Uncovering erosion effects on magnetic flux rope twist

Uncovering erosion effects on magnetic flux rope twist Sanchita Pal, Emilia Kilpua, Simon Good, Jens Pomoell, Daniel Price University of Helsinki, Finland

Flux rope (FR) CME & its interplanetary counterpart – Magnetic cloud Credit: STEREO& LASCO & SDO Credit: Demoulin 2020

Importance of Twist -- CME’s intrinsic property CME and its. II. interplanetary counterpart – Magnetic cloud I. Schematic of FR in the interplanetary medium. Zurbuchen and Richardson, 2006 • Geo-effectiveness of CME flux ropes FR formation. Credit: NASA Due to Magnetic reconnection? ? • How does a flux rope form during CME eruption Is it pre-existing? ?

MC interaction with ambient solar wind CME and its interplanetary counterpart – Magnetic cloud Draping of IMF around MC (Pal et al. 2020) • MC may magnetically reconnect with ambient solar wind magnetic field (Dasso et al. 2006, Ruffenach et al. 2012) • Flux rope erodes due to reconnection (Ruffenach et al. 2015, Pal et al. 2020)

How to measure a flux rope’s erosion? -- by comparing flux rope’s magnetic flux in azimuthal plane in Sun-Earth domain FR’s near-Earth azimuthal flux FR’s near-Sun azimuthal flux determination: FR azimuthal flux measurement using solar remote sensing observations MC azimuthal flux measurement from in situ data

How to determine the twist profile of flux rope? S/C path p MC axis Cylindrical MC structure Linear least-square fit of MC

Events and their analysis Event MC start MC end CME obs Eruptive ev Solar Loc 1 5 th April 2010 11: 57 6 th April 2010 13: 10 3 rd April 2010 10: 33 Flare B-class S 25 E 00 2 13 th July 2013 4: 39 14 th July 2013 20: 40 9 th July 2013 15: 12 Filament N 19 E 14 Event 1 Event flux analysis and comparison Event 1 Event 2

Effect of erosion on the twist profile of events Event 1 p=0. 03 Percentage of erosion ~ 35% Event 2 p=0. 03 p=0. 19 Percentage of erosion ~ 8% Generic twist profile (Lanbere et al. 2020) Twist profile in FR cross-section of Event 1 and 2 § Twist increases towards the centre at inner core, remain almost constant at the outer core and moderately increases towards the outer shell § Erosion can peel off twisted outer core or envelop of flux ropes

Conclusions § Due to the presence of ‘seed FR’ twist increases towards the centre at inner core. § Coronal magnetic reconnection forms twisted envelop of eruptive flux ropes. § Erosion can remove twisted field lines from the outer shell of FRs. Inner core twist Outer core twist Schematic of twisted FRs Outer shell/envelop twist