Interplanetary Coronal Mass Ejections from MAVEN Orbital Observations at Mars

Abstract

The measurements from the Mars Atmosphere and Volatile EvolutioN spacecraft, in orbit around Mars, are utilized to investigate interplanetary coronal mass ejections (ICMEs) near 1.52 au. We identify 24 ICMEs from 2014 December 6 to 2019 February 21. The ICME list is used to examine the statistical properties of ICMEs. On average, the magnetic field strength of 5.99 nT in ICMEs is higher than that of 5.38 nT for stream interaction regions (SIRs). The density of 5.27 cm −3 for ICMEs is quite comparable to that of 5.17 cm −3 for SIRs, the velocity of 394.7 km s −1 for ICMEs is slightly lower than that of 432.8 km s −1 for SIRs, and the corresponding dynamic pressure of 1.34 nPa for ICMEs is smaller than that of 1.50 nPa for SIRs. Using existing databases of ICMEs at 1 au for the same time period, we compare ICME average properties at 1.52 au with those at 1 au. The averages of the characteristic quantities decrease by a factor of 1.1–1.7 from 1 to 1.52 au. In addition, we analyze an unusual space weather event associated with the ICME on 2015 March 9–10, and propose that the extremely strong dynamic pressure with a maximum of ∼18 nPa on March 8 is caused by the combined effects of the enhanced density inside a heliospheric plasma sheet (HPS), the compression of the HPS by the forward shock, and the high velocity of the sheath ahead of the ICME.