The bow shock velocity from two-point measurements in frame of the interball project Original Research Article

The bow shock is a highly dynamic boundary controlled by steady and transient variations in solar wind parameters. It has been found that both shape and position of this boundary are determined mainly by the dynamic pressure and by the upstream Mach number of the incoming solar wind. Intervals of multiple bow shock crossings, often lasting over intervals from minutes to hours, are currently interpreted in terms of bow shock motions with respect to the observing spacecraft. In the present paper, we examine the bow shock velocity based on several series as well as several single bow shock crossings observed by two closely separated spacecraft (MAGION-4/INTERBALL-1). Our estimations of the bow shock velocity typically ranges from several tens of kilometers per second to approx. 120 km/s. These results correspond to those previously published for quasiperpendicular shocks but our set contains both quasiparallel and quasiperpendicular shocks. An analysis shows that about 80% of crossings can be explained by radial expansion/compression of the bow shock surface. The timing of the rest of events requires another mechanisms for explanation.