Solar wind dynamic pressure enhancements in upstream region near Mars

Abstract

While it has been recognized that solar wind dynamic pressure (Pdy) enhancements have dramatic impacts on the Martian system, their characteristics have not been systematically analyzed due to the lack of upstream plasma observations. Simultaneous measurements of plasma and magnetic field made by MAVEN provide such an opportunity. In this paper, we analyze the distribution of solar wind dynamic pressure and the association of Pdy enhancements with various solar wind structures using MAVEN data from 2014 December 6 to 2021 August 14, covering the declining phase of solar cycle 24 to the ascending phase of solar cycle 25. The results suggest that Pdy above 2 nPa (4 nPa) occurs about 5.82% (0.59%) of the time. Stream interaction region (SIR) encounters, together with heliosphere plasma sheet (HPS) within SIR encounters, are responsible for 36.6% and 31.4% of the dynamic pressure enhancement events with Pdy> 2 nPa and with durations > 10 min, respectively. It is also found that HPSs tend to occur in the leading portion of SIRs, causing an additional deceleration of the slow stream and an additional enhanced local compression in the interaction region. As a result, the Pdy and the magnetic field strength reveal a faster and greater increase and recovery during the SIR with HPS events than they do during the SIR without HPS events. In addition, we compare these results with similar analyses based on the measurements from the Wind spacecraft at 1 AU.