A STUDY OF DENSITY-FLUCTUATIONS IN THE SOLAR-WIND ACCELERATION REGION

Interplanetary scintillation (IFS) measurements of the density fluctua tions in the fast and slow solar wind were made at 2 GHz and 8 GHz in 1994 at the Kashima. Space Research Center, Communications Research La boratory, Using: the observations which cover the distance range from 5 to 76 solar radii (R-s), we investigate the radial evolution of the dissipation scale length of the density fluctuations, the so-called; i nner scale.'' Our IFS observations reveal that the inner scale shows d ifferent radial profiles between the inside and outside of the acceler ation region, The size of the inner scale outside 25 R-s increases lin early with radial distance, showing: good agreement with previous obse rvations made at r greater than or equal to greater than or equal to 5 0 R-s, The inner scale inside 25 R-s, on the other hand, deviates from the linear relation, We simulate the radial variation of the inner sc ale using-a solar wind acceleration model and then compare the results to that of the observed inner scale, We find that. in the low-speed s olar wind, the radial profile of the computed inner scale is in good a greement with that of the observed inner scale and that the salar wind acceleration causes the deviation of the inner scale from a linear re lation, However, in the high-speed wind, we cannot reproduce the radia l profile of the observed inner scale with the acceleration model, eve n though the line-of-sight integration effect on IFS measurements is t aken into account, We propose that this disagreement is due to the den sity and magnetic field fluctuations not being correlated in the high- speed solar wind, as shown at greater heliocentric distances by Hellos measurements.