Multi-Spacecraft Observations of Interplanetary Shocks Near Earth

Abstract:

Space missions around Earth have been continuously monitoring solar wind and interplanetary magnetic field for many years now. They have detected a large number of interplanetary (IP) shocks. These have been observed with multiple spacecraft at separations ranging from 10³ km to several 10⁵. Comparing observations of IP shocks at different locations in space can provide us with important insights on micro-physical processes that take place near or within the shock transitions. We have compiled a database of about 50 IP shocks detected between 2001 and 2014 with several missions. In the first part of our research we calculated local normals of IP shocks by using different one-spacecraft methods and also the 4-spacecraft method, when possible. In some cases we were able to compare the results of the latter method for different inter-spacecraft separations. This is the first time that comparison of IP shock profiles is also performed systematically on small inter-spacecraft separations of several 100 km (Cluster and Themis observations). Shock normals obtained by using different spacecraft configurations may differ. We find that spacecraft observe different shock profiles even when the their separations are only ~1000 km and the detection times differ by less than a second. The four-spacecraft method is less reliable when the detection times are small, since the changing shock profiles and uncertainties related to timing of the shock arrivals may distort the calculations. We also study regions upstream and downstream of IP shocks - we analyze the properties of suprathermal particles and magnetic perturbations there.