Disparities in Magnetic Cloud Observations Between Two Spacecraft Having Small Radial and Angular Separations Near 1 AU

TL;DR

This study compares magnetic cloud observations from two spacecraft near 1 AU with small separations, revealing significant disparities in CME structure and dynamics, emphasizing the need for multi-point analysis to understand flux rope characteristics.

Contribution

It introduces a novel approach for identifying the magnetic cloud axis's arrival and compares magnetic field parameters at two closely spaced spacecraft, highlighting disparities in CME observations.

Findings

Significant differences in CME substructure arrival times between spacecraft.

MC axis orientation varies slightly between the two spacecraft.

Notable non-coherency and asymmetry in magnetic field parameters across the MC.

Abstract

Studies for inferring the global characteristics of coronal mass ejections (CMEs) from its multipoint local in situ observations have been undertaken earlier, but there are limited studies utilizing measurements from multiple spacecraft with sufficiently small radial and angular separations. In the present study, we investigate a magnetic cloud (MC) region of a CME observed in situ during 2023 September 24-26, at STEREO-A and Wind spacecraft near 1 AU, which had radial and angular separations of 0.03 AU and 3.4 degrees, respectively. We examine the disparities in the estimates of the arrival times of CME substructures, the MC axis, and its orientation between the two spacecraft. We also propose an approach for identifying the MC axis's arrival and have compared it with the arrival of the size/time center to understand the non-isotropic compression of the MC along its angular extent. Using minimum variance analysis (MVA), we note that the orientation of the MC is slightly out-of-ecliptic at Wind but not at STEREO-A. We also compare the magnetic field parameters over the start to end of the MC at both spacecraft and note a significant non-coherency in the MC towards its trailing portion. Our analysis confirms that MC has a stronger rear side compression at STEREO-A than at Wind, with its trailing edge arriving later at Wind. Our study highlights substantial differences in CME characteristics even at mesoscales across the angular extent, and therefore, one needs to analyze several such cases to better understand the flux rope structure.