In situ multi-spacecraft and remote imaging observations of the first CME detected by Solar Orbiter and BepiColombo

Abstract

Context. On 2020 April 19 a coronal mass ejection (CME) was detected in situ by Solar Orbiter at a heliocentric distance of about 0.8 AU. The CME was later observed in situ on April 20 by the Wind and BepiColombo spacecraft whilst BepiColombo was located very close to Earth. This CME presents a good opportunity for a triple radial alignment study, as the spacecraft were separated by less than 5° in longitude. The source of the CME, which was launched on April 15, was an almost entirely isolated streamer blowout. The Solar Terrestrial Relations Observatory (STEREO)-A spacecraft observed the event remotely from −75.1° longitude, which is an exceptionally well suited viewpoint for heliospheric imaging of an Earth directed CME. Aims. The configuration of the four spacecraft has provided an exceptionally clean link between remote imaging and in situ observations of the CME. We have used the in situ observations of the CME at Solar Orbiter, Wind, and BepiColombo and the remote observations of the CME at STEREO-A to determine the global shape of the CME and its evolution as it propagated through the inner heliosphere. Methods. We used three magnetic flux rope models that are based on different assumptions about the flux rope morphology to interpret the large-scale structure of the interplanetary CME (ICME). The 3DCORE model assumes an elliptical cross-section with a fixed aspect-ratio calculated by using the STEREO Heliospheric Imager (HI) observations as a constraint. The other two models are variants of the kinematically-distorted flux rope (KFR) technique, where two flux rope cross-sections are considered: one in a uniform solar wind and another in a solar-minimum-like structured solar wind. Analysis of CME evolution has been complemented by the use of (1) the ELEvoHI model to compare predicted CME arrival times and confirm the connection between the imaging and in situ observations, and (2) the PREDSTORM model, which provides an estimate of the Dst index at Earth using Solar Orbiter magnetometer data as if it were a real–time upstream solar wind monitor. Results. A clear flattening of the CME cross-section has been observed by STEREO-A, and further confirmed by comparing profiles of the flux rope models to the in situ data, where the distorted flux rope cross-section qualitatively agrees most with in situ observations of the magnetic field at Solar Orbiter. Comparing in situ observations of the magnetic field between spacecraft, we find that the dependence of the maximum (mean) magnetic field strength decreases with heliocentric distance as r−1.24 ± 0.50 (r−1.12 ± 0.14), which is in disagreement with previous studies. Further assessment of the axial and poloidal magnetic field strength dependencies suggests that the expansion of the CME is likely neither self-similar nor cylindrically symmetric.

Solar origins of a strong stealth CME detected by Solar Orbiter

“…The shock was then observed The in situ data reveal a clear magnetic flux rope structure, constrained by the vertical dashed lines in Fig. 1, where the leading edge times of the magnetic flux rope are 08:59 UT on 19 April 2020 at Solar Orbiter and 07:56 UT on 20 April 2020 at Wind (defined by Davies et al 2021). The CME can be classified as a magnetic cloud, meeting criteria detailed by Burlaga et al (1981a).…”

“…The high speed stream may also be the reason we observe a stronger magnetic field strength than expected within the CME, where the mean magnetic field strength of the flux rope (18.4 nT at Solar Orbiter and 13.6 nT at Wind) is much We have applied a semi-empirical 3D flux rope model to the Solar Orbiter data (3DCORE, Möstl et al 2018;Weiss et al 2021) in order to derive global parameters of the flux rope within this ICME. Detailed results are given in Davies et al (2021) and Freiherr von Forstner et al (2021), and work on a paper on simultaneous multi-point fitting of the Solar Orbiter, Wind, and BepiColombo flux rope magnetic field data is underway (Weiss et al 2021b, in prep.). Here we present additional information on the magnetic flux derived from the 3DCORE fit on the Solar Orbiter MAG data only.…”

“…Qiu et al 2007;Möstl et al 2009), and this yields parameters of a flux rope that was pre-existing in the solar corona. Davies et al (2021) report the fit results with the 3DCORE technique applied to the Solar Orbiter data, propagated to 1 AU: an axial field strength of B 0 = 14.3 ± 0.9 nT, a flux rope diameter of D 1AU = 0.114 ± 0.022 AU, and a twist of τ = −3.7 ± 0.6 field line turns over the full torus (τ < 0 implies left-handed chirality), or τ 1AU = −0.6 ± 0.1 turns per AU. We have numerically integrated the flux rope cross section to find an axial flux of Φ ax = 0.30 ± 0.06 × 10 21 Mx.…”

“…The encounter took place on 19 April 2020 at a heliocentric distance of 0.809 AU. The details of the CME's structure and propagation in the inner heliosphere are reported in Davies et al (2021) and information on the corresponding Forbush decrease can be found in Freiherr von Forstner et al (2021). The interplanetary CME had a clear flux rope structure and its arrival at Earth produced a Dst minimum of -60 nT on 20 April 2020 and a category G1 geomagnetic storm.…”

Configuration of a Magnetic Cloud From Solar Orbiter and Wind Spacecraft In-situ Measurements

“…In this research topic collection, Song et al [15] reexamined this event from the perspective of implications for elemental charge states in MCs. Lately, Davies et al [16] analyzed an MC event detected in-situ by the Solar Orbiter (SO), Wind, and Bepi Colombo spacecraft in April 2020, and related to its solar source CME eruption by using the coronagraphic imaging observations from STEREO. We will re-examine this MC event by using the in-situ measurements from both SO and Wind spacecraft.…”