MHD simulations of meso-scale processes in an ICME-like Magnetic Flux Rope

Coronal Mass Ejections (CMEs) are among the main drivers of geomagnetic storms. The intensity of such storms is related to both the amplitude, coherenceand orientation of the magnetic field embedded in the magnetic cloud carried bythe CME, which can be often identified as a Magnetic Flux Rope (MFR). During their propagation in the Heliosphere, MFRs are subjectto meso/small-scale processes such as magnetic reconnection and interaction withturbulent fluctuations. The latter arise from solar wind turbulence,but also include the turbulent sheath region which can form behind theinterplanetary shock driven by the CME.These processes are difficult to capture in global numerical simulations ofCMEs and are possibly responsible for the rather small magneticcorrelation lengths which have been estimated for magnetic clouds, as short as a few tenth of AU. We present a new numerical approach that exploits a lagrangian reference frameto follow the evolution of a MFR via a high-resolution, 2.5D, visco-resistive MHD code implementing spherical expansion (Expanding Box Model).In particular, we simulate the evolution of a low-beta MFR immersed in aturbulent medium and study the resiliency of the magnetic structure as afunction of the amplitude and correlation length of the surrounding turbulence.We present preliminary results using different proxies to estimate the evolutionof MFR coherence and helicity.