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.