SOLAR-WIND VELOCITY DISTRIBUTION ON THE HELIOSPHERIC CURRENT SHEET DURING CARRINGTON ROTATIONS-1787-1795

The solar wind velocity distribution in the heliosphere is best repres ented using a v-map, where velocity contours are plotted in heliograph ic latitude-longitude coordinates. It has already been established tha t low-seed regions of the solar wind on the source surface correspond to the maximum bright regions of the K-corona and the neutral line of the coronal magnetic field. In this analysis, v-maps on the source sur face for Carrington rotations (CRs) 1787-1795, during 1987, have been prepared using the interplanetary scintillation measurements at Resear ch Institute of Atmospherics (RIA), Nagoya Univ., Japan. These v-maps were then used to study the time evolution of the low-speed (less than or equal to 450 kms s(-1)) belt of the solar wind and to deduce the d istribution of solar wind velocity on the heliospheric current sheet. The low-speed belt of the solar wind on the source surface was found t o change from one CR to the next, implying a time evolution. Instead o f a slow and systematic evolution, the pattern of distribution of sola r wind changed dramatically at one particular solar rotation (CR 1792) and the distributions for the succeeding rotations were similar to th is pattern. The low-speed region, in most cases, was found to be close to the solar equator and almost parallel to it. However, during some solar rotations, they were found to be organized in certain longitudes , leaving regions with longitudinal width greater than 30 degrees free of low-speed solar wind, i.e. these regions were occupied by solar wi nd with velocities greater than 450 km s(-1). It is also noted from th is study that the low-speed belt, in general, followed the neutral lin e of the coronal magnetic field, except in certain cases. The solar wi nd velocity on the heliospheric current sheet (HCS) varied in the rang e 300-585 km s(-1) during the period of study, and the pattern of velo city distribution varied from rotation to rotation.