A correlative study of ssc's, interplanetary shocks, and solar activity

We have examined 93 ssc's during the 4‐year period from 1968 to 1971 at and near the peak of the solar activity cycle. Of the 93 ssc's, 81 could be associated with solar activity such as solar flares and type 2 and type 4 radio bursts. The mean propagation speeds of these flare‐associated events ranged from 400 to 1000 km/s, the average speed being 600–700 km/s. Disturbances associated with 48 of the ssc's have been studied in detail by using the corresponding interplanetary (IP) magnetic field and plasma data when they were available. We found that 41 of the 48 disturbances corresponded to IP shock waves, and the remaining 7 events were tangential discontinuities. Thirty percent of the IP shocks had thick structure (i.e., the magnetic field jump across the shock occurred over a distance much greater than 50 proton Larmor radii). Also given is a statistical study of the gross geometry of a ‘typical’ or average shock surface based on multiple spacecraft sightings and their relative orientation with respect to the solar flare and/or solar activity. By considering the orientations of 22 well‐determined shock normals in relation to the positions of the parent flares on the solar disk, a method that is a modification of one given by Taylor (1969), it is suggested that a typical shock front propagating out from the sun at 1 AU has a radius of curvature of the order of 1 AU. Also given are some general properties of oblique IP. flare shocks.