Visualizing the Magnetic Structure in Interplanetary Coronal Mass Ejections with ATHARV

Interplanetary coronal mass ejections (ICMEs) are major drivers of space weather, and their geoeffectiveness is strongly governed by the structure and orientation of their internal magnetic field. However, in-situ observations provide only one-dimensional sampling of magnetic-field properties along the spacecraft trajectory, limiting direct inference of the three-dimensional ICME magnetic structure. We introduce the Analysis Tool for Heliospheric Arrangement of Remapped Vectors (ATHARV), which remaps in-situ time-series data into spatial coordinates while accounting for ICME expansion and spacecraft motion. The framework assumes self-similar expansion with different expansion rates along three orthogonal directions, while more general cases use measured velocities as proxies for plasma motion. ATHARV also incorporates complementary diagnostics, including hodograms and magnetic-field orientation angles, to assess magnetic coherence and field rotation within ICMEs. We demonstrate the application of ATHARV using multipoint in-situ observations of an ICME detected near 1 au by STEREO-A and Wind on 2023 April 23–24. The reconstructed sheath region exhibits variable and disordered magnetic fields, whereas the magnetic ejecta (ME) shows a coherent rotation consistent with a south–west–north flux-rope configuration with right-handed helicity at both spacecraft. However, differences in the magnetic-field magnitude profiles, rotation signatures, and inferred ME sizes between the two spacecraft suggest mesoscale inhomogeneity within the ICME magnetic configuration, possibly associated with a writhed or distorted flux-rope geometry. This event highlights the limitations of interpreting the magnetic configuration of ICMEs from single-point measurements alone and demonstrates the importance of multipoint observations for investigating their three-dimensional structure and evolution. Overall, ATHARV provides a consistent framework for interpreting in-situ ICME observations and investigating their spatial structure and evolution. ATHARV is available online for the heliophysics community.