Shock system of February 2, 1969

The shock system observed in the solar wind by Pioneer 9 and Ogo 5 on February 2, 1969, consisted of the following major discontinuities: a forward slow shock, a forward fast shock, a tangential discontinuity at which the density dropped sharply and the flow direction changed, a tangential discontinuity at which the magnetic field strength jumped to an unusually high value, two closely spaced tangential discontinuities that bracketed a region of even greater field strength and that fronted a region of very cool, very dense, helium-enriched plasma, a reverse fast shock of low Mach number, and a second reverse fast shock of very low Mach number. The event had aspects of both corotating and flare-induced shock systems; it is suggested that the source of the disturbances was a flare occurring at or near an M region. The Ogo 5 search coil magnetometer detected a high level of turbulence throughout the event; a local enhancement of this turbulence at the front of the helium enrichment is believed to have been caused by a magnetic drift wave instability. Data are also presented for two other shock pair systems, both of which had density and flow direction profiles similar to those observed on February 2, 1969.