Solar cycle variation of interplanetary shocks, coronal mass ejections, and stream interactions observed at 0.7 AU
A survey of the Pioneer Venus Orbiter (PVO) magnetometer and plasma data from 1979-1988, shows that the occurrence frequency of interplanetary shocks, coronal mass ejections (CMEs) and stream interactions observed at 0.7 AU exhibits a solar cycle variation. As previously found at 1 AU, the observed number of both interplanetary shocks and CMEs peaks during solar maximum (~16 and ~27 per year, respectively) and reaches a low during solar minimum (~0 and ~7 per year, respectively), in phase with the variation in smoothed sunspot number. The number of stream interactions observed varies in the opposite manner, having a minimum during solar maximum (~15 per year) and a maximum during solar minimum (~34 per year). The percentage of CMEs and stream interactions producing interplanetary shocks also varies during the solar-cycle and exhibits interesting behavior during the declining phase. While the number of CMEs observed during this phase is decreasing, the percentage of CMEs producing interplanetary shocks reaches a maximum. Also, while the number of stream interactions observed is increasing, but has not reached maximum during the declining phase, the percentage of stream interactions producing interplanetary shocks is at a maximum.