Deformation of ICMEs/MCs along their path

Interplanetary coronal mass ejections (ICMEs) and their subset, magnetic clouds (MCs), are important manifestations of solar activity which have substantial impact on the geomagnetic field. We re-analyze events already identified in Wind and Voyager 2 data and estimate changes of their geometry along the path from the Sun. The analysis is based on the thickness of the sheath between a shock and a particular ICME or MC which is proportional to the apparent curvature radius of ICMEs/MCs. We have found that this apparent radius of curvature increases with the Mach number and this effect is attributed to the larger deformation of the fast ICME/MC. Further, the relative sheath thickness that is proportional to the flux rope oblateness decreases with the magnetic field intensity inside the ICME/MC and increases with the heliospheric distance.

► We re-analyze ICME and MC events and estimate changes of their geometry along the path.
► We use the thickness of the sheath between a shock and a ICME/MC to determine their curvature radius.
► The sheath thickness increases with the Mach number.
► The sheath thickness decreases with the magnetic field intensity inside the ICME/MC.
► If the magnetic field inside the ICME/MC is much stronger than that in the ambient solar wind, the ICME/MC cross-section is closer to circular.