Dual Observations of Interplanetary Shocks Associated with Stream Interaction Regions

We investigate the characteristics of 10 interplanetary (IP) shocks associated with stream interaction regions (SIRs) observed by both STEREO-A and STEREO-B spacecraft during the years 2007-2008. IP shocks are responsible for several processes that modify the plasma ahead and behind them. As they propagate, IP shocks encounter solar wind with different characteristics (density, velocity) and different orientations of ambient magnetic field. Thus, it is interesting to compare dual observations of SIRs to identify changes in shock structure, strength, and orientation from two different spacecraft. We find that STEREO-A observed shocks with theta_bn ranging in the interval ~45 to ~80 degrees. In contrast, at STEREO-B the same shock fronts have a range of theta_bn between ~19 and ~80 degrees. The shock Mach numbers were similar in both observations, with values in the interval ~1.1 to ~2.2. The magnetic field jump values were also similar in the shocks observed by both spacecraft (~1.1 to ~2.25). Plasma beta values were larger in the shocks observed by STEREO-B than those observed by STEREO-A. The difference observed in shock parameters translate into different shock structure at the two spacecraft locations, and different extensions on the associated foreshocks in the upstream region. We study wave characteristics upstream and downstream of shocks in order to relate Mach number and theta_bn values with the kind of waves generated in these regions. We also determine the extension of the foreshock region.