Multi-spacecraft observations of ICMEs propagating from 1 AU to 1.5 AU
Abstract
The Radiation Assessment Detector (RAD) instrument on the Curiosity rover (Mars Science Laboratory mission) has been measuring galactic cosmic rays on the surface of Mars since its landing 4 years ago. Using this data, we can detect Forbush decreases caused by ICMEs passing Mars. To gain a better understanding of the propagation of individual ICMEs from 1 AU (Earth orbit) to 1.5 AU (Mars orbit), we investigate events that took place close to the oppositions of Earth (as well as STEREO A and B) and Mars, i.e., when they were nearly in a straight line on the same side of the Sun in the ecliptic plane. Such lineups allow us to estimate the ICMEs’ transit time by estimating the delay time of the corresponding Forbush decreases between data from Earth’s orbit (such as neutron monitors on Earth and HEP on both STEREOs) and Mars (RAD). Based on the radial distance between the two measurement locations, the ambient solar wind speeds and the properties of these ICMEs determined in previous studies, we investigate the evolution of the ICME’s speed and/or shape during its propagation in the interplanetary medium beyond Earth orbit.
