Characterisation of suprathermal electron pitch-angle distributions: Bidirectional and isotropic periods in solar wind
Authors
Carcaboso Morales, Fernando; Gómez Herrero, Raúl; Espinosa Lara, Francisco; Hidalgo Moreno, Miguel Ángel; Cernuda Cangas, Ignacio Manuel; [et al.]Identifiers
Permanent link (URI): http://hdl.handle.net/10017/58827DOI: 10.1051/0004-6361/201936601
ISSN: 0004-6361
Publisher
The European Southern Observatory (ESO)
Date
2020-03-10Funders
Agencia Estatal de Investigación
Bibliographic citation
Carcaboso Morales, F., Gómez Herrero, R., Espinosa Lara, F., Hidalgo Moreno, M.A., Cernuda Cangas, I.M. & Rodríguez-Pacheco Martín, J. 2020, “Characterisation of suprathermal electron pitch-angle distributions”, Astronomy & Astrophysics, vol. 635, art. no. A79, pp. 1-13.
Keywords
Sun: heliosphere
Sun: coronal mass ejections (CMEs)
Solar wind
Methods: data analysis
Methods: statistical
Methods: analytical
Project
info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2013-2016/ESP2017-88436-R/ES/ENERGETIC PARTICLE DETECTOR EN SOLAR ORBITER: FASES D Y E/
Document type
info:eu-repo/semantics/article
Version
info:eu-repo/semantics/acceptedVersion
Publisher's version
https://doi.org/10.1051/0004-6361/201936601Rights
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
© ESO 2020
Access rights
info:eu-repo/semantics/openAccess
Abstract
Context. Suprathermal electron pitch-angle distributions (PADs) contain substantial information about the magnetic topology of the solar wind. Their characterisation and quantification allow us to automatically identify periods showing certain characteristics. Aims. This work presents a robust automatic method for the identification and statistical study of two different types of PADs: bidirectional suprathermal electrons (BDE, often associated with closed magnetic structures) and isotropic (likely corresponding to solar-detached magnetic field lines or highly scattered electrons). Methods. Spherical harmonics were fitted to the observed suprathermal PADs of the 119&-193 eV energy channel of STEREO/SWEA from March 2007 to July 2014, and they were characterised using signal processing analysis in order to identify periods of isotropic and bidirectional PADs. The characterisation has been validated by comparing the results obtained here with those of previous studies. Results. Interplanetary coronal mass ejections (ICMEs) present longer BDE periods inside the magnetic obstacles. A significant amount of BDE remain after the end of the ICME. Isotropic PADs are found in the sheath of the ICMEs, and at the post-ICME region likely due to the erosion of the magnetic field lines. Both isotropy and BDE are solar-cycle dependent. The isotropy observed by STEREO shows a nearly annual periodicity, which requires further investigation. There is also a correspondence between the number of ICMEs observed and the percentage of time showing BDE. Conclusions. A method to characterise PADs has been presented and applied to the automatic identification of two relevant distributions that are commonly observed in the solar wind, such as BDE and isotropy. Four catalogues (STEREO-A and STEREO-B for isotropic and BDE periods of at least 10 min) based on this identification are provided for future applications.
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