Slow and fast solar wind acceleration near solar maximum

Abstract

2-site measurements of interplanetary scintillation (IPS) provide measurements of solar wind speed in regions of the heliosphere which are otherwise inaccessible. We present results from co-ordinated observations made with the EISCAT and MERLIN facilities during 1999 and 2000, covering heliocentric distances from 7 to 80 solar radii (R) predominantly in the slow solar wind. The 1999 results are compared with optical measurements from LASCO covering 4-30 R. Most slow acceleration appears to take place between 5 and 10 R, but the slow wind continues to accelerate out to 25-35 R. Some of the observations included identifiable fast flow, and in these regions acceleration began lower down and was much more rapid, with 50% of cruising speed reached by 4-5 R and acceleration complete inside 10 R — results which are similar to those from solar minimum.