frequency band of approximately 6 x 10(-5) - 8 x 10(-4) Hz (periods of 20 min to 5 hr), deltan(e)/n(e) varies from a high near 20% in the slow wind close to the neutral line to a low of 1% in the fast wind far from the neutral line. For spatial wavenumber K approximately 1.4 x 10(-6) km-1 (period of 5 hr at 250 km/s), deltan(e)/n(e) is essentially independent of heliocentric distance over 0.03-1.0 AU in the slow wind; it is a factor of 30 lower in the fast wind than in the slow wind inside 0.1 AU, but exhibits dramatic growth with heliocentric distance inside 0.3 AU. This latter result reinforces current views of the evolution of MHD turbulence and the association of Alfven waves with high speed streams based on in situ fields and particles measurements beyond 0.3 AU. That regions of enhanced density fluctuations near or above the neutral line coincide with regions of enhanced density confirms previous conclusions that they are the interplanetary manifestation of the heliospheric current sheet and extensions of coronal streamers. While the regions of enhanced density fluctuations lie within those of enhanced density, they have boundaries that are distinctly more abrupt, suggesting the separation of plasma of different nature and origin.