Dual observations of interplanetary shocks associated with stream interaction regions

Abstract

We investigate the characteristics of 9 interplanetary shocks associated with stream interaction regions observed by both STEREO-A and STEREO-B spacecraft during the years 2007-2008. Interplanetary shocks modify the plasma both upstream and downstream of the front shock. As they propagate, interplanetary shocks encounter solar wind with different characteristics (density, velocity) and different orientations of ambient magnetic field relative to the shock normal. Thus, it is interesting to compare dual observations of stream interaction shocks at the locations of the two spacecraft to determine the role of these parameters in controlling both the structure at the shock but also in the regions upstream and downstream from the shock. The range of shock normal angle (θBn) values observed by spacecraft covered the range from ∼20° to ∼81°. The largest difference in θBn for the same shock observed at two different longitudinal locations was ∼39°. The shock magnetosonic Mach numbers covered the range of ∼1.1 to ∼2.2, having a largest change for the same shock of ∼0.9. The jump in the field magnitude, i.e., the ratio of downstream magnetic field intensity to upstream magnetic field intensity (B d/Bu), ranged from ∼1.1 to ∼2.25. The largest difference in the jump in field magnitude for the same shock at two different locations was ∼0.72. These variations with longitude of shock properties observed with the STEREO dual mission show the non-homogeneous character of the plasma in the heliosphere, and they need to be taken into account to understand in detail how these shocks modify the solar wind, and affect the acceleration processes of energetic particles in the solar wind. Copyright 2011 by the American Geophysical Union.