Interplanetary shock waves and comet brightness fluctuations during June-August 1972

Abstract

A series of anomalous events associated with solar activity occurred in interplanetary space in June and August 1972. These events include non-Io-associated decametric emission from Jupiter; brightness variations of the periodic comets Schwassmann-Wachmann 1 and Giacobini-Zinner; interplanetary shock waves detected by Pioneer 9 and 10, Heos 2, and Prognoz and Prognoz 2; interplanetary scintillations; and sudden commencements of geomagnetic storms. Trajectories and deceleration characteristics for the shock waves are estimated primarily from observations using solar radio, in situ, and geomagnetic data. Generally, the trajectories indicate a piston-driven character to about 0.3–0.4 AU, after which the shocks decay to a blastlike motion with a shock velocity variation approximately inversely proportional to the heliocentric radius. Most of the shock waves apparently decayed into magnetoacoustic waves between 2 and 4 AU. In our opinion this decay explains the fact that no anomalous events occurred at either Jupiter or P/Schwassmann-Wachmann I at 5.2 and 5.6 AU, respectively, during August 1972.