Pioneer 9 and Ogo 5 observations of an interplanetary multiple shock ensemble on February 2, 1969

Abstract

A multiple shock system was observed upstream (0.13 AU) of the earth by Pioneer 9 on February 2, 1969. The same system was observed at earth by Ogo 5 and was reported separately in the literature. This paper compares the two sets of observations in still further detail. Both magnetic field and plasma data are used in a least squares best fit method to compute the characteristics of the fast forward shock wave (Pioneer 9 only) and two fast reverse shock waves. Nearly all major features (shocks, piston, and tangential discontinuity) retained their characteristics during the transit of the shock ensemble from Pioneer 9 to Ogo 5. The genesis of the ensemble is believed to be due to a complex stream-stream interaction. A substantial density increase (including a large rise of alpha/proton abundance) at Ogo 5, but unobserved at Pioneer 9, is explained by a sudden meridional shift to a flow from below the ecliptic plane while the streams were en route to earth. Thus this study, which is the first to examine in such detail observations of a multiple shock ensemble on a scale of 0.13 AU, demonstrates a spatial and temporal plasma inhomogeneity which is superimposed on the persistent major features.