Resolving the Ambiguity of a Magnetic Cloud's Orientation Caused by Minimum Variance Analysis Comparing it with a Force-Free Model

Autor(es)

Rosa Oliveira, Rosemeire Aparecida ^[1] ; da Silva Oliveira, Marcos William ^[2] ; Ojeda-Gonzalez, Arian ^[1] ; Pillat, Valdir Gil ^[1] ; Echer, Ezequiel ^[3] ; Nieves-Chinchilla, Teresa ^[4]

Afiliação do(s) autor(es)

^[1] Univ Vale Paraiba UNIVAP, Phys & Astron Lab, Sao Jose Dos Campos, SP - Brazil

^[2] Fed Inst Educ Sci & Technol Sao Paulo IFSP, Sao Jose Dos Campos, SP - Brazil

^[3] Natl Inst Space Res INPE, Heliophys Planetary Sci & Aeron Dept, Sao Jose Dos Campos, SP - Brazil

^[4] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 - USA

• Tipo de documento: Artigo Científico
• Fonte: SOLAR PHYSICS; v. 296, n. 12 DEC 2021.
• Citações Web of Science: 0

Resumo

This study aims to incorporate an algebraic and computational method for calculating the angles of the magnetic clouds' (MC) axis from the minimum variance analysis (MVA) and correcting them compared to a simulated model from the linear, force-free approximation. Consequently, it determines the type of flux-rope consistently and automatically. In general, MCs measured in situ at 1 Astronomical Unit (AU) may be approximated to have a cylindrical geometry, and the internal magnetic-field topology is traditionally described by a force-free equilibrium flux-rope model. Based on the B-z-rotation, the flux-rope configuration can be classified in eight groups. This classification is obtained from the angle of rotation of the magnetic-field vector and inclination of the flux-rope axis (phi, theta) in relation to the plane of the Ecliptic. The MVA is applied to interplanetary magnetic-field (IMF) observations to obtain the direction of the cylinder axis. However, MVA estimates may have an ambiguity of 180 degrees in this direction. This is directly affected by the eigenvector signal since eigenvalues in MVA are always positive. To apply the methodology, a sample of 50 MC events measured by the Advance Composition Explorer (ACE) spacecraft was investigated in the period from 1998 to 2003. 83.72% of the analysed events achieved a satisfactory match between the maximum- and minimum-variance planes (from MVA) with the model (force-free) and (phi, theta) angles consistent with the MC geometry. Moreover, automatic classification of the MC or flux-rope tube type related to the MC-axis was consistent for 100% of the events studied. This processing is organized in a computational tool described in this publication. We discuss the results and implications of our analysis of six magnetic cloud events in 2018 during the solar minimum.

• Processo FAPESP: 18/21657-1 - Estudo da variabilidade da atividade auroral em rádio da magnetosfera de Júpiter
• Beneficiário: Ezequiel Echer
• Modalidade de apoio: Auxílio à Pesquisa - Regular