Disparities in Magnetic Cloud Observations between Two Spacecraft Having Small Radial and Angular Separations near 1 au

Abstract Studies for inferring the global characteristics of coronal mass ejections (CMEs) from multipoint local in situ observations have been undertaken previously, but limited studies have utilized 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 by the STEREO-A and Wind spacecraft near 1 au, which had radial and angular separations of 0.03 au and 3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 4, 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 center and time center to understand the nonisotropic compression of the MC along its angular extent. Using minimum variance analysis, we note that the orientation of the MC is slightly out of the ecliptic at Wind but not at STEREO-A. We also compare the magnetic field parameters from the start to the end of the MC at both spacecraft and note a significant noncoherency in the MC toward its trailing portion. Our analysis confirms that the MC has a stronger compression at the rear portion 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.